Early morning (my time) there was an intermediate depth earthquake in the Banda Sea.
https://earthquake.usgs.gov/earthquakes/eventpage/us70009b14/executive
This earthquake was a strike-slip earthquake in the Australia plate. There are analogical earthquakes in the same area in 1963, 1987, 2005, and 2012 that appear to have occurred on the same fault.
In June 2019 there was an earthquake nearby with a similar mechanism.
Below is my interpretive poster for this earthquake
- I plot the seismicity from the past 3 months, with diameter representing magnitude (see legend). I include earthquake epicenters from 1920-2020 with magnitudes M ≥ 6.5.
- I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
- A review of the basic base map variations and data that I use for the interpretive posters can be found on the Earthquake Reports page.
- Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.
- In a map below, I include a transparent overlay of the Global Strain Rate Map (Kreemer et al., 2014).
- The mission of the Global Strain Rate Map (GSRM) project is to determine a globally self-consistent strain rate and velocity field model, consistent with geodetic and geologic field observations. The overall mission also includes:
- contributions of global, regional, and local models by individual researchers
- archive existing data sets of geologic, geodetic, and seismic information that can contribute toward a greater understanding of strain phenomena
- archive existing methods for modeling strain rates and strain transients
- The completed global strain rate map will provide a large amount of information that is vital for our understanding of continental dynamics and for the quantification of seismic hazards.
- The version used in the poster(s) below is an update to the original 2004 map (Kreemer et al., 2000, 2003; Holt et al., 2005).
Global Strain
- In the upper right corner is a map showing historic seismicity, fault lines, and the global strain rate map (red shows area of higher tectonic strain).
- In the lower right corner is a low angle oblique view of the tectonic plate configuration (Pownall et al., 2014).
- In the upper left corner are maps that show the seismic hazard and seismic risk for Indonesia. I spend more time explaining this below.
- In the center top-left is a map that shows earthquake intensity using the Modified Mercalli Intensity (MMI) Scale.
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
- Here is the map with a month’s seismicity plotted.
- Here is the poster from the nearby earthquake in June of 2019.
Other Report Pages
Some Relevant Discussion and Figures
- Here is a tectonic map for this part of the world from Zahirovic et al., 2014. They show a fracture zone where the M 7.3 earthquake happened. I left out all the acronym definitions (you’re welcome), but they are listed in the paper.
Regional tectonic setting with plate boundaries (MORs/transforms = black, subduction zones = teethed red) from Bird (2003) and ophiolite belts representing sutures modified from Hutchison (1975) and Baldwin et al. (2012). West Sulawesi basalts are from Polvé et al. (1997), fracture zones are from Matthews et al. (2011) and basin outlines are from Hearn et al. (2003).
- This is a great visualization showing the Australia plate and how it formed the largest forearc basin on Earth (Pownall et al., 2014).
- The maps on the left show a time history of the tectonics. The low angle oblique view on the right shows the dipping crust (north is not always up, as in this figure).
- In the lower right, they show how there is strike-slip faulting along the Seram trough also (I left out the figure caption for E).
Reconstructions of eastern Indonesia, adapted from Hall (2012), depict collision of Australia with Southeast Asia and slab rollback into Banda Embayment. Yellow star indicates Seram. Oceanic crust is shown in purple (older than 120 Ma) and blue (younger than 120 Ma); submarine arcs and oceanic plateaus are shown in cyan; volcanic island arcs, ophiolites, and material accreted along plate margins are shown in green. A: Reconstruction at 15 Ma. B: Reconstruction at 7 Ma. C: Reconstruction at 2 Ma. D: Visualization of present-day slab morphology of proto–Banda Sea based on earthquake hypocenter distribution and tomographic models
- Here is a map and some cross sections showing seismic tomography (like C-T scans into the Earth using seismic waves instead of X-Rays). The map shows the location of the cross sections (Spakman et al., 2010).
The Banda arc and surrounding region. 200 m and 4,000 m bathymetric contours are indicated. The numbered black lines are Benioff zone contours in kilometres. The red triangles are Holocene volcanoes (http://www.volcano.si.edu/world/). Ar=Aru, Ar Tr=Aru trough, Ba=Banggai Islands, Bu=Buru, SBS=South Banda Sea, Se=Seram, Sm=Sumba, Su=Sula Islands, Ta=Tanimbar, Ta Tr=Tanimbar trough, Ti=Timor, W=Weber Deep.
Tomographic images of the Banda slab. Vertical sections through the tomography model along the lines shown in Fig. 1. Colours: P-wave anomalies with reference to velocity model ak135 (ref. 30). Dots: earthquake hypocentres within 12 km of the section. The dashed lines are phase changes at ~410 km and ~660 km. The sections are plotted without vertical exaggeration; the horizontal axis is in degrees. The labelled positive anomalies are the Sunda (Su) and Banda (Ba) slabs: BuDdetached slab under Buru, FlDslab under Flores, SDslab under Seram, TDslab under Timor. a, The Sunda slab enters the lower mantle whereas the Banda embayment slab is entirely in the upper mantle with the change under Sulawesi. b–e, Banda slab morphology in sections parallel to Australia plate motion shows a transition from a steep slab with a flat section (fs) (b) to a spoon shape shallowing eastward (c–e).
- Here is the map from Benz et al. (2011).
- Here is the tectonic map from Hengesh and Whitney (2016)
Illustration of major tectonic elements in triple junction geometry: tectonic features labeled per Figure 1; seismicity from ISC-GEM catalog [Storchak et al., 2013]; faults in Savu basin from Rigg and Hall [2011] and Harris et al. [2009]. Purple line is edge of Australian continental basement and fore arc [Rigg and Hall, 2011]. Abbreviations: AR = Ashmore Reef; SR = Scott Reef; RS = Rowley Shoals; TCZ = Timor Collision Zone; ST = Savu thrust; SB = Savu Basin; TT = Timor thrust; WT =Wetar thrust; WASZ = Western Australia Shear Zone. Open arrows indicate relative direction of motion; solid arrows direction of vergence.
- Here is the Audley (2011) cross section showing how the backthrust relates to the subduction zone beneath Timor. I include their figure caption in blockquote below.
Cartoon cross section of Timor today, (cf. Richardson & Blundell 1996, their BIRPS figs 3b, 4b & 7; and their fig. 6 gravity model 2 after Woodside et al. 1989; and Snyder et al. 1996 their fig. 6a). Dimensions of the filled 40 km deep present-day Timor Tectonic Collision Zone are based on BIRPS seismic, earthquake seismicity and gravity data all re-interpreted here from Richardson & Blundell (1996) and from Snyder et al. (1996). NB. The Bobonaro Melange, its broken formation and other facies are not indicated, but they are included with the Gondwana mega-sequence. Note defunct Banda Trench, now the Timor TCZ, filled with Australian continental crust and Asian nappes that occupy all space between Wetar Suture and the 2–3 km deep deformation front north of the axis of the Timor Trough. Note the much younger decollement D5 used exactly the same part of the Jurassic lithology of the Gondwana mega-sequence in the older D1 decollement that produced what appears to be much stronger deformation.
- Here is a figure showing the regional geodetic motions (Bock et al., 2003). I include their figure caption below as a blockquote.
Topographic and tectonic map of the Indonesian archipelago and surrounding region. Labeled, shaded arrows show motion (NUVEL-1A model) of the first-named tectonic plate relative to the second. Solid arrows are velocity vectors derived from GPS surveys from 1991 through 2001, in ITRF2000. For clarity, only a few of the vectors for Sumatra are included. The detailed velocity field for Sumatra is shown in Figure 5. Velocity vector ellipses indicate 2-D 95% confidence levels based on the formal (white noise only) uncertainty estimates. NGT, New Guinea Trench; NST, North Sulawesi Trench; SF, Sumatran Fault; TAF, Tarera-Aiduna Fault. Bathymetry [Smith and Sandwell, 1997] in this and all subsequent figures contoured at 2 km intervals.
- Whitney and Hengesh (2015) used GPS modeling to suggest a model of plate blocks. Below are their model results.
Plate boundary segments in the Banda Arc region from Nugroho et al (2009). Numbers inside rectangles show possible micro-plate blocks near the Sumba Triple Junction (colored) based on GPS velocities (black arrows) with in a stable Eurasian reference frame.
- Here is the conceptual model from Whitney and Hengesh (2015) that shows how left-lateral strike-slip faulting can come into the region.
Schematic map views of kinematic relations between major crustal elements in the Sumba Triple Junction region. CTZ= collisional tectonic zone. Red arrow size designates schematic plate motion relations based on geological data relative to a fixed Sunda shelf reference frame (pin).
Seismic Hazard and Seismic Risk
- These are the two maps shown in the map above, the GEM Seismic Hazard and the GEM Seismic Risk maps from Pagani et al. (2018) and Silva et al. (2018).
- The GEM Seismic Hazard Map:
- The Global Earthquake Model (GEM) Global Seismic Hazard Map (version 2018.1) depicts the geographic distribution of the Peak Ground Acceleration (PGA) with a 10% probability of being exceeded in 50 years, computed for reference rock conditions (shear wave velocity, VS30, of 760-800 m/s). The map was created by collating maps computed using national and regional probabilistic seismic hazard models developed by various institutions and projects, and by GEM Foundation scientists. The OpenQuake engine, an open-source seismic hazard and risk calculation software developed principally by the GEM Foundation, was used to calculate the hazard values. A smoothing methodology was applied to homogenise hazard values along the model borders. The map is based on a database of hazard models described using the OpenQuake engine data format (NRML). Due to possible model limitations, regions portrayed with low hazard may still experience potentially damaging earthquakes.
- Here is a view of the GEM seismic hazard map for Indonesia.
- The GEM Seismic Risk Map:
- The Global Seismic Risk Map (v2018.1) presents the geographic distribution of average annual loss (USD) normalised by the average construction costs of the respective country (USD/m2) due to ground shaking in the residential, commercial and industrial building stock, considering contents, structural and non-structural components. The normalised metric allows a direct comparison of the risk between countries with widely different construction costs. It does not consider the effects of tsunamis, liquefaction, landslides, and fires following earthquakes. The loss estimates are from direct physical damage to buildings due to shaking, and thus damage to infrastructure or indirect losses due to business interruption are not included. The average annual losses are presented on a hexagonal grid, with a spacing of 0.30 x 0.34 decimal degrees (approximately 1,000 km2 at the equator). The average annual losses were computed using the event-based calculator of the OpenQuake engine, an open-source software for seismic hazard and risk analysis developed by the GEM Foundation. The seismic hazard, exposure and vulnerability models employed in these calculations were provided by national institutions, or developed within the scope of regional programs or bilateral collaborations.
- Here is a view of the GEM seismic risk map for Indonesia.
- M 9.2 Andaman-Sumatra subduction zone 2014 Earthquake Anniversary
- M 9.2 Andaman-Sumatra subduction zone SASZ Fault Deformation
- M 9.2 Andaman-Sumatra subduction zone 2016 Earthquake Anniversary
- 2020.05.06 M 6.8 Banda Sea
- 2019.08.02 M 6.9 Indonesia
- 2019.06.23 M 7.3 Banda Sea
- 2019.04.12 M 6.8 Sulawesi, Indonesia
- 2018.09.28 M 7.5 Sulawesi
- 2018.10.16 M 7.5 Sulawesi UPDATE #1
- 2018.08.19 M 6.9 Lombok, Indonesia
- 2018.08.05 M 6.9 Lombok, Indonesia
- 2018.07.28 M 6.4 Lombok, Indonesia
- 2017.12.15 M 6.5 Java
- 2017.08.31 M 6.3 Mentawai, Sumatra
- 2017.08.13 M 6.4 Bengkulu, Sumatra, Indonesia
- 2017.05.29 M 6.8 Sulawesi, Indonesia
- 2017.03.14 M 6.0 Sumatra
- 2017.03.01 M 5.5 Banda Sea
- 2016.10.19 M 6.6 Java
- 2016.03.02 M 7.8 Sumatra/Indian Ocean
- 2015.07.22 M 5.8 Andaman Sea
- 2015.11.08 M 6.4 Nicobar Isles
- 2012.04.11 M 8.6 Sumatra outer rise
- 2004.12.26 M 9.2 Andaman-Sumatra subduction zone
Indonesia | Sumatra
General Overview
Earthquake Reports
Social Media
- Frisch, W., Meschede, M., Blakey, R., 2011. Plate Tectonics, Springer-Verlag, London, 213 pp.
- Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
- Holt, W. E., C. Kreemer, A. J. Haines, L. Estey, C. Meertens, G. Blewitt, and D. Lavallee (2005), Project helps constrain continental dynamics and seismic hazards, Eos Trans. AGU, 86(41), 383–387, , https://doi.org/10.1029/2005EO410002. /li>
- Jessee, M.A.N., Hamburger, M. W., Allstadt, K., Wald, D. J., Robeson, S. M., Tanyas, H., et al. (2018). A global empirical model for near-real-time assessment of seismically induced landslides. Journal of Geophysical Research: Earth Surface, 123, 1835–1859. https://doi.org/10.1029/2017JF004494
- Kreemer, C., J. Haines, W. Holt, G. Blewitt, and D. Lavallee (2000), On the determination of a global strain rate model, Geophys. J. Int., 52(10), 765–770.
- Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8–34, , https://doi.org/10.1046/j.1365-246X.2003.01917.x.
- Kreemer, C., G. Blewitt, E.C. Klein, 2014. A geodetic plate motion and Global Strain Rate Model in Geochemistry, Geophysics, Geosystems, v. 15, p. 3849-3889, https://doi.org/10.1002/2014GC005407.
- Meyer, B., Saltus, R., Chulliat, a., 2017. EMAG2: Earth Magnetic Anomaly Grid (2-arc-minute resolution) Version 3. National Centers for Environmental Information, NOAA. Model. https://doi.org/10.7289/V5H70CVX
- Müller, R.D., Sdrolias, M., Gaina, C. and Roest, W.R., 2008, Age spreading rates and spreading asymmetry of the world’s ocean crust in Geochemistry, Geophysics, Geosystems, 9, Q04006, https://doi.org/10.1029/2007GC001743
- Pagani,M. , J. Garcia-Pelaez, R. Gee, K. Johnson, V. Poggi, R. Styron, G. Weatherill, M. Simionato, D. Viganò, L. Danciu, D. Monelli (2018). Global Earthquake Model (GEM) Seismic Hazard Map (version 2018.1 – December 2018), DOI: 10.13117/GEM-GLOBAL-SEISMIC-HAZARD-MAP-2018.1
- Silva, V ., D Amo-Oduro, A Calderon, J Dabbeek, V Despotaki, L Martins, A Rao, M Simionato, D Viganò, C Yepes, A Acevedo, N Horspool, H Crowley, K Jaiswal, M Journeay, M Pittore, 2018. Global Earthquake Model (GEM) Seismic Risk Map (version 2018.1). https://doi.org/10.13117/GEM-GLOBAL-SEISMIC-RISK-MAP-2018.1
- Zhu, J., Baise, L. G., Thompson, E. M., 2017, An Updated Geospatial Liquefaction Model for Global Application, Bulletin of the Seismological Society of America, 107, p 1365-1385, https://doi.org/0.1785/0120160198
- Audley-Charles, M.G., 1986. Rates of Neogene and Quaternary tectonic movements in the Southern Banda Arc based on micropalaeontology in: Journal of fhe Geological Society, London, Vol. 143, 1986, pp. 161-175.
- Audley-Charles, M.G., 2011. Tectonic post-collision processes in Timor, Hall, R., Cottam, M. A. &Wilson, M. E. J. (eds) The SE Asian Gateway: History and Tectonics of the Australia–Asia Collision. Geological Society, London, Special Publications, 355, 241–266.
- Baldwin, S.L., Fitzgerald, P.G., and Webb, L.E., 2012. Tectonics of the New Guinea Region in Annu. Rev. Earth Planet. Sci., v. 41, p. 485-520.
- Benz, H.M., Herman, Matthew, Tarr, A.C., Hayes, G.P., Furlong, K.P., Villaseñor, Antonio, Dart, R.L., and Rhea, Susan, 2011. Seismicity of the Earth 1900–2010 New Guinea and vicinity: U.S. Geological Survey Open-File Report 2010–1083-H, scale 1:8,000,000.
- Given, J. W., and H. Kanamori (1980). The depth extent of the 1977 Sumbawa, Indonesia, earthquake, in EOS Trans. AGU., v. 61, p. 1044.
- Gusnman, A.R., Tanioka, Y., Matsumoto, H., and Iwasakai, S.-I., 2009. Analysis of the Tsunami Generated by the Great 1977 Sumba Earthquake that Occurred in Indonesia in BSSA, v. 99, no. 4, p. 2169-2179, https://doi.org/10.1785/0120080324
- Hall, R., 2011. Australia-SE Asia collision: plate tectonics and crustal flow in Geological Society, London, Special Publications 2011; v. 355; p. 75-109 doi: 10.1144/SP355.5
- Hangesh, J. and Whitney, B., 2014. Quaternary Reactivation of Australia’s Western Passive Margin: Inception of a New Plate Boundary? in: 5th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA), 21-27 September 2014, Busan, Korea, 4 pp.
- Okal, E. A., & Reymond, D., 2003. The mechanism of great Banda Sea earthquake of 1 February 1938: applying the method of preliminary determination of focal mechanism to a historical event in EPSL, v. 216, p. 1-15.
- Osada, M. and Abe, K., 1981. Mechanism and tectonic implications of the great Banda Sea earthquake of November 4, 1963 in Physics of the Earth and Plentary Interiors, v. 25, p. 129-139
- Pownall, J.M., Hall, R., Armstrong,, R.A., and Forster, M.A., 2014. Earth’s youngest known ultrahigh-temperature granulites discovered on Seram, eastern Indonesia in Geology, v. 42, no. 4, p. 379-282, https://doi.org/10.1130/G35230.1
- Spakman, W. and Hall, R., 2010. Surface deformation and slab–mantle interaction during Banda arc subduction rollback in Nature Geosceince, v. 3, p. 562-566, https://doi.org/10.1038/NGEO917
- Whitney, B.B. and Hengesh, J.V., 2015. A new model for active intraplate tectonics in western Australia in Proceedings of the Tenth Pacific Conference on Earthquake Engineering Building an Earthquake-Resilient Pacific 6-8 November 2015, Sydney, Australia, paper number 82
- Zahirovic, S., Seton, M., and Müller, R.D., 2014. The Cretaceous and Cenozoic tectonic evolution of Southeast Asia in Solid Earth, v. 5, p. 227-273, doi:10.5194/se-5-227-2014
References:
Basic & General References
Specific References
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Well, yesterday I was preparing some updates to the Ridgecrest Earthquake following my field work with my colleagues at the California Geological Survey (where I work) and the U.S. Geological Survey. We spent the week documenting surface ruptures associated with the M 6.4 and M 7.1 Ridgecrest Earthquake Sequence. (it is currently named the Searles Valley Earthquake Sequence, but I am calling it the Ridgecrest Earthquake)
Impact of Earthquake Now I can get back to working on a Ridgecrest update… stay tuned. (the maps are already made) I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). There are many different ways in which a landslide can be triggered. The first order relations behind slope failure (landslides) is that the “resisting” forces that are preventing slope failure (e.g. the strength of the bedrock or soil) are overcome by the “driving” forces that are pushing this land downwards (e.g. gravity). The ratio of resisting forces to driving forces is called the Factor of Safety (FOS). We can write this ratio like this: FOS = Resisting Force / Driving Force When FOS > 1, the slope is stable and when FOS < 1, the slope fails and we get a landslide. The illustration below shows these relations. Note how the slope angle α can take part in this ratio (the steeper the slope, the greater impact of the mass of the slope can contribute to driving forces). The real world is more complicated than the simplified illustration below.
Nowicki Jessee and others (2018) is the preferred model for earthquake-triggered landslide hazard. Our primary landslide model is the empirical model of Nowicki Jessee and others (2018). The model was developed by relating 23 inventories of landslides triggered by past earthquakes with different combinations of predictor variables using logistic regression. The output resolution is ~250 m. The model inputs are described below. More details about the model can be found in the original publication. We modify the published model by excluding areas with slopes <5° and changing the coefficient for the lithology layer "unconsolidated sediments" from -3.22 to -1.36, the coefficient for "mixed sedimentary rocks" to better reflect that this unit is expected to be weak (more negative coefficient indicates stronger rock).To exclude areas of insignificantly small probabilities in the computation of aggregate statistics for this model, we use a probability threshold of 0.002.
Here is an excellent educational video from IRIS and a variety of organizations. The video helps us learn about how earthquake intensity gets smaller with distance from an earthquake. The concept of liquefaction is reviewed and we learn how different types of bedrock and underlying earth materials can affect the severity of ground shaking in a given location. The intensity map above is based on a model that relates intensity with distance to the earthquake, but does not incorporate changes in material properties as the video below mentions is an important factor that can increase intensity in places.
Zhu and others (2017) is the preferred model for liquefaction hazard. The model was developed by relating 27 inventories of liquefaction triggered by past earthquakes to globally-available geospatial proxies (summarized below) using logistic regression. We have implemented the global version of the model and have added additional modifications proposed by Baise and Rashidian (2017), including a peak ground acceleration (PGA) threshold of 0.1 g and linear interpolation of the input layers. We also exclude areas with slopes >5°. We linearly interpolate the original input layers of ~1 km resolution to 500 m resolution. The model inputs are described below. More details about the model can be found in the original publication.
Here is a map that shows a comparison of modeled shaking intensity for both the M 6.9 Molucca Strait (the left panel) and M 7.3 Halmahera (the right panel) earthquakes. The legend shows the MMI scale, which I discuss above.
Annual probability of experiencing a tsunami with a height at the coast of (a) 0.5m (a tsunami warning) and (b) 3m (a major tsunami warning).
Regional tectonic setting with plate boundaries (MORs/transforms = black, subduction zones = teethed red) from Bird (2003) and ophiolite belts representing sutures modified from Hutchison (1975) and Baldwin et al. (2012). West Sulawesi basalts are from Polvé et al. (1997), fracture zones are from Matthews et al. (2011) and basin outlines are from Hearn et al. (2003).
Along its western margin, the Philippine Sea plate is associated with a zone of oblique convergence with the Sunda plate. This highly active convergent plate boundary extends along both sides the Philippine Islands, from Luzon in the north to Sulawesi in the south. The tectonic setting of the Philippines is unusual in several respects: it is characterized by opposite-facing subduction systems on its east and west sides; the archipelago is cut by a major transform fault, the Philippine Fault; and the arc complex itself is marked by volcanism, faulting, and high seismic activity. Subduction of the Philippine Sea plate occurs at the eastern margin of the archipelago along the Philippine Trench and its northern extension, the East Luzon Trough. The East Luzon Trough is thought to be an unusual example of a subduction zone in the process of formation, as the Philippine Trench system gradually extends northward (Hamburger and others, 1983).
Topographic and tectonic map of the Indonesian archipelago and surrounding region. Labeled, shaded arrows show motion (NUVEL-1A model) of the first-named tectonic plate relative to the second. Solid arrows are velocity vectors derived from GPS surveys from 1991 through 2001, in ITRF2000. For clarity, only a few of the vectors for Sumatra are included. The detailed velocity field for Sumatra is shown in Figure 5. Velocity vector ellipses indicate 2-D 95% confidence levels based on the formal (white noise only) uncertainty estimates. NGT, ew Guinea Trench; NST, North Sulawesi Trench; SF, Sumatran Fault; TAF, Tarera-Aiduna Fault. Bathymetry [Smith and Sandwell, 1997] in this and all subsequent figures contoured at 2 km intervals
3D cartoon of plate boundaries in the Molucca Sea region modified from Hall et al. (1995). Although seismicity identifies a number of plates there are no continuous boundaries, and the Cotobato, North Sulawesi and Philippine Trenches are all intraplate features. The apparent distinction between different crust types, such as Australian continental crust and oceanic crust of the Philippine and Molucca Sea, is partly a boundary inactive since the Early Miocene (east Sulawesi) and partly a younger but now probably inactive boundary of the Sorong Fault. The upper crust of this entire region is deforming in a much more continuous way than suggested by this cartoon.
(A) Location and major tectonic features of the Molucca Sea region. Small, black-fi lled triangles are modern volcanoes. Bathymetric contours are at 200, 2000, 4000, and 6000 m. Large barbed lines are subduction zones, and small barbed lines are thrusts. (B) Cross section across the Halmahera and Sangihe Arcs on section line B. Thrusts on each side of the Molucca Sea are directed outward toward the adjacent arcs, although the subducting Molucca Sea plate dips east beneath Halmahera and west below the Sangihe Arc. (C) Inset is the restored cross section of the Miocene–Pliocene Weda Bay Basin of SW Halmahera on section line C, fl attened to the Pliocene unconformity, showing estimated thickness of the section
Map of the Molucca Sea, eastern Indonesia, showing I~tions of seismic refraction lines (solid straight lines) and gravity traverses (duhed-dotted lines). Thrust faults are shown with teeth on hanging wall. Triangles represent active volcanoes defining the Sangihe and Halmahera magmatic arcs. Isobath interval is 1 km from Mammericks et al. [1976].
Gravity model for the central Molucca Sea. (II) Crustal model with layers designated by their density contrasts and refraction control points by open circles and vertical bars. (b) Mantle structure used in modeling the gravity profiles in the central Molucca Sea. Figure 124 fits into the small box at the apex of the inverted-V-ehaped lithosphere. Slab dimensions are controlled by earthquake foci (dots) from Hlltherton 11M Dickinaon [1969J, and mantle densities are taken from Grow 11M Rowin [1975J. The column at the left shows assumed densities for the range of depths between the tick marks. The small v pattern represents oceanic crust, and island arc crust is designated by a short parallel line pattern. East is to the right of the figure.
Location map and active faults of the Molucca Sea region. Fault colours: blue, convergence; red, transvergence; yellow, divergence; grey, uncertain motion. Fault abbreviations: CF, Catabato Fault; GF, Gorontalo Fault; NST, North Sulawesi Trench; PKF, Palu-Koro Fault; SF, Sorong Fault.
Sketch geological map of Halmahera based on Apandi & Sudana (1980), Silitonga et al. (1981), Supriatna (1980) & Yasin (1980) and modified after our own observations. Note in particular the absence of thrusting in the NE arm and the major NE-SW fault (the Subaim Fault) running parallel to the south side of Kau Bay.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Today, on #SeismogramSaturday: what are all those strangely-named seismic phases described in seismograms from distant earthquakes? And what do they tell us about Earth’s interior? pic.twitter.com/VJ9pXJFdCy — Jackie Caplan-Auerbach (@geophysichick) February 23, 2019
Updated #aftershocks of the yesterday Mw 7.3 Halmahera #earthquake, seems the EQ has low aftershocks productivity. The Mc is quite large (~3.5) in this region due to the lack of local (distance <100 km) seismic station, but the regional coverage is good. #seismology #gempa pic.twitter.com/wEzwn9fJvR — Dimas Sianipar (@SianiparDimas) July 15, 2019 Mw=7.4, HALMAHERA, INDONESIA (Depth: 17 km), 2019/07/14 09:10:50 UTC – Full details here: https://t.co/dNG7xZttM4 pic.twitter.com/BrD8FJ8ofn — Earthquakes (@geoscope_ipgp) July 14, 2019 Explore the complex region where the M7.3 #Indonesia #earthquake occurred using the IRIS Interactive Earthquake Browser. The size of the dot indicates the magnitude & the color indicates the depth. You can even look at eq hypocenter locations in 3D! https://t.co/Gs3ykBEp0y pic.twitter.com/wEK4g6srok — IRIS Earthquake Sci (@IRIS_EPO) July 14, 2019 potential #tsunami after #Halmahera #earthquake. Tsunami impact highly depends on a still very uncertain rupture mechanism. Recorded wave amplitude of 10 cm near #Gebe. — CATnews | Andreas M. Schäfer (@CATnewsDE) July 14, 2019 potentially expected #aftershocks for today's #Halmahera #earthquake, #Indonesia @ShakingEarth pic.twitter.com/R9RUghePs2 — CATnews | Andreas M. Schäfer (@CATnewsDE) July 14, 2019 BMKG: Halmahera Selatan Masuk Wilayah Seismik Aktif dan Kompleks https://t.co/8XcNfJMQEy — Indonesiainside.id (@indoinsidenews) July 15, 2019
I had been making an update to an earthquake report on a regionally experienced M 5.6 earthquake from coastal northern California when I noticed that there was a M 7.3 earthquake in eastern Indonesia. I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1919-2019 with magnitudes M ≥ 7.0 in one version.
Regional tectonic setting with plate boundaries (MORs/transforms = black, subduction zones = teethed red) from Bird (2003) and ophiolite belts representing sutures modified from Hutchison (1975) and Baldwin et al. (2012). West Sulawesi basalts are from Polvé et al. (1997), fracture zones are from Matthews et al. (2011) and basin outlines are from Hearn et al. (2003).
Reconstructions of eastern Indonesia, adapted from Hall (2012), depict collision of Australia with Southeast Asia and slab rollback into Banda Embayment. Yellow star indicates Seram. Oceanic crust is shown in purple (older than 120 Ma) and blue (younger than 120 Ma); submarine arcs and oceanic plateaus are shown in cyan; volcanic island arcs, ophiolites, and material accreted along plate margins are shown in green. A: Reconstruction at 15 Ma. B: Reconstruction at 7 Ma. C: Reconstruction at 2 Ma. D: Visualization of present-day slab morphology of proto–Banda Sea based on earthquake hypocenter distribution and tomographic models
The Banda arc and surrounding region. 200 m and 4,000 m bathymetric contours are indicated. The numbered black lines are Benioff zone contours in kilometres. The red triangles are Holocene volcanoes (http://www.volcano.si.edu/world/). Ar=Aru, Ar Tr=Aru trough, Ba=Banggai Islands, Bu=Buru, SBS=South Banda Sea, Se=Seram, Sm=Sumba, Su=Sula Islands, Ta=Tanimbar, Ta Tr=Tanimbar trough, Ti=Timor, W=Weber Deep.
Tomographic images of the Banda slab. Vertical sections through the tomography model along the lines shown in Fig. 1. Colours: P-wave anomalies with reference to velocity model ak135 (ref. 30). Dots: earthquake hypocentres within 12 km of the section. The dashed lines are phase changes at ~410 km and ~660 km. The sections are plotted without vertical exaggeration; the horizontal axis is in degrees. The labelled positive anomalies are the Sunda (Su) and Banda (Ba) slabs: BuDdetached slab under Buru, FlDslab under Flores, SDslab under Seram, TDslab under Timor. a, The Sunda slab enters the lower mantle whereas the Banda embayment slab is entirely in the upper mantle with the change under Sulawesi. b–e, Banda slab morphology in sections parallel to Australia plate motion shows a transition from a steep slab with a flat section (fs) (b) to a spoon shape shallowing eastward (c–e).
Illustration of major tectonic elements in triple junction geometry: tectonic features labeled per Figure 1; seismicity from ISC-GEM catalog [Storchak et al., 2013]; faults in Savu basin from Rigg and Hall [2011] and Harris et al. [2009]. Purple line is edge of Australian continental basement and fore arc [Rigg and Hall, 2011]. Abbreviations: AR = Ashmore Reef; SR = Scott Reef; RS = Rowley Shoals; TCZ = Timor Collision Zone; ST = Savu thrust; SB = Savu Basin; TT = Timor thrust; WT =Wetar thrust; WASZ = Western Australia Shear Zone. Open arrows indicate relative direction of motion; solid arrows direction of vergence.
Cartoon cross section of Timor today, (cf. Richardson & Blundell 1996, their BIRPS figs 3b, 4b & 7; and their fig. 6 gravity model 2 after Woodside et al. 1989; and Snyder et al. 1996 their fig. 6a). Dimensions of the filled 40 km deep present-day Timor Tectonic Collision Zone are based on BIRPS seismic, earthquake seismicity and gravity data all re-interpreted here from Richardson & Blundell (1996) and from Snyder et al. (1996). NB. The Bobonaro Melange, its broken formation and other facies are not indicated, but they are included with the Gondwana mega-sequence. Note defunct Banda Trench, now the Timor TCZ, filled with Australian continental crust and Asian nappes that occupy all space between Wetar Suture and the 2–3 km deep deformation front north of the axis of the Timor Trough. Note the much younger decollement D5 used exactly the same part of the Jurassic lithology of the Gondwana mega-sequence in the older D1 decollement that produced what appears to be much stronger deformation.
Topographic and tectonic map of the Indonesian archipelago and surrounding region. Labeled, shaded arrows show motion (NUVEL-1A model) of the first-named tectonic plate relative to the second. Solid arrows are velocity vectors derived from GPS surveys from 1991 through 2001, in ITRF2000. For clarity, only a few of the vectors for Sumatra are included. The detailed velocity field for Sumatra is shown in Figure 5. Velocity vector ellipses indicate 2-D 95% confidence levels based on the formal (white noise only) uncertainty estimates. NGT, New Guinea Trench; NST, North Sulawesi Trench; SF, Sumatran Fault; TAF, Tarera-Aiduna Fault. Bathymetry [Smith and Sandwell, 1997] in this and all subsequent figures contoured at 2 km intervals.
Plate boundary segments in the Banda Arc region from Nugroho et al (2009). Numbers inside rectangles show possible micro-plate blocks near the Sumba Triple Junction (colored) based on GPS velocities (black arrows) with in a stable Eurasian reference frame.
Schematic map views of kinematic relations between major crustal elements in the Sumba Triple Junction region. CTZ= collisional tectonic zone. Red arrow size designates schematic plate motion relations based on geological data relative to a fixed Sunda shelf reference frame (pin).
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Today, on #SeismogramSaturday: what are all those strangely-named seismic phases described in seismograms from distant earthquakes? And what do they tell us about Earth’s interior? pic.twitter.com/VJ9pXJFdCy — Jackie Caplan-Auerbach (@geophysichick) February 23, 2019
Today I awoke to the USGS earthquake notification service email about an earthquake offshore of Sulawesi, Indonesia. There was an earthquake with a magnitude M 6.8 to the southeast of the Donggala/Palu earthquake from 28 September 2018. Here is the comprehensive earthquake report for the Donggala/Palu earthquake, landslides, and tsunami. The M 6.8 temblor is strange because it is oriented in a way that is different from the mapped faults in the region. The mainshock/aftershock sequence suggests a northeast-southwest oriented fault (making this a right-lateral strike slip earthquake). The mapped faults with this orientation are instead left-lateral faults. I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 4.5 and M ≥ 7.5 in different versions.
Regional tectonic setting with plate boundaries (MORs/transforms = black, subduction zones = teethed red) from Bird (2003) and ophiolite belts representing sutures modified from Hutchison (1975) and Baldwin et al. (2012). West Sulawesi basalts are from Polvé et al. (1997), fracture zones are from Matthews et al. (2011) and basin outlines are from Hearn et al. (2003). ANI – Andaman and Nicobar Islands, BD– Billiton Depression, Ba – Bangka Island, BI – Belitung (Billiton) Island, BiS – Bismarck Sea, BP – Benham Plateau, CaR – Caroline Ridge, CS – Celebes Sea, DG– Dangerous Grounds, EauR – Eauripik Ridge, FIN – Finisterre Terrane, GoT – Gulf of Thailand, GR– Gagua Ridge, HAL– Halmahera, HBa – Huatung Basin, KB–Ketungau Basin, KP – Khorat Platform, KT – Kiilsgaard Trough, LS – Luconia Shoals, MacB – Macclesfield Bank, ManTr – Manus Trench, MaTr – Mariana Trench, MB– Melawi Basin, MDB– Minami Daito Basin, MG– Mangkalihat, MIN – Mindoro, MN– Mawgyi Nappe, MoS – Molucca Sea, MS– Makassar Straits, MTr – Mussau Trench, NGTr – New Guinea Trench, NI – Natuna Islands, ODR– Oki Daito Ridge, OJP –Ontong Java Plateau, OSF – Owen Stanley Fault, PAL – Palawan, PhF – Philippine Fault, PT – Paternoster Platform, PTr – Palau Trench, PVB – Parece Vela Basin, RB – Reed Bank, RMF– Ramu-Markham Fault, RRF – Red River fault, SEM– Semitau, ShB – Shikoku Basin, Sol. Sea – Solomon Sea, SPK – Sepik, SPT – abah–Palawan Trough, STr – Sorol Trough, Sul – Sulawesi, SuS – Sulu Sea, TPAA– Torricelli–Prince Alexander Arc, WB–West Burma, WCT–W Caroline Trough, YTr –Yap Trough.
Regional geodynamic sketch that presents the present day deformation model of Sulawesi area (after Beaudouin et al., 2003) and four main deformation systems around the Central Sulawesi block, highlighting the tectonic complexity of Sulawesi. Approximate location of the Central Sulawesi block rotation pole (P) [compatible with both GPS measurements (Walpersdorf et al., 1998a) and earthquake moment tensor analyses (Beaudouin et al., 2003)], as well as the major active structures are reported. Central Sulawesi Fault System (CSFS) is formed by the Palu–Koro and Matano faults. Arrows correspond to the compression and/or extension directions deduced from both inversion and moment tensor analyses of the focal mechanisms; arrow size being proportional to the deformation rate (e.g., Beaudouin et al., 2003).We also represent the focal mechanism provided by the Harvard CMT database [CMT data base, 2005] for the recent large earthquake (Mw=6.2; 2005/1/23; lat.=0.928S; long.=120.108E). The box indicates the approximate location of the Fig. 6 that corresponds to the geological map of the Palu basin region. The bottom inset shows the SE Asia and Sulawesi geodynamic frame where arrows represent the approximate Indo-Australian and Philippines plate motions relative to Eurasia.
Sketch map of the Cenozoic Central Sulawesi fault system. ML represents the Matano Lake, and Leboni RFZ, the Leboni releasing fault zone that connects the Palu–Koro and Matano Faults. Triangles indicate faults with reverse component (triangles on the upthrown block). On this map are reported the fault kinematic measurement sites (geographic coordinates in Table 3).
3D cartoon of plate boundaries in the Molucca Sea region modified from Hall et al. (1995). Although seismicity identifies a number of plates there are no continuous boundaries, and the Cotobato, North Sulawesi and Philippine Trenches are all intraplate features. The apparent distinction between different crust types, such as Australian continental crust and oceanic crust of the Philippine and Molucca Sea, is partly a boundary inactive since the Early Miocene (east Sulawesi) and partly a younger but now probably inactive boundary of the Sorong Fault. The upper crust of this entire region is deforming in a much more continuous way than suggested by this cartoon.
Talaud orogeny in the North Moluccas. Line of section illustrated in Fig. 9 is indicated.
Sulawesi orogeny. Line of section illustrated in Fig. 9 is indicated.
Map of the same area as Figure 1, and drawn largely after the same sources, but modified in the light of the present study. Revised faults are shown in red. Principal differences include the absence of a through-going Sula Thrust, the Sorong Fault as a plate boundary which does not reach the surface, and connection of the Poh Head fault to the region of dextral transpression in the west of the study area. Sources of deformation in the region are indicated by regions of colour.
(a) Shaded relief map of the multibeam data. See inset map for location. Illumination from the NW. (b) Interpreted structural map, showing fault kinematics, basin areas, and fields of debris derived from the collapsing slope in the south. Locations of subsequent figures shown.
Multibeam image showing details of the region of dextral transpression in the west of the study area. See Figure 3b and inset map for location. Antiformal hinge lines marked by black dashed lines, thrusts marked by white dashed lines. Strike-slip faults marked by double half arrows. Maximum horizontal stress orientations for various structures shown in top right.
Tectonic map of the Lesser Sunda Islands, showing the main tectonic units, main faults, bathymetry and location of seismic sections discussed in this paper.
This plot shows the earthquake localizations on a South-North cross section for the lat -14°/-4° long 114°/124° quadrant corresponding to the Lesser Sunda Islands region. The localizations are extracted from the USGS database and corresponds to magnitude greater than 4.5 in the 1973-2004 time period (shallow earthquakes with undetermined depth have been omitted.
Six 15 km deep seismic sections acquired by BGR from west to east traversing oceanic crust, deep sea trench, accretionary prism, outer arc high and fore-arc basin, derived from Kirchoff prestack depth migration (PreSDM) with a frequency range of 4-60 Hz. Profile BGR06-313 shows exemplarily a velocity-depth model according to refraction/wide-angle
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Today, on #SeismogramSaturday: what are all those strangely-named seismic phases described in seismograms from distant earthquakes? And what do they tell us about Earth’s interior? pic.twitter.com/VJ9pXJFdCy — Jackie Caplan-Auerbach (@geophysichick) February 23, 2019
Mw=6.9, SULAWESI, INDONESIA (Depth: 18 km), 2019/04/12 11:40:49 UTC – Full details here: https://t.co/B4ulzvYxd3 pic.twitter.com/udDfN8ktpl — Earthquakes (@geoscope_ipgp) April 12, 2019 Yesterday, a rare Mw 6.8 Luwuk EQ ruptured east of Sulawesi with a strike-slip mech. Try to provide the finite fault model using teleseismic data (ref. Ji et al., 2002). Gray circles are the BMKG's aftershocks. Seems the strike 43 deg. agreed with the aftershocks distribution? pic.twitter.com/ddS9aGf1ev — Dimas Sianipar (@SianiparDimas) April 13, 2019
Here I summarize Earth’s significant seismicity for 2018. I limit this summary to earthquakes with magnitude greater than or equal to M 6.5. I am sure that there is a possibility that your favorite earthquake is not included in this review. Happy New Year. One year of #earthquakes recorded by @INGVterremoti in Italy. About 2500 events with magnitude equal or larger than M2, about seven per day. Data source https://t.co/g1RvR2A989) #Italia #terremoto #Italy #earthquake pic.twitter.com/ft8GAsFjKA — iunio iervolino (@iuniervo) December 31, 2018 Earthquakes of 2018: a quick post summarising global seismic activity last year (i.e., the figures I showed you yesterday). https://t.co/ahdwpf1OFv pic.twitter.com/S438okD8QQ — Chris Rowan (@Allochthonous) January 1, 2019 Global #earthquakes by Magnitude (M5+) by year (2000-18), showing remarkable consistency from geologic forcing. Whereas patterns are understood, they do not permit short-term, local predictions; instead, be informed and be prepared. #geohazards @IRIS_EPO @USGS pic.twitter.com/BmtXhhUvWF — Ben van der Pluijm 🌎 (@vdpluijm) January 2, 2019 The pattern of shallow earthquakes (depth < 33 km) is typical, with much of the country susceptible to regular shallow seismicity, with lower rates in Northland/Auckland and southeast Otago. pic.twitter.com/3jip8Lyje9 — John Ristau 🇨🇦 🇳🇿 (@SinistralSeismo) January 3, 2019
Just a couple hours ago there was an earthquake along the Swan fault, which is the transform plate boundary between the North America and Caribbean plates. The Cayman trough (CT) is a region of oceanic crust, formed at the Mid-Cayman Rise (MCR) oceanic spreading center. To the west of the MCR the CT is bound by the left-lateral strike-slip Swan fault. To the east of the MCR, the CT is bound on the north by the Oriente fault. We had a damaging and (sadly) deadly earthquake in southern Peru in the last 24 hours. This is an earthquake, with magnitude M 7.1, that is associated with the subduction zone forming the Peru-Chile trench (PCT). The Nazca plate (NP) is subducting beneath the South America plate (SAP). There are lots of geologic structures on the Nazca plate that tend to affect how the subduction zone responds during earthquakes (e.g. segmentation). This earthquake appears to be located along a reactivated fracture zone in the GA. There have only been a couple earthquakes in this region in the past century, one an M 6.0 to the east (though this M 6.0 was a thrust earthquake). The Gulf of Alaska shear zone is even further to the east and has a more active historic fault history (a pair of earthquakes in 1987-1988). The magnetic anomalies (formed when the Earth’s magnetic polarity flips) reflect a ~north-south oriented spreading ridge (the anomalies are oriented north-south in the region of today’s earthquake). There is a right-lateral offset of these magnetic anomalies located near the M 7.9 epicenter. Interesting that this right-lateral strike-slip fault (?) is also located at the intersection of the Gulf of Alaska shear zone and the 1988 M 7.8 earthquake (probably just a coincidence?). However, the 1988 M 7.8 earthquake fault plane solution can be interpreted for both fault planes (it is probably on the GA shear zone, but I don’t think that we can really tell). As a reminder, if the M 7.9 earthquake fault is E-W oriented, it would be left-lateral. The offset magnetic anomalies show right-lateral offset across these fracture zones. This was perhaps the main reason why I thought that the main fault was not E-W, but N-S. After a day’s worth of aftershocks, the seismicity may reveal some north-south trends. But, as a drama student in 7th grade (1977), my drama teacher (Ms. Naichbor, rest in peace) asked our class to go stand up on stage. We all stood in a line and she mentioned that this is social behavior, that people tend to stand in lines (and to avoid doing this while on stage). Later, when in college, professors often commented about how people tend to seek linear trends in data (lines). I actually see 3-4 N-S trends and ~2 E-W trends in the seismicity data. There was just now an earthquake in Oaxaca, Mexico between the other large earthquakes from last 2017.09.08 (M 8.1) and 2017.09.08 (M 7.1). There has already been a M 5.8 aftershock.Here is the USGS website for today’s M 7.2 earthquake. This morning (local time in California) there was an earthquake in Papua New Guinea with, unfortunately, a high likelihood of having a good number of casualties. I was working on a project, so could not immediately begin work on this report. We had an M 6.8 earthquake near a transform micro-plate boundary fault system north of New Ireland, Papua New Guinea today. Here is the USGS website for this earthquake. The New Britain region is one of the more active regions in the world. See a list of earthquake reports for this region at the bottom of this page, above the reference list. Well, those earthquakes from earlier, one a foreshock to a later one, were foreshocks to an earthquake today! Here is my report from a couple days ago. The M 6.6 and M 6.3 straddle today’s earthquake and all have similar hypocentral depths. A couple days ago there was a deep focus earthquake in the downgoing Nazca plate deep beneath Bolivia. This earthquake has an hypocentral depth of 562 km (~350 miles). There has been a swarm of earthquakes on the southeastern part of the big island, with USGS volcanologists hypothesizing about magma movement and suggesting that an eruption may be imminent. Here is a great place to find official USGS updates on the volcanism in Hawaii (including maps). This version includes earthquakes M ≥ 3.5 (note the seismicity offshore to the south, this is where the youngest Hawaii volcano is). Below are a series of plots from tide gages installed at several sites in the Hawaii Island Chain. These data are all posted online here and here. Yesterday morning, as I was recovering from working on stage crew for the 34th Reggae on the River (fundraiser for the non profit, the Mateel Community Center), I noticed on social media that there was an M 6.9 earthquake in Lombok, Indonesia. This is sad because of the likelihood for casualties and economic damage in this region. Well, yesterday while I was installing the final window in a reconstruction project, there was an earthquake along the Aleutian Island Arc (a subduction zone) in the region of the Andreanof Islands. Here is the USGS website for the M 6.6 earthquake. This earthquake is close to the depth of the megathrust fault, but maybe not close enough. So, this may be on the subduction zone, but may also be on an upper plate fault (I interpret this due to the compressive earthquake fault mechanism). The earthquake has a hypocentral depth of 20 km and the slab model (see Hayes et al., 2013 below and in the poster) is at 40 km at this location. There is uncertainty in both the slab model and the hypocentral depth. We just had a Great Earthquake in the region of the Fiji Islands, in the central-western Pacific. Great Earthquakes are earthquakes with magnitudes M ≥ 8.0. This ongoing sequence began in late July with a Mw 6.4 earthquake. Followed less than 2 weeks later with a Mw 6.9 earthquake. We just had a M 7.3 earthquake in northern Venezuela. Sadly, this large earthquake has the potential to be quite damaging to people and their belongings (buildings, infrastructure). Well, this earthquake, while having a large magnitude, was quite deep. Because earthquake intensity decreases with distance from the earthquake source, the shaking intensity from this earthquake was so low that nobody submitted a single report to the USGS “Did You Feel It?” website for this earthquake. Following the largest typhoon to strike Japan in a very long time, there was an earthquake on the island of Hokkaido, Japan today. There is lots on social media, including some spectacular views of disastrous and deadly landslides triggered by this earthquake (earthquakes are the number 1 source for triggering of landslides). These landslides may have been precipitated (sorry for the pun) by the saturation of hillslopes from the typhoon. Based upon the USGS PAGER estimate, this earthquake has the potential to cause significant economic damages, but hopefully a small number of casualties. As far as I know, this does not incorporate potential losses from earthquake triggered landslides [yet]. Today, there was a large earthquake associated with the subduction zone that forms the Kermadec Trench. Well, around 3 AM my time (northeastern Pacific, northern CA) there was a sequence of earthquakes including a mainshock with a magnitude M = 7.5. This earthquake happened in a highly populated region of Indonesia. Here is a map that shows the updated USGS model of ground shaking. The USGS prepared an updated earthquake fault slip model that was additionally informed by post-earthquake analysis of ground deformation. The original fault model extended from north of the epicenter to the northernmost extent of Palu City. Soon after the earthquake, Dr. Sotiris Valkaniotis prepared a map that showed large horizontal offsets across the ruptured fault along the entire length of the western margin on Palu Valley. This horizontal offset had an estimated ~8 meters of relative displacement. InSAR analyses confirmed that the coseismic ground deformation extended through Palu Valley and into the mountains to the south of the valley. Synthetic Aperture Radar (SAR) is a remote sensing method that uses Radar to make observations of Earth. These observations include the position of the ground surface, along with other information about the material properties of the Earth’s surface. Landslides during and following the M=7.5 earthquake in central Sulawesi, Indonesia possibly caused the majority of casualties from this catastrophic natural disaster. Volunteers (citizen scientists) have used satellite aerial imagery collected after the earthquake to document the spatial extent and magnitude of damage caused by the earthquake, landslides, and tsunami.
Nowicki Jessee and others (2018) is the preferred model for earthquake-triggered landslide hazard. Our primary landslide model is the empirical model of Nowicki Jessee and others (2018). The model was developed by relating 23 inventories of landslides triggered by past earthquakes with different combinations of predictor variables using logistic regression. The output resolution is ~250 m. The model inputs are described below. More details about the model can be found in the original publication. We modify the published model by excluding areas with slopes <5° and changing the coefficient for the lithology layer "unconsolidated sediments" from -3.22 to -1.36, the coefficient for "mixed sedimentary rocks" to better reflect that this unit is expected to be weak (more negative coefficient indicates stronger rock).To exclude areas of insignificantly small probabilities in the computation of aggregate statistics for this model, we use a probability threshold of 0.002.
Zhu and others (2017) is the preferred model for liquefaction hazard. The model was developed by relating 27 inventories of liquefaction triggered by past earthquakes to globally-available geospatial proxies (summarized below) using logistic regression. We have implemented the global version of the model and have added additional modifications proposed by Baise and Rashidian (2017), including a peak ground acceleration (PGA) threshold of 0.1 g and linear interpolation of the input layers. We also exclude areas with slopes >5°. We linearly interpolate the original input layers of ~1 km resolution to 500 m resolution. The model inputs are described below. More details about the model can be found in the original publication.
In this region of the world, the Solomon Sea plate and the South Bismarck plate converge to form a subduction zone, where the Solomon Sea plate is the oceanic crust diving beneath the S.Bismarck plate. This region of the Pacific-North America plate boundary is at the northern end of the Cascadia subduction zone (CSZ). To the east, the Explorer and Juan de Fuca plates subduct beneath the North America plate to form the megathrust subduction zone fault capable of producing earthquakes in the magnitude M = 9 range. The last CSZ earthquake was in January of 1700, just almost 319 years ago. Before I looked more closely, I thought this sequence might be related to the Kefallonia fault. I prepared some earthquake reports for earthquakes here in the past, in 2015 and in 2016. There was a M = 6.8 earthquake along a transform fault connecting segments of the Mid Atlantic Ridge recently. Today’s earthquake occurred along the convergent plate boundary in southern Alaska. This subduction zone fault is famous for the 1964 March 27 M = 9.2 megathrust earthquake. I describe this earthquake in more detail here. There was a sequence of earthquakes along the subduction zone near New Caledonia and the Loyalty Islands. A large earthquake in the region of the Bering Kresla fracture zone, a strike-slip fault system that coincides with the westernmost portion of the Aleutian trench (which is a subduction zone further to the east). This magnitude M = 7.0 earthquake is related to the subduction zone that forms the Philippine trench (where the Philippine Sea plate subducts beneath the Sunda plate). Here is the USGS website for this earthquake.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
We continue to learn more each day as people collect additional information. Here is my initial Earthquake Report for this M 7.5 Donggala Earthquake. I will attempt to summarize some of what we have learned in the past couple of weeks. I will begin with the earthquake observations, then discuss the tsunami and landslides. The M=7.5 Donggala earthquake struck along the most active and seismically hazardous fault on the island of Sulawesi (Celebes), Indonesia. The Palu-Koro fault has a slip rate of 42 mm per year (Socquet et al., 2006), has a record of M=7-8 prehistoric earthquakes (Watkinson and Hall, 2017), as well as a record of M>7 earthquakes in the 20th century (Gómez et al., 2000). The seismic hazard associated with this fault was well evidenced prior to the earthquake (Cipta et al., 2016). According to the National Disaster Management Authority (Badan Nasional Penanggulangan Bencana, BNPB), there were around 2.4 million people exposed to earthquake intensity MMI V or greater. The Modified Mercalli Intensity (MMI) scale is a measure of how strongly the ground shaking is from an earthquake. MMI V is described as, “Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.” However, the closer one is to the earthquake source, the greater the MMI intensity. There have been reported observations as large as MMI VIII. Perhaps some of the most phenomenal results from remote sensing analyses are coming from the work of Dr. Sotiris Valkaniotis. Dr. Valkaniotis has been using the open source softare mic-mac to compare pre- and post-earthquake satellite imagery. I will call this “pixel matching” analysis, or optical analysis.
Landsat-8 pixel tracking results (old school with Ampcor!) show a nice stepover in the Indonesia earthquake. This event gives a good perspective on why the valley in which Palu rests even exists in the first place
Synthetic Aperture Radar (SAR) is a remote sensing method that uses Radar to make observations of Earth. These observations include the position of the ground surface, along with other information about the material properties of the Earth’s surface. Line-of-sight deformation from ALOS-2 for the Palu earthquake (data provided by JAXA, processed using GMTSAR). Unwrapping is challenging for this earthquake! Some near-fault region is too decorrelated to be trustworthy.
#InSAR map of range or line-of-sight deformation of #PaluEarthquake from NASA Caltech-JPL analysis of JAXA ALOS-2 PALSAR-2 data acquired last week. Red areas moved west or down in this unwrapped interferogram, unreliable phase masked out. Star USGS epicenter.
#InSAR map of range or line-of-sight deformation of #PaluEarthquake from NASA Caltech-JPL analysis of JAXA ALOS-2 PALSAR-2 data acquired last week. Red areas moved west or down in this unwrapped interferogram, unreliable phase masked out. Star USGS epicenter.
There have been observations of tsunami waves recorded by tide gages installed at Pantoloan Port and Mumuju, Sulawesi. Locations are shown on the map above. A tsunami with a 10 cm wave height was recorded at Mumuju tide gage and a wave with a height of about 1.7 meters was recorded at Pantoloan tide gage. Learn more about the tsunami here. Landslides during and following the M=7.5 earthquake in central Sulawesi, Indonesia possibly caused the majority of casualties from this catastrophic natural disaster. Volunteers (citizen scientists) have used satellite aerial imagery collected after the earthquake to document the spatial extent and magnitude of damage caused by the earthquake, landslides, and tsunami. FOS = Resisting Force / Driving Force When FOS > 1, the slope is stable and when FOS < 1, the slope fails and we get a landslide. The illustration below shows these relations. Note how the slope angle α can take part in this ratio (the steeper the slope, the greater impact of the mass of the slope can contribute to driving forces). The real world is more complicated than the simplified illustration below.
Nowicki Jessee and others (2018) is the preferred model for earthquake-triggered landslide hazard. Our primary landslide model is the empirical model of Nowicki Jessee and others (2018). The model was developed by relating 23 inventories of landslides triggered by past earthquakes with different combinations of predictor variables using logistic regression. The output resolution is ~250 m. The model inputs are described below. More details about the model can be found in the original publication. We modify the published model by excluding areas with slopes <5° and changing the coefficient for the lithology layer "unconsolidated sediments" from -3.22 to -1.36, the coefficient for "mixed sedimentary rocks" to better reflect that this unit is expected to be weak (more negative coefficient indicates stronger rock).To exclude areas of insignificantly small probabilities in the computation of aggregate statistics for this model, we use a probability threshold of 0.002.
Zhu and others (2017) is the preferred model for liquefaction hazard. The model was developed by relating 27 inventories of liquefaction triggered by past earthquakes to globally-available geospatial proxies (summarized below) using logistic regression. We have implemented the global version of the model and have added additional modifications proposed by Baise and Rashidian (2017), including a peak ground acceleration (PGA) threshold of 0.1 g and linear interpolation of the input layers. We also exclude areas with slopes >5°. We linearly interpolate the original input layers of ~1 km resolution to 500 m resolution. The model inputs are described below. More details about the model can be found in the original publication.
Well, around 3 AM my time (northeastern Pacific, northern CA) there was a sequence of earthquakes including a mainshock with a magnitude M = 7.5. This earthquake happened in a highly populated region of Indonesia. I awakened this morning (my time, obviously) to find that there are over 380 reported deaths from this earthquake and tsunami. More on this later in the day (clouds are preparing to our and i need to put some of my stuff under tarps). Here is a (200 MB) video that I edited slightly. Download here. This was originally posted here. I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.0 in one version.
3D cartoon of plate boundaries in the Molucca Sea region modified from Hall et al. (1995). Although seismicity identifies a number of plates there are no continuous boundaries, and the Cotobato, North Sulawesi and Philippine Trenches are all intraplate features. The apparent distinction between different crust types, such as Australian continental crust and oceanic crust of the Philippine and Molucca Sea, is partly a boundary inactive since the Early Miocene (east Sulawesi) and partly a younger but now probably inactive boundary of the Sorong Fault. The upper crust of this entire region is deforming in a much more continuous way than suggested by this cartoon.
Regional geodynamic sketch that presents the present day deformation model of Sulawesi area (after Beaudouin et al., 2003) and four main deformation systems around the Central Sulawesi block, highlighting the tectonic complexity of Sulawesi. Approximate location of the Central Sulawesi block rotation pole (P) [compatible with both GPS measurements (Walpersdorf et al., 1998a) and earthquake moment tensor analyses (Beaudouin et al., 2003)], as well as the major active structures are reported. Central Sulawesi Fault System (CSFS) is formed by the Palu–Koro and Matano faults. Arrows correspond to the compression and/or extension directions deduced from both inversion and moment tensor analyses of the focal mechanisms; arrow size being proportional to the deformation rate (e.g., Beaudouin et al., 2003).We also represent the focal mechanism provided by the Harvard CMT database [CMT data base, 2005] for the recent large earthquake (Mw=6.2; 2005/1/23; lat.=0.92° S; long.=120.10° E). The box indicates the approximate location of the Fig. 6 that corresponds to the geological map of the Palu basin region. The bottom inset shows the SE Asia and Sulawesi geodynamic frame where arrows represent the approximate Indo-Australian and Philippines plate motions relative to Eurasia.
Sketch map of the Cenozoic Central Sulawesi fault system. ML represents the Matano Lake, and Leboni RFZ, the Leboni releasing fault zone that connects the Palu–Koro and Matano Faults. Triangles indicate faults with reverse component (triangles on the upthrown block). On this map are reported the fault kinematic measurement sites.
West-looking view of the Palu–Koro fault escarpment SSW of the Palu basin showing faceted spurs and a left-lateral offset of an alluvial fan. At the bottom, sketch of the photograph where white arrows point to the fault trace and black arrows point to the cumulate fan offset along the fault traces.
Simplified geological map of the Palu domain (modified after Sukamto, 1973) where are reported the locations of fission-track samples. 1 — Holocene alluvial deposits; 2 — Quaternary coral reef terraces; 3 — Mio-quaternary molasses, 4 — Mio-quaternary granitic rocks and granodiorites, 5 — Middle to Upper Eocene Tinombo Formation metamorphism, 6 — Tinombo Formation magmatism, 7 and 8 — metamorphic bedrock (7 — Cretaceous Latimonjong Formation; 8 — Triassic-Jurassic Gumbasa Formation).
The area of convergence of the Eurasian, Philippine and Australian plate is characterized by the Sula block motion. Active block boundaries are the North Sulawesi trench *(1)., the Palu-Koro (2), and the Matano (3) faults. The Palu transect is indicated buy the box, with a zoom presented in the inset. Furthermore, the two largest earthquakes (CMT) occurring during the observation period are indicated.
Velocities of the Palu transect stations, with respect to the PALU station. Error ellipses correspond to formal uncertainties of the global solution with a confidence level of 90%.
Transect station velocity components parallel to the fault, with the co-seismic deformation due to the Jan. 1996 earthquake removed. They are indicated in function of their distance to the fault. The dark grey line shows best model values (5.5 cm/yr total velocity, 12 km locking depth). Lighter grey lines correspond to locking depths of 8 and 16 km, marking an uncertainty of +-4 km.
GPS velocities of Sulawesi and surrounding sites with respect to the Sunda Plate. Grey arrows belong to the Makassar Block, black arrows belong to the northern half of Sulawesi, and white arrows belong to non-Sulawesi sites (99% confidence ellipses). Numbers near the tips of the vectors give the rates in mm/yr. The main tectonic structures of the area are shown as well.
Rotational part of the inferred velocity field in the Sulawesi area (relative to the Sunda Plate) as predicted by the Euler vectors of the best fit model (model 2). Error ellipses of predicted vectors show the 99% level of confidence. Also shown are poles of rotation and error ellipses (with respect to the Sunda Plate) from the best fit model. Curved arrows indicate the sense of rotation, and numbers indicate the rotation rate. MAKA, Makassar Block; MANA, Manado Block; ESUL, East Sula Block; NSUL, North Sula Block.
Best fit block model derived from both GPS and earthquakes slip vector azimuth data. Center: Observed (red) and calculated (green) velocities with respect to the Sunda Block (shown are 20% confidence ellipses, after GPS reweighting; see text). The slip rate deficit (mm/yr) for the faults included in the model is represented by a color bar. The profile of Figure 7 is located by the dashed black line. The black rectangles around Palu and Gorontalo faults localize the insets. Top right and bottom left insets show details of the measured and modeled velocities across the Gorontalo and Palu faults. The bottom right inset shows residual GPS velocities with respect to the model. The value of the coupling ratio, j, for the faults included in the model is represented by the color bar. Light blue dots represent the locations of the fault nodes where the coupling ratio is estimated. Nodes along the block boundaries are at the surface of the Earth, and the others are at depth along the fault plane. In this model, j is considered uniform along strike and depth for all the faults, except for Palu Fault and Minahassa Trench, where it is allowed to vary along strike.
Velocity profile across Makassar Trench, Palu Fault, and Gorontalo Fault (profile location in Figure 6) in Sunda reference frame. Observed GPS velocities are depicted by dots with 1-sigma uncertainty bars, while the predicted velocities are shown as curves. The profile normal component (approximately NNW) (i.e., the strike-slip component across the NW trending faults) is shown with black dots and solid line, while the profile-parallel component (normal or thrust component across the fault) is shown with grey dots and a dashed line. Where the profile crosses the faults and blocks is labeled.
(top) GPS velocities in Palu area relative to station WATA. STRM topography is used as background. (bottom) Four parallel elastic dislocations that fit best the velocities in the Palu fault zone. The fault-parallel component of the GPS velocities (with 1-sigma error bars) is plotted with respect to their distance to the main fault scarp, in the North Sula Block reference frame. The black curve represents the fault-parallel modeled velocity of the four strand model. For comparison, the fault-parallel modeled velocity predicted by the single fault model is also plotted (grey dashed curve). The location of the modeled dislocation is represented as vertical bars for each model (black and dashed grey lines, respectively).
Central Sulawesi overview digital elevation model (SRTM), CMT catalogue earthquakes, 35 km depth and structures that show geomorphic evidence of Quaternary tectonic activity. Rivers marked in white. Illumination from NE.
(a) The Palu and Sapu valleys showing structures that with geomorphic evidence of Quaternary tectonic activity, plus topography and drainage. Mountain front sinuosity values in bold italic text. For location, see Figure 4. Major drainage basins for Salo Sapu and Salo Wuno are marked, separated by uplift at the western end of the Sapu valley fault system. (b) View of the Palu–Koro Fault scarp from the Palu valley, showing geomorphic evidence of Quaternary tectonic activity.
Evidence of a cross-basin fault system within the Palu valley Quaternary fill. (a) Overview ASTER digital elevation model draped with ESRI imagery layer. Illumination from NW. Palu River channels traced from six separate images from 2003 to 2015. Inset shows fault pattern developed in an analogue model of a releasing bend, modified after Wu et al. (2009), reflected and rotated to mimic the Palu valley. Sidewall faults and cross-basin fault system are highlighted in the model and on the satellite imagery. (b, c) Laterally confined meander belts, interpreted as representing minor subsidence within the cross-basin fault system. (d) Laterally confined river channels directly along-strike from a Palu–Koro Fault strand seen to offset alluvial fans in the south of the valley. (c, d, e) showESRI imagery.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
#Earthquake_alert [UPDATE] – The spread of #epicenters of #Donggala #earthquake on Sep 28, 2018. Map obtained from EMSC App with a slight modification. C.c. @EricFielding @seismo_steve @patton_cascadia @janinekrippner #Indonesia #earthquake #alert #warning #mitigation #Sulawesi pic.twitter.com/NOMPtBBr1B — Desianto F. Wibisono (@TDesiantoFW) September 28, 2018 BREAKING: Video shows tsunami hitting the Indonesian city of Palu pic.twitter.com/XCXXHZwAtu — BNO News (@BNONews) September 28, 2018 This footage shows the catastrophic moment when #tsunami hit the city of Palu after 7.7 magnitude #earthquake shook the city this evening. #prayforpalu #prayforindonesia pic.twitter.com/I8JBi4dZjz — Ramadhani Eko P (@ramadhaniep) September 28, 2018 First motion mechanism: Mwp7.2 #earthquake Minahassa Peninsula, Sulawesi https://t.co/kCIw9Vypa6 pic.twitter.com/PAAwEM8mGX — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) September 28, 2018 News on major western channels is starting to show up… 4 hours after the earthquake…https://t.co/lcm521Hx1f — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) September 28, 2018 Source model by @geoscope_ipgp @IPGP_officiel confirms magnitude (Mw7.5) and left-lateral strike-slip mechanism for #earthquake on Palu-Koro FZ #Sulawesi, #Indochina. Hypocenter depth estimate 18-25km.https://t.co/4AvAbHbo4Q pic.twitter.com/G22EAbo5Bc — Robin Lacassin (@RLacassin) September 28, 2018 Left lateral movement along the Palu-Koro fault shown by GPS (figure from Walpersdorf et al. 1998) consistent with NNW nodal plane of Mw 7.4 mainshock focal mechanism. pic.twitter.com/i0Cid1jIyl — JD Dianala (@geoloJD) September 28, 2018 Back Projection for Mw 7.5 MIZAHASSA PENINSULA #EARTHQUAKE, SULAWESI https://t.co/wxc1fnAGWQ #SulawesiTengah pic.twitter.com/RdEfD50Xkz — IRIS Earthquake Sci (@IRIS_EPO) September 28, 2018 Its so close to my city. After earthquakes then we attack by tsunami again. Please pray for us :( #PrayForDonggala #Gempa pic.twitter.com/9Q7fWBuOer — ★ ghy ★ (@ksjnoona) September 28, 2018 Interesting difference between locations of aftershocks of M7.5 Palu earthquake in black and the foreshocks in purple pic.twitter.com/hO7wGh8Cq6 — Jascha Polet (@CPPGeophysics) September 28, 2018 Analisis sementara ahli tsunami dsri ITB berdasarkan modeling dan kajian sebelumnya bahwa tsunami di Palu disebabkan adanya longsoran bawah laut saat gempa 7,7 SR mengguncang Donggala. Teluk Palu dan pesisir Donggala memang rawan tsunami. Masih dilakukan kajian lagi. pic.twitter.com/1YbHEFmTfT — Sutopo Purwo Nugroho (@Sutopo_PN) September 29, 2018 Potential #tsunami impact #Palu, #Minahasa, #Sulawesi, after very strong #earthquake. Based on adjusted @USGS finite fault model and video footage. Numerical model, no observation(!) Any news on wave heights around #Baya or #Mapaga? @UKEQ_Bulletin @JuskisErdbeben @patton_cascadia pic.twitter.com/jF5DP4saL9 — CATnews (@CATnewsDE) September 28, 2018 Analisis sementara ahli tsunami dsri ITB berdasarkan modeling dan kajian sebelumnya bahwa tsunami di Palu disebabkan adanya longsoran bawah laut saat gempa 7,7 SR mengguncang Donggala. Teluk Palu dan pesisir Donggala memang rawan tsunami. Masih dilakukan kajian lagi. pic.twitter.com/1YbHEFmTfT — Sutopo Purwo Nugroho (@Sutopo_PN) September 29, 2018 M7.5 #earthquake and #aftershocks in #Indonesia as detected by the #RaspberryShake #CitizenScience community network. See https://t.co/hbr1xPdgFN and https://t.co/iYdJRU3iub for more details. #Palu #Sulawesi #Philippines #Malaysia pic.twitter.com/WskgV2VNiK — Raspberry Shake (@raspishake) September 28, 2018 I am pretty sure the #tsunami video is at -0.8821, 119.841 – see images. This is part of the waterfront at #Palu. If I am right, and assuming the video was shot today, then it appears that we have a significant tsunami at this location at least. pic.twitter.com/J6boTUrrcm — Dave Petley (@davepetley) September 28, 2018 Donggala as a 7.7 magnitude #earthquake with #tsunami warning occured recently in north of #Palu Sulawesi . #PrayForDonggala 🙏🏼🇮🇩 pic.twitter.com/vcx83UtOlC — Zabihullah Najafi (@zabinajafi) September 28, 2018 Full Video. Semoga Allah SWT memberikan keselamatan dan ketabahan untuk saudara-saudara kita di Sulawesi Tengah. 🙏🏼 — Anggunesia (@Anggunesia) September 28, 2018 #Palu before and after tsunami pic.twitter.com/MdxICg2oC0 — ROBERT VINOD (@RobertVinod) September 28, 2018 Jembatan Palu IV destroyed by the earthquake in #Palu, Central Sulawesi.#gempa #tsunami pic.twitter.com/Q8PKwvE5Hj — Matthew Lanier (@PakMamat) September 28, 2018 Incredible and scary #tsunami video from #Palu, #Indonesia Through google maps I found where it was shot as multiple tsunami waves funneled north to south down a long narrow bay into Palu Shopping district on the beach. Devastating and tragic pic.twitter.com/RIogOlP0IR — Michael Seger (@MichaelSeger) September 28, 2018 Our prayers are always with #Indonesia May Allah help all the brothers and sisters who are suffering because of #earthquake and #tsunami which happened few hours ago. #palu #donggala #prayfordonggala pic.twitter.com/gdVzzMZ6uF — M.Abdulhakim Mahmout (@ahmahmout) September 28, 2018 Another video at moment of #Sunami at #Palu #Sulawesi in Indonesia — Andrea Legarreta (@AndeaLegarreta) September 28, 2018 In a video that appeared to be taken at night, doctor Komang Adi Sujendra said 30 people were killed and had been taken to the hospital.https://t.co/I4fko9mvwo#Quake #Indonesia #Palu #Sulawesi #Tsunami — New Straits Times (@NST_Online) September 29, 2018 The Indonesian news-agency Kompas, states that the Agency for Meteorology, Climatology and Geophysics (BMKG) has said that a 1.5-2m. #Tsunami have hit the areas of #Palu #donggala and #Mamuju — Øystein L. Andersen (@OysteinLAnderse) September 28, 2018 Amazing! Did surface fault rupture pass under (and destroy) Palu Bridge IV? Apparent left-lateral offset of bridge ~~5m in still from video. M7.5 #earthquake #Palu #Indonesiahttps://t.co/Oirdl1oOPE pic.twitter.com/8licQbUufz — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) September 29, 2018 Earthquake triggering a tsunami and likely more shocks in Indonesia | https://t.co/1twVj9F84q https://t.co/tChjMILSd9 via #NSFfunded @temblor #earthquakes #temblor — temblor (@temblor) September 29, 2018 Kondisi jembatan Ponulele di Kota Palu yang hancur akibat gempa 7,7 SR. Jembatan ini sebelumnya sebagai icon Kota Palu. Kondisinya hancur. Pascagempa tsunami menerjang pantai sekitarnya. Permukiman di bawah hancur dan terbawa tsunami. pic.twitter.com/4XrLrzHp1a — Sutopo Purwo Nugroho (@Sutopo_PN) September 28, 2018 BBC News – Indonesia earthquake: Hundreds dead in Palu quake and tsunami https://t.co/r4qnOv6Be6 — patton_cascadia (@patton_cascadia) September 29, 2018 SITUATION UPDATE No. 1 – Sulawesi Earthquake – 29 September 2018 – Our deepest condolences for the affected communities in Sulawesi especially in #Donggala and #Palu. Stay tuned to official channels for further information https://t.co/2dLFwj3Crw … #bnpb #gempa #tsunami pic.twitter.com/toJ08oKBr8 — AHA Centre (@AHACentre) September 29, 2018 From colleagues in #Palu #centralsulawesi following yesterday’s #earthquake and #tsunami 🙏😢 pic.twitter.com/p451qx3ELq — Richard Woods (@RichardWoodsNZ) September 29, 2018 #Peringatan Dini Tsunami di SULTENG,SULBAR, Gempa Mag:7.7, 28-Sep-18 17:02:44WIB, Lok:0.18LS,119.85BT,Kdlmn:10Km#BMKG pic.twitter.com/V9FLnJbdhs — BMKG (@infoBMKG) September 28, 2018 Zoomed in around shoreline. pic.twitter.com/nMJ7oICQmE — Murray Ford (@mfordNZ) September 29, 2018 Quick & rough subpixel optical correlation for images above, using MicMac (no scale or georef), 2D displacement on NS axis. Red is movement towards north, blue towards south. pic.twitter.com/ueUbVxT4Qe — Sotiris Valkaniotis (@SotisValkan) September 29, 2018 From colleagues in #centralsulawesi following yesterday’s #earthquake and #tsunami 🙏😢 #Palu #Donggala pic.twitter.com/hit2B7ZD7V — Richard Woods (@RichardWoodsNZ) September 29, 2018 Aerial photos of #tsunami and #earthquake damage in #Palu have been released by #Indonesia's disaster management agency @BNPB_Indonesia pic.twitter.com/vXtGxa8UZx — Richard Woods (@RichardWoodsNZ) September 29, 2018 Aerial photos of #tsunami and #earthquake damage in #Palu have been released by #Indonesia's disaster management agency @BNPB_Indonesia pic.twitter.com/nhxoPk27Rj — Richard Woods (@RichardWoodsNZ) September 29, 2018 Perhatikan baik² video pasca Gempa Sulawesi ini. Ada 4 point yg bisa kita liat, utk menilai betapa bikin merindingnya dampak gempa ini pic.twitter.com/rFvtnzotIs — Eling Lan Waspada (@Jogja_Uncover) September 29, 2018
Back to the Earthquake Reports page. Well well. Both types of triggering impart a very very small amount of increased stress on a given fault or fault system. This means that the way for an earthquake to be triggered in this manner, the potentially triggered fault will need to be on the verge of rupturing on its own. The stresses released by earthquakes are much larger than those stresses imparted by dynamic or static triggering, so the faults need to be “ready to go” if they are to be triggered. I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.0 in one version.
Tectonic map of the Lesser Sunda Islands, showing the main tectonic units, main faults, bathymetry and location of seismic sections discussed in this paper.
This plot shows the earthquake localizations on a South-North cross section for the lat -14°/-4° long 114°/124° quadrant corresponding to the Lesser Sunda Islands region. The localizations are extracted from the USGS database and corresponds to magnitude greater than 4.5 in the 1973-2004 time period (shallow earthquakes with undetermined depth have been omitted.
Six 15 km deep seismic sections acquired by BGR from west to east traversing oceanic crust, deep sea trench, accretionary prism, outer arc high and fore-arc basin, derived from Kirchoff prestack depth migration (PreSDM) with a frequency range of 4-60 Hz. Profile BGR06-313 shows exemplarily a velocity-depth model according to refraction/wide-angle
Tectonic and geographic map of the eastern Sunda arc and vicinity. Active volcanoes are represented by triangles, and bathymetric contours are in kilometers. Thrust faults are shown with teeth on the upper plate. The dashed box encloses the study area.
Cartoon cross section of Timor today, (cf. Richardson & Blundell 1996, their BIRPS figs 3b, 4b & 7; and their fig. 6 gravity model 2 after Woodside et al. 1989; and Snyder et al. 1996 their fig. 6a). Dimensions of the filled 40 km deep present-day Timor Tectonic Collision Zone are based on BIRPS seismic, earthquake seismicity and gravity data all re-interpreted here from Richardson & Blundell (1996) and from Snyder et al. (1996). NB. The Bobonaro Melange, its broken formation and other facies are not indicated, but they are included with the Gondwana mega-sequence. Note defunct Banda Trench, now the Timor TCZ, filled with Australian continental crust and Asian nappes that occupy all space between Wetar Suture and the 2–3 km deep deformation front north of the axis of the Timor Trough. Note the much younger decollement D5 used exactly the same part of the Jurassic lithology of the Gondwana mega-sequence in the older D1 decollement that produced what appears to be much stronger deformation.
Comparison of hypocentral profiles across the (a) Java subduction zone and (b) Timor collision zone (paleo-Banda trench). Catalog compiled from multiple reporting agencies listed in Table 1. Events of Mw>4.0 are shown for period 1815 to 2015.
Location of SeaMARC II survey (Plate 1 and Figures 2) and geographic features discussed in text. Triangles on upper plates of thrust zones.
Bathymetry, faults, and mud diapirs of the central Flores thrust zone, based on interpretation of SeaMARC II data and seismic reflection profiles. Shown also are locations (circled numbers) of all seismic profiles. Mud diapirs are solid black. Triangles on upper plates of thrust faults.
Illustration of major tectonic elements in triple junction geometry: tectonic features labeled per Figure 1; seismicity from ISC-GEM catalog [Storchak et al., 2013]; faults in Savu basin from Rigg and Hall [2011] and Harris et al. [2009]. Purple line is edge of Australian continental basement and fore arc [Rigg and Hall, 2011]. Abbreviations: AR = Ashmore Reef; SR = Scott Reef; RS = Rowley Shoals; TCZ = Timor Collision Zone; ST = Savu thrust; SB = Savu Basin; TT = Timor thrust; WT =Wetar thrust; WASZ = Western Australia Shear Zone. Open arrows indicate relative direction of motion; solid arrows direction of vergence.
(a) Focal mechanism solutions for the study region. The focal mechanisms are classified based on depth intervals to illustrate the style of faulting within the different structural domains. Note (b) sinistral reverse motion along Timor trough, (c) subduction related pattern along Java trench, and dextral solutions along the western Australia extended margin (Figure 4a) north of 20°S. Centroid moment tensor (CMT) solutions [Dziewonski et al., 1981] are from the CMT project [Ekström et al., 2012; http://www.globalcmt.org/CMTcite.html] for events of Mw>5.0 for the period 1976 onward.
GPS velocities of Sunda and Banda arc region. Large black and grey arrow shows motion of Australia relative to Eurasia [DeMets et al., 1994]. Thin black arrows show GPS velocities of Sunda and Banda arc regions relative to Australia [Nugroho et al., 2009]. Seismicity from ISC-GEM catalog [Storchak et al., 2013]. Note reduction of station velocities from west to east indicating progressive coupling of the Banda arc to the Australian plate compared to the area along the Sunda arc.
Seismotectonic setting of the Sunda-Banda arc-continent collision, East Indonesia. Major faults (thick black lines) [Hamilton, 1979]. Topography and bathymetry are from Shuttle Radar Topography Mission (http://topex.ucsd.edu/www_html/srtm30_plus.html). Focal mechanisms are from the Global Centroid Moment Tensor. Blue mechanisms correspond to earthquakes with Mw>7 (brown transparent ellipses are the corresponding rupture areas for Flores 1992 and Alor 2004 earthquakes), while the green focal mechanism shows the highest magnitude recorded in Sumbawa. Red dots indicate the locations of major historical earthquakes [Musson, 2012].
GPS velocities determined in this study with respect to Sunda Block. Uncertainty ellipses represent 95% confidence level. The inset figure corresponds to the area of the dashed rectangle in the map. Light blue arrows show the velocities for East and West Makassar Blocks.
Relative slip vectors across block boundaries, derived from our best fit model. Arrows show motion of the hanging wall (moving block) relative to the footwall (fixed block) with 95% confidence ellipses. The tails of arrows is located within the “moving” block. Black thick lines show well-defined boundaries we use as active faults in our model and dashed lines show less well-defined boundaries (green : free-slipping boundaries and black: fixed locked faults) . Principal axes of the horizontal strain tensor estimated for the SUMB, EMAK, and EJAV are shown in pink. The thick pink arrow shows the relative motion of Australia with respect to Sunda (AUST/SUND). Abbreviations are Sumba Block (SUMB), West Makassar Block (WMAK), East Makassar Block (EMAK), East Java Block (EJAV), and Timor Block (TIMO). The background seismicity is from the International Seismological Centre catalog with magnitudes ≥5.5 and depths <40 km.
Fault slip rate components: (a) fault normal (extension positive) and (b) fault parallel (right-lateral positive).
Depth of burial as a function of fault length/width (L/W) ratio for some well-studied thrust faults. Burial depth is normalized by the vertical extent of the fault, as shown in the inset. Large subduction earthquakes tend to locate in the upper right; moderate size continental thrust faults tend to locate to the left. Sources are listed in the paper.
Cross sections (left) through the center and (right) beyond the end of the fault of a 45°-dipping thrust source fault. Optimally oriented receiver thrust planes are shown in areas of increased Coulomb stress. Both the 1971 San Fernando and 1994 Northridge faults dip about 45°. (a) The surface cutting thrust (Mw = 7.0) drops the stress in the upper crust, (b) whereas a blind thrust (Mw = 6.8) increases the stress over much of the upper crust, despite its smaller magnitude. Near-surface regions of stress increase are sometimes relieved by secondary surface faulting, as occurred in the Northridge shock. (c) Stress changes caused by blind and surface fault slip. (d–f ) Beyond the ends of the faults the stress distribution is relatively insensitive to whether the thrust is surface-cutting or blind, where the along strike projection of faults is dotted.
Stress change caused by the 1 October 1987 Mw = 6.0 Whittier Narrows earthquake. (a) Map view of maximum stress change for depth range of 10.0–14.4 km, with seismicity (1 October 1987 to 31 December 1994, M ≥ 1.0, horizontal error <0.5 km) from Shearer [1997] for the same depth range. The source fault model, shown by the black inscribed line, has tapered thrust slip on a 4.5 X 4.5 km fault with strike 270°, dip 25°, and rake 90°, following Lin and Stein [1989]; receiver faults are assumed to have the same parameters. (b) Coulomb stress change in cross section cutting the center of the fault. The resulting stress component is shown in the top left-hand corner. (c) Normal stress change. Unclamping is positive. There were no earthquakes recorded during 1975–1987 at the minimum catalog magnitude of M ≥ 0.8 [Richards-Dinger and Shearer, 2000], and so the aftershock pattern is more likely a response to the stress changes imparted by the main shock than a continuation of the background seismicity.
Cross-sectional areas across the midpoint of a thrust fault, showing stresses imparted by a 30°-dipping blind thrust source fault on nearby (a, b) reverse and (c, d) strike-slip receiver faults. The pattern of stress change on strike-slip receiver faults differs markedly for long (Figure 5c) and short (Figure 5d) source faults. Strike-slip faulting is also enhanced above a blind thrust fault (Figure 5d). These cross sections can be compared with the map view for the same cases in Figure 4.
Deformation of Lombok Island, Indonesia due to 5 August 2018 earthquake shows uplift of northwest corner due to fault slip at depth, measured with #InSAR of Copernicus Sentinel-1 radar images processed by Caltech-JPL ARIA project. Data at https://go.nasa.gov/2OlbxY6
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
FirstMoMech: M6.8-7.0 #earthquake #Lombok, Sumbawa Region, Indonesia https://t.co/kCIw9Vypa6 pic.twitter.com/ySoFdeqk81 — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) August 19, 2018 Info #Gempa Mag:7.0, 19-Aug-18 21:56:27 WIB, Lok:8.28 LS,116.71 BT (30 km TimurLaut LOMBOKTIMUR-NTB), Kedlmn:10 Km ::BMKG pic.twitter.com/lgoks1FvN2 — MAGMA Indonesia (@id_magma) August 19, 2018 M6.9 #earthquake #Lombok #Indonesia 20min ago (lower) looks slighly smaller than Aug 5 M6.9 mainshock (upper). M6.3 event earlier today (middle). Seismograms at Christmas Island 1200km west of #Lombok, with same amplitude scale.https://t.co/KoqUgsayO3 pic.twitter.com/A1z33WVuL3 — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) August 19, 2018 Updated seismicity map of the Lombok sequence. Earthquakes line up along an East-West striking fault zone of 100+ km length. Black circles are events after August 5th. pic.twitter.com/LXdiR8m3HE — Jascha Polet (@CPPGeophysics) August 19, 2018 The Powerful Earth https://t.co/Iw3kYOm7W5 pic.twitter.com/EPZ9FjcsTB — TXESP (@KristiFinkTXESP) August 19, 2018 News in from Mt. Rinjani #lombokearthquake pic.twitter.com/vHKrxEP62y — Gillian McKinon (@GKinon) August 19, 2018 Mount Rinjani! What is happening? #lombokearthquake pic.twitter.com/7WrvDKCYRI — Gillian McKinon (@GKinon) August 19, 2018 We have to move our tent because the electricity pole almost falls down. We need to calm down the children. Currently no electricity. #earthquake #gempa #lombok #earthquakelombok #gempalombok #pedulianak #children #charity pic.twitter.com/YC4Um5pPkz — Peduli Anak (@pedulianak) August 19, 2018 This is North Lombok today….speechless…. More photos >> https://t.co/Rt5xdYG4GJ#earthquake #gempa #lombok #earthquakelombok #gempalombok #lombokearthquakerelief pic.twitter.com/256M0EH0Oy — Peduli Anak (@pedulianak) August 19, 2018 We just arrived in Rempek village, North Lombok, and already couple small earthquakes greeted us. It looks like no single house is standing :(#earthquake #gempa #lombok #earthquakelombok #gempalombok #lombokearthquakerelief #lombokstrong #lombokbangkit #rebuild #pedulianak pic.twitter.com/4AtTpKCQKh — Peduli Anak (@pedulianak) August 19, 2018 Pool overflowing #earthquake #earthquakelombok pic.twitter.com/vJcvjf2RUO — Andrew Bartram (@barty_of_Aus) August 19, 2018 Indonésie : pourquoi y a-t-il autant de séismes à Lombok ? https://t.co/TB1pUZp1Em via @europe1 avec @RLacassin et @KlingerYann. J'adore comment l'un est "chercheur" et l'autre "géologue" 😉 — Dr. Lucile Bruhat (@seismolucy) August 20, 2018 Preliminary look at NASA Caltech-JPL ARIA interferogram for 19 August M6.9 East Lombok earthquake from Copernicus Sentinel-1 data acquired 14 and 20 August. Color contours are 2.8 cm (1.2) inches each, showing uplift on NE corner of island. More soon. pic.twitter.com/klsGSB2BRe — Eric Fielding (@EricFielding) August 21, 2018 NASA Caltech-JPL ARIA displacement map for 19 August M6.9 East Lombok earthquake processed from Copernicus Sentinel-1 #InSAR data, shows around 30 cm uplift of NE corner of island. Fault rupture is east of fault ruptured in 5 August M6.9 quake pic.twitter.com/hBkXhBAKsh — Eric Fielding (@EricFielding) August 22, 2018 The cascading series of earthquakes that struck #Lombok in a span of three weeks is unique and rarely seen. Read the commentary by EOS Research Fellow Dr Muzli on @ChannelNewsAsia. https://t.co/r2gsYhq6ZO — Earth Observatory SG (@EOS_SG) September 3, 2018
Yesterday morning, as I was recovering from working on stage crew for the 34th Reggae on the River (fundraiser for the non profit, the Mateel Community Center), I noticed on social media that there was an M 6.9 earthquake in Lombok, Indonesia. This is sad because of the likelihood for casualties and economic damage in this region. Based on Eric Fielding and JD Dianala’s interpretation of the InSAR data, the M 6.4 and M 6.9 earthquakes could possibly have a similar hypocentral depth. See Social Media update below. People have been asking me if we might expect another large or larger earthquake in this region. So, here is what I have told them: I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.0 in one version.
Tectonic and geographic map of the eastern Sunda arc and vicinity. Active volcanoes are represented by triangles, and bathymetric contours are in kilometers. Thrust faults are shown with teeth on the upper plate. The dashed box encloses the study area.
Cartoon cross section of Timor today, (cf. Richardson & Blundell 1996, their BIRPS figs 3b, 4b & 7; and their fig. 6 gravity model 2 after Woodside et al. 1989; and Snyder et al. 1996 their fig. 6a). Dimensions of the filled 40 km deep present-day Timor Tectonic Collision Zone are based on BIRPS seismic, earthquake seismicity and gravity data all re-interpreted here from Richardson & Blundell (1996) and from Snyder et al. (1996). NB. The Bobonaro Melange, its broken formation and other facies are not indicated, but they are included with the Gondwana mega-sequence. Note defunct Banda Trench, now the Timor TCZ, filled with Australian continental crust and Asian nappes that occupy all space between Wetar Suture and the 2–3 km deep deformation front north of the axis of the Timor Trough. Note the much younger decollement D5 used exactly the same part of the Jurassic lithology of the Gondwana mega-sequence in the older D1 decollement that produced what appears to be much stronger deformation.
Comparison of hypocentral profiles across the (a) Java subduction zone and (b) Timor collision zone (paleo-Banda trench). Catalog compiled from multiple reporting agencies listed in Table 1. Events of Mw>4.0 are shown for period 1815 to 2015.
Location of SeaMARC II survey (Plate 1 and Figures 2) and geographic features discussed in text. Triangles on upper plates of thrust zones.
Bathymetry, faults, and mud diapirs of the central Flores thrust zone, based on interpretation of SeaMARC II data and seismic reflection profiles. Shown also are locations (circled numbers) of all seismic profiles. Mud diapirs are solid black. Triangles on upper plates of thrust faults.
Illustration of major tectonic elements in triple junction geometry: tectonic features labeled per Figure 1; seismicity from ISC-GEM catalog [Storchak et al., 2013]; faults in Savu basin from Rigg and Hall [2011] and Harris et al. [2009]. Purple line is edge of Australian continental basement and fore arc [Rigg and Hall, 2011]. Abbreviations: AR = Ashmore Reef; SR = Scott Reef; RS = Rowley Shoals; TCZ = Timor Collision Zone; ST = Savu thrust; SB = Savu Basin; TT = Timor thrust; WT =Wetar thrust; WASZ = Western Australia Shear Zone. Open arrows indicate relative direction of motion; solid arrows direction of vergence.
(a) Focal mechanism solutions for the study region. The focal mechanisms are classified based on depth intervals to illustrate the style of faulting within the different structural domains. Note (b) sinistral reverse motion along Timor trough, (c) subduction related pattern along Java trench, and dextral solutions along the western Australia extended margin (Figure 4a) north of 20°S. Centroid moment tensor (CMT) solutions [Dziewonski et al., 1981] are from the CMT project [Ekström et al., 2012; http://www.globalcmt.org/CMTcite.html] for events of Mw>5.0 for the period 1976 onward.
Topographic and tectonic map of the Indonesian archipelago and surrounding region. Labeled, shaded arrows show motion (NUVEL-1A model) of the first-named tectonic plate relative to the second. Solid arrows are velocity vectors derived from GPS surveys from 1991 through 2001, in ITRF2000. For clarity, only a few of the vectors for Sumatra are included. The detailed velocity field for Sumatra is shown in Figure 5. Velocity vector ellipses indicate 2-D 95% confidence levels based on the formal (white noise only) uncertainty estimates. NGT, New Guinea Trench; NST, North Sulawesi Trench; SF, Sumatran Fault; TAF, Tarera-Aiduna Fault. Bathymetry [Smith and Sandwell, 1997] in this and all subsequent figures contoured at 2 km intervals.
GPS velocities of Sunda and Banda arc region. Large black and grey arrow shows motion of Australia relative to Eurasia [DeMets et al., 1994]. Thin black arrows show GPS velocities of Sunda and Banda arc regions relative to Australia [Nugroho et al., 2009]. Seismicity from ISC-GEM catalog [Storchak et al., 2013]. Note reduction of station velocities from west to east indicating progressive coupling of the Banda arc to the Australian plate compared to the area along the Sunda arc.
Seismotectonic setting of the Sunda-Banda arc-continent collision, East Indonesia. Major faults (thick black lines) [Hamilton, 1979]. Topography and bathymetry are from Shuttle Radar Topography Mission (http://topex.ucsd.edu/www_html/srtm30_plus.html). Focal mechanisms are from the Global Centroid Moment Tensor. Blue mechanisms correspond to earthquakes with Mw>7 (brown transparent ellipses are the corresponding rupture areas for Flores 1992 and Alor 2004 earthquakes), while the green focal mechanism shows the highest magnitude recorded in Sumbawa. Red dots indicate the locations of major historical earthquakes [Musson, 2012].
GPS velocities determined in this study with respect to Sunda Block. Uncertainty ellipses represent 95% confidence level. The inset figure corresponds to the area of the dashed rectangle in the map. Light blue arrows show the velocities for East and West Makassar Blocks.
Relative slip vectors across block boundaries, derived from our best fit model. Arrows show motion of the hanging wall (moving block) relative to the footwall (fixed block) with 95% confidence ellipses. The tails of arrows is located within the “moving” block. Black thick lines show well-defined boundaries we use as active faults in our model and dashed lines show less well-defined boundaries (green : free-slipping boundaries and black: fixed locked faults) . Principal axes of the horizontal strain tensor estimated for the SUMB, EMAK, and EJAV are shown in pink. The thick pink arrow shows the relative motion of Australia with respect to Sunda (AUST/SUND). Abbreviations are Sumba Block (SUMB), West Makassar Block (WMAK), East Makassar Block (EMAK), East Java Block (EJAV), and Timor Block (TIMO). The background seismicity is from the International Seismological Centre catalog with magnitudes ≥5.5 and depths <40 km.
Fault slip rate components: (a) fault normal (extension positive) and (b) fault parallel (right-lateral positive).
Deformation of Lombok Island, Indonesia due to 5 August 2018 earthquake shows uplift of northwest corner due to fault slip at depth, measured with #InSAR of Copernicus Sentinel-1 radar images processed by Caltech-JPL ARIA project. Data at https://go.nasa.gov/2OlbxY6
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Expert warns of strong aftershocks in Indonesia following Lombok quakehttps://t.co/sEJyziJO1b pic.twitter.com/LtwwKLcsF7 — BBC News (World) (@BBCWorld) August 6, 2018 Mw=6.9, SUMBAWA REGION, INDONESIA (Depth: 18 km), 2018/08/05 11:46:34 UTC – Full details here: https://t.co/jws7oFBoaM pic.twitter.com/AtlFwTFCZa — Earthquakes (@geoscope_ipgp) August 5, 2018 M6.9 #earthquake #Lombok, #Indonesia: High-frequency seismogram (lower; station JAGI on Java ~250km W of epicenter) suggests up to ~50sec of rupture duration. Geoscope and USGS long-period waveform analyses give ~20sec duration.https://t.co/F8EkNdVkfYhttps://t.co/0fVh9lO59J pic.twitter.com/enJn9nYwUF — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) August 7, 2018 Do you believe in seismic gaps ?!! the location of the Mw 6.9 Lombok earthquake 2018 added to fig1 of our GRL 2016 paper pic.twitter.com/VXHWC7Mzop — Achraf (@KoulaliAchraf) August 6, 2018 Great @ESA_EO #Sentinel1 coverage of M6.9 #Loloan quake, Indonesia. Automatic @UAFGI #SARVIEWS InSAR 🛰️ data shows significant deformation. Download free InSAR data products for this event @ https://t.co/OfHXvqNlu6.@InSARinfo @Ak_Satellite @NASAEarthData pic.twitter.com/SkQ17k5gAT — Franz J Meyer (@SARevangelist) August 6, 2018 Watch the waves from the M6.9 #LombokEarthquake roll across the USArray seismic network (https://t.co/RIcNz4bgWq). Red means the ground is going up; blue means down. The waves are too small to be felt but can be detected by these sensitive instruments. https://t.co/SoZMmJHvCU pic.twitter.com/G66CUjeZqE — IRIS Earthquake Sci (@IRIS_EPO) August 6, 2018 2018-08-05 Mw6.9 Indonesia earthquake interferogram#insar #earthquake pic.twitter.com/al2ahJJ4pJ — R P (@rusi_p) August 6, 2018 Here are high-frequency estimates of apparent rupture duration for large earthquakes 1992-2012 compared to Global CMT (Lomax & Michelini, 2012). — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) August 7, 2018 Q: What is the probability that an #earthquake is a foreshock to a larger earthquake? — IRIS Earthquake Sci (@IRIS_EPO) August 7, 2018 Here is a coseismic interferogram of the Mw6.9 earthquake in Lombok island on Aug. 5. Analysis of Sentinel-1A/B images with Gamma(R) pic.twitter.com/tlJJT7Lx6i — 橋本学 (@manabu0131dpri) August 7, 2018 Mechanism & epicenter of today’s M6.9 quake in Lombok, Indonesia, similar to that of M6.4 week earlier (for which map & crosssection of historical seismicity attached), although bit deeper. Event likely did not occur on subduction interface, but on backthrust behind it. pic.twitter.com/2yMPIrwFcX — Jascha Polet (@CPPGeophysics) August 5, 2018 close-up view on #Lombok #earthquake, also covering #Bali, still expecting extensive damage and fatalities. Be prepared for various (strong) aftershocks. pic.twitter.com/1prVkTzNOr — CATnews (@CATnewsDE) August 5, 2018 #RT Several major #earthquakes have struck the Indonesian island of #Lombok in the past week. #Indonesia sits along the “Pacific Ring of Fire” where several #tectonicplates collide but there are other unique conditions around Lombok @ConversationUS ➡️ https://t.co/a4a6cCXnxl pic.twitter.com/Ir1YRFijHX — Raspberry Shake (@raspishake) August 7, 2018 Earthquake: Aug-06 M6.9 Pulau Lombok, Indonesia | depth 31 Km, ~100 people dead. Damage as far away as Bali. Mass evacuation 'chaos' from the Gili "tourist" Islands.#Lombokquake #ahemQUAKEShttps://t.co/b1P3wdq8nd — aHEMagain ❌ (@aHEM_again) August 6, 2018 #Indonesia’s National Disaster Management Agency released video of thousands of tourists trying to get off #Gili Islands after #Lombokquake. pic.twitter.com/ZXOW1aqpuQ — Jon Williams (@WilliamsJon) August 6, 2018 All trapped tourists have been evacuated from #Lombok's nearby Gili Meno Island after deadly earthquake, according to Indonesia's Tourism Ministry #Lombokquake pic.twitter.com/I2AofMLe3v — CGTN (@CGTNOfficial) August 7, 2018 Some of the damage at Teluk Nara bus station #Lombokquake pic.twitter.com/x4EkCLaFxP — David Lipson (@davidlipson) August 6, 2018 #Lombokquake M 7.0 which struck Lombok, Indonesia on 5 August 2018, caused small tsunamis. Death toll: 82 — Bali Promotion Center💅 (@translatorbali) August 6, 2018 The shoes of those trapped under this collapsed mosque #Lombokquake pic.twitter.com/mKNIAWJz9y — David Lipson (@davidlipson) August 7, 2018 #Lombokquake: Thousands evacuated after dozens die on #Indonesia island https://t.co/lIXD7vBENe — Ekanem Etim-Offiong (@akemmapapa) August 6, 2018 Tourists flee Indonesia's Lombok island after earthquake kills 98 #Lombokquake #Indonesia https://t.co/DxFlg7Mch3 — RangerRick ن (@sacreole) August 6, 2018 There's no scale, and actual modeling would show more precisely, but just comparing the number fringes from the InSAR by @rusi_p , it seems that there shouldn't be a very big difference in the depths of both earthquakes? https://t.co/xM1heCiXyg — JD Dianala (@geoloJD) August 7, 2018 USGS closest station JAGI is ~250km from epicenter (need stations at distance of approx true depth to resolve depth well) and residuals at nearer stations are very large (>1sec). So event depth is likely very poorly constrained.https://t.co/gU9lOgE4vp pic.twitter.com/g2gsVsgA1s — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) August 8, 2018 Displacement map for 5 August 2018 M6.9 #Lombok #earthquake from Copernicus Sentinel-1 radar data #InSAR processed by NASA Caltech-JPL ARIA released on @NASAJPL news page https://t.co/YXv2BzVHgu — Eric Fielding (@EricFielding) August 9, 2018 Updated – More details of death and destruction emerge from Lombok after the #IndonesiaEarthQuake . This graphic explains the tragedy https://t.co/MDscEPWc3A — Reuters Graphics (@ReutersGraphics) August 7, 2018 Liquifaksi (luquefaction) yaitu tanah yang kaku berubah menjadi gembur dan muncul lumpur akibat tekanan gempa 7 SR terjadi di Desa Selengen Kecamatan Kayangan Lombok Utara. Liquifaksi banyak menyebabkan bangunan roboh karena bangunan berdiri diatas tanah gembur dan pondasi patah. pic.twitter.com/Wfu1NhSkJW — Sutopo Purwo Nugroho (@Sutopo_PN) August 9, 2018
Earlier today there was a shallow M 6.4 earthquake with an epicenter on the island of Lombok, Indonesia. With a hypocentral depth of about 7.5 km, this size of an earthquake can be quite damaging. The USGS PAGER estimate of impact suggests that there is about a 10% chance that there are more than 10 fatalities. Hopefully there are none. There have been several aftershocks, two M > 5. I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.0.
Tectonic and geographic map of the eastern Sunda arc and vicinity. Active volcanoes are represented by triangles, and bathymetric contours are in kilometers. Thrust faults are shown with teeth on the upper plate. The dashed box encloses the study area.
Cartoon cross section of Timor today, (cf. Richardson & Blundell 1996, their BIRPS figs 3b, 4b & 7; and their fig. 6 gravity model 2 after Woodside et al. 1989; and Snyder et al. 1996 their fig. 6a). Dimensions of the filled 40 km deep present-day Timor Tectonic Collision Zone are based on BIRPS seismic, earthquake seismicity and gravity data all re-interpreted here from Richardson & Blundell (1996) and from Snyder et al. (1996). NB. The Bobonaro Melange, its broken formation and other facies are not indicated, but they are included with the Gondwana mega-sequence. Note defunct Banda Trench, now the Timor TCZ, filled with Australian continental crust and Asian nappes that occupy all space between Wetar Suture and the 2–3 km deep deformation front north of the axis of the Timor Trough. Note the much younger decollement D5 used exactly the same part of the Jurassic lithology of the Gondwana mega-sequence in the older D1 decollement that produced what appears to be much stronger deformation.
Comparison of hypocentral profiles across the (a) Java subduction zone and (b) Timor collision zone (paleo-Banda trench). Catalog compiled from multiple reporting agencies listed in Table 1. Events of Mw>4.0 are shown for period 1815 to 2015.
Location of SeaMARC II survey (Plate 1 and Figures 2) and geographic features discussed in text. Triangles on upper plates of thrust zones.
Bathymetry, faults, and mud diapirs of the central Flores thrust zone, based on interpretation of SeaMARC II data and seismic reflection profiles. Shown also are locations (circled numbers) of all seismic profiles. Mud diapirs are solid black. Triangles on upper plates of thrust faults.
Illustration of major tectonic elements in triple junction geometry: tectonic features labeled per Figure 1; seismicity from ISC-GEM catalog [Storchak et al., 2013]; faults in Savu basin from Rigg and Hall [2011] and Harris et al. [2009]. Purple line is edge of Australian continental basement and fore arc [Rigg and Hall, 2011]. Abbreviations: AR = Ashmore Reef; SR = Scott Reef; RS = Rowley Shoals; TCZ = Timor Collision Zone; ST = Savu thrust; SB = Savu Basin; TT = Timor thrust; WT =Wetar thrust; WASZ = Western Australia Shear Zone. Open arrows indicate relative direction of motion; solid arrows direction of vergence.
(a) Focal mechanism solutions for the study region. The focal mechanisms are classified based on depth intervals to illustrate the style of faulting within the different structural domains. Note (b) sinistral reverse motion along Timor trough, (c) subduction related pattern along Java trench, and dextral solutions along the western Australia extended margin (Figure 4a) north of 20°S. Centroid moment tensor (CMT) solutions [Dziewonski et al., 1981] are from the CMT project [Ekström et al., 2012; http://www.globalcmt.org/CMTcite.html] for events of Mw>5.0 for the period 1976 onward.
Topographic and tectonic map of the Indonesian archipelago and surrounding region. Labeled, shaded arrows show motion (NUVEL-1A model) of the first-named tectonic plate relative to the second. Solid arrows are velocity vectors derived from GPS surveys from 1991 through 2001, in ITRF2000. For clarity, only a few of the vectors for Sumatra are included. The detailed velocity field for Sumatra is shown in Figure 5. Velocity vector ellipses indicate 2-D 95% confidence levels based on the formal (white noise only) uncertainty estimates. NGT, New Guinea Trench; NST, North Sulawesi Trench; SF, Sumatran Fault; TAF, Tarera-Aiduna Fault. Bathymetry [Smith and Sandwell, 1997] in this and all subsequent figures contoured at 2 km intervals.
GPS velocities of Sunda and Banda arc region. Large black and grey arrow shows motion of Australia relative to Eurasia [DeMets et al., 1994]. Thin black arrows show GPS velocities of Sunda and Banda arc regions relative to Australia [Nugroho et al., 2009]. Seismicity from ISC-GEM catalog [Storchak et al., 2013]. Note reduction of station velocities from west to east indicating progressive coupling of the Banda arc to the Australian plate compared to the area along the Sunda arc.
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Map and cross-section of historical seismicity of the area around the deadly M6.4 earthquake on Lombok Island, Indonesia, that occurred a few days ago. The Flores Backarc Thrust has been suggested as a possible causative fault. pic.twitter.com/sxxLMT4Kep — Jascha Polet (@CPPGeophysics) July 30, 2018 The latest update about our response in #Lombok earthquake (29/7/2018) #PMISiapBantu pic.twitter.com/apZyv9dSH7 — Indonesian Red Cross (@palangmerah) July 29, 2018 #UPDATE Death toll rises to 13, with hundreds injured, after a powerful M6.4 #earthquake struck popular tourist island of #Lombok in Indonesia early morning — Bali Promotion Center💅 (@translatorbali) July 29, 2018 A 6.4 magnitude earthquake had hit Lombok and Sumbawa Islands today, killing at least 10, including a Malaysian. Here is a footage from Mt Rinjani. Our thoughts and prayers are with them. pic.twitter.com/hZ2zc4tV70 — | outdoorian (@twt_outdoor) July 29, 2018 BBC News – Indonesia earthquake: 10 dead on tourist island Lombok https://t.co/mC1ytJrsfV — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) July 29, 2018 Deadly #earthquake in #Lombok, #Indonesia – Link to our in-depth article – https://t.co/Dex2gm12Wh pic.twitter.com/KgiqYvUHSO — Armand Vervaeck 🎗️ (@ArmandVervaeck) July 29, 2018 Surveying the damage in Lombok after a powerful earthquake hit the popular tourist destination in Indonesiahttps://t.co/WIi1D8YuK5 pic.twitter.com/myRoTCMguy — BBC News (World) (@BBCWorld) July 29, 2018 Mw=6.5, SUMBAWA REGION, INDONESIA (Depth: 14 km), 2018/07/28 22:47:37 UTC – Full details here: https://t.co/3sCPDO5xqv pic.twitter.com/3yeO7KZrnk — Earthquakes (@geoscope_ipgp) July 28, 2018 Korban gempa Sembalun Lombok Timur pic.twitter.com/wdug832T8M — #2019GantiPresiden (@IpungLombok) July 28, 2018 Beberapa kondisi bangunan setelah Gempa di Lombok. Semoga tidak ada korban jiwa 🙏🏻 pic.twitter.com/kz4E9gm98O — baiq tanisya ellya m (@tanisyaEM) July 28, 2018 🇮🇩💢#Indonesia #Earthquake Mw 6.4 depth 10 km Lombok Región. — 🌎 (@Geo__Data) July 28, 2018 Estimated population in the felt area: 3.7 millions inhabitants pic.twitter.com/GcP4108N8u — EMSC (@LastQuake) July 28, 2018 strong #earthquake on #Lombok, #Indonesia, well felt on #Bali, #Sumbawa, damage expected pic.twitter.com/8yft7KEZmN — CATnews (@CATnewsDE) July 28, 2018 Wake up in the morning with the shaking bed ! Got called from farm and so many facility broke down..#agendafreetv #lombok #earthquake pic.twitter.com/GbANUMLpxW — Reyn (@suharja_reynard) July 28, 2018 #Earthquake_alert – The impact of 7/29/18 – 06:47 local time Mag 6.4 SR quake at 28 km NW of East Lombok w/ 10 km hypocenter, some structures & houses are damaged in Sambelia, East Lombok. The BPBD is still collecting the data. Source: @Sutopo_PN #Lombok pic.twitter.com/EewC7iPDQ4 https://t.co/bH7VHxVjFL — Desianto F. Wibisono (@TDesiantoFW) July 29, 2018 #UPDATE Death toll rises to 10, with 40 injured, after a powerful M6.4 #earthquake struck popular tourist island of #Lombok in Indonesia early morning pic.twitter.com/gpojRbC5iI — CGTN (@CGTNOfficial) July 29, 2018 At least 3 killed after powerful 6.4-magnitude earthquake strikes off Indonesian island of #Lombok https://t.co/rgma2EEZe9 pic.twitter.com/3sOESVHmjM — The Straits Times (@STcom) July 29, 2018 Sorry to say that reports of casualties are starting to filter through from the 6.4 magnitude #Lombok #Earthquake this morning, updates to come #LombokEarthquake https://t.co/w93y8aIOvj — Alison Bevege (@AlisonBevege) July 29, 2018 Thinking of many friends in #Lombok … never a dull moment https://t.co/8eaPNQljQr — Krista Slade (@krista_slade) July 29, 2018 #Update Indonesia's disaster response agency spokesman says 10 were dead, 40 injured after a M6.4 earthquake struck popular tourist island of #Lombok in Indonesia early morning. pic.twitter.com/CTjub5UG7A — China Daily (@ChinaDailyUSA) July 29, 2018 Powerful #Earthquake hits #Indonesia's #Lombok, 10 killed, houses damagedhttps://t.co/6ae6C4mNuB — https://t.co/qIz2A1IP5X pic.twitter.com/fwgcXfjeBX — Z9 (@Z9Network) July 29, 2018
Earthquake Report: Halmahera, Indonesia
I was just about done with these new maps and getting ready to start writing them up in an updated earthquake report when I noticed that there was an interesting earthquake, with few historic analogues, along the Western Australia Shear Zone offshore of northwestern Australia. I probably won’t get to that earthquake, but I started downloading some material and reviewing my literature for the region. I considered doing both of these tasks on Sunday (today). That was not to be as I awakened to an email about this magnitude M 7.3 earthquake in Halmahera, Indonesia. I have several earthquake reports for the Molucca Strait, west of Halmahera. So, I have some background literature and knowledge about this region already.
There was an earthquake along Molucca Strait that I could not work on due to my field work. So I will briefly mention that quake here. There was also a recent earthquake to the south, in the Banda Sea (here is my earthquake report for that event). The June earthquake had the same magnitude as today’s shaker, M = 7.3. However, the earlier quake was too deep to cause a tsunami (unlike today’s temblor). Earthquakes along the Molucca Strait have generated tsunami with wave heights of over 9 meters (30 feet) according toe Harris and Major, 2016.
https://earthquake.usgs.gov/earthquakes/eventpage/us70004jyv/executive
The Molucca Strait is a north-south oriented seaway formed by opposing subduction zone / thrust faults (convergent plate boundaries). See the “Geologic Fundamentals” section below for an explanation of different fault types. On the west of the Molucca Strait is a thrust fault that dips downwards to the west. On the east, there is a thrust fault that dips down to the east (beneath the island of Halmahera).
There is a major east-west trending (striking) strike-slip fault that comes into the region from the east, called the Sorong fault. There are multiple strands of this system. A splay of this Sorong fault splays northwards through the island of Halmahera. There may be additional details about how this splay relates to the Sorong fault, but I was unable to locate any references (or read the details) today. According to BMKG, the fault that is associated with this earthquake is the Sorong-Bacan fault.
Today’s M 7.3 Halmahera earthquake is a strike-slip earthquake (the plates move side-by-side, like the San Andreas or North Anatolia faults). Often people don’t think of tsunami when a strike-slip earthquake happens because there is often little vertical ground motion. Many people are otherwise familiar with thrust or subduction zone earthquakes, which can produce significant uplift and subsidence (vertical land motion), that can lead to significant tsunami.
However, there is abundant evidence that strike-slip earthquakes do cause tsunami, though often of much smaller size than their thrust/subduction siblings. The main difference is that these strike-slip generated tsunami are much smaller in size.
For example, the 1999 Izmit and 2012 Wharton Basin earthquakes provided empirical evidence of strike-slip earthquake triggered tsunami. More recently, the 28 September 2018 magnitude M 7.5 Dongalla-Palu earthquake caused a tsunami in Palu Bay, Sulawesi, Indonesia that exceeded 10 meters (33 feet) in wave height (wave run up elevation)!!! I just got an email from Dr. Lori Dengler who is an a conference where people claim that the earthquake is possibly singlehandedly responsible for this large wave. Previously people thought that there may have been submarine landslides that contributed to the size.
Here is the tide gage record from a gage near today’s M 7.3 earthquake. The earthquake epicenter appears to be on land, so the tsunami is possibly smaller because of this. Indonesia operates a network of tide gages throughout the region here. The gage data below are from the island of Gebe, about 50 miles to the east of the M 7.3 epicenter.
Here is a quote from the Meteorology, Climatology and Geophysics Agency (BMKG) website:
Based on community reports, it was shown that shocks were felt in Bitung and Manado with the intensity of IV-V MMI (felt by almost all residents, many people built), and in Ternate III-IV MMI (felt by many people in the house). Until now there have been no reports of damage due to a strong earthquake shock in northern Maluku last night. The impact of the North Maluku earthquake only caused a tremendous panic among the people. In the city of Manado, some of the houses of the walls had cracks in the building walls of the building with very light categories.
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange). Due to the high rate of seismicity in this region, I do not have an historic seismicity poster for this event.
Magnetic Anomalies
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Shaking Intensity and Potential for Ground Failure
Landslide ground shaking can change the Factor of Safety in several ways that might increase the driving force or decrease the resisting force. Keefer (1984) studied a global data set of earthquake triggered landslides and found that larger earthquakes trigger larger and more numerous landslides across a larger area than do smaller earthquakes. Earthquakes can cause landslides because the seismic waves can cause the driving force to increase (the earthquake motions can “push” the land downwards), leading to a landslide. In addition, ground shaking can change the strength of these earth materials (a form of resisting force) with a process called liquefaction.
Sediment or soil strength is based upon the ability for sediment particles to push against each other without moving. This is a combination of friction and the forces exerted between these particles. This is loosely what we call the “angle of internal friction.” Liquefaction is a process by which pore pressure increases cause water to push out against the sediment particles so that they are no longer touching.
An analogy that some may be familiar with relates to a visit to the beach. When one is walking on the wet sand near the shoreline, the sand may hold the weight of our body generally pretty well. However, if we stop and vibrate our feet back and forth, this causes pore pressure to increase and we sink into the sand as the sand liquefies. Or, at least our feet sink into the sand.
Below is a diagram showing how an increase in pore pressure can push against the sediment particles so that they are not touching any more. This allows the particles to move around and this is why our feet sink in the sand in the analogy above. This is also what changes the strength of earth materials such that a landslide can be triggered.
Below is a diagram based upon a publication designed to educate the public about landslides and the processes that trigger them (USGS, 2004). Additional background information about landslide types can be found in Highland et al. (2008). There was a variety of landslide types that can be observed surrounding the earthquake region. So, this illustration can help people when they observing the landscape response to the earthquake whether they are using aerial imagery, photos in newspaper or website articles, or videos on social media. Will you be able to locate a landslide scarp or the toe of a landslide? This figure shows a rotational landslide, one where the land rotates along a curvilinear failure surface.
Here is a map with landslide probability on it (Jessee et al., 2017). Please head over to that report for more information about the USGS Ground Failure products (landslides and liquefaction). Basically, earthquakes shake the ground and this ground shaking can cause landslides. We can see that there is a low probability for landslides. However, we have already seen photographic evidence for landslides and the lower limit for earthquake triggered landslides is magnitude M 5.5 (from Keefer 1984)
Here is a map showing liquefaction susceptibility (Zhu et al., 2017).
Seismic Hazard and Seismic Risk
Tsunami Hazard
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
Philippines | Western Pacific
Earthquake Reports
Social Media
Run-up of ~1 m possible around epicenter @ShakingEarth pic.twitter.com/uUHBuf3QkY
References:
Return to the Earthquake Reports page.
Earthquake Report: Indonesia
https://earthquake.usgs.gov/earthquakes/eventpage/us600044zz/executive
This earthquake is in a region of strike-slip faulting (if in downgoing plate for example) or subduction thrusting, so I thought it may or may not produce a tsunami. There are also intermediate depth quakes here (deeper than subduction zone megathrust events), like this earthquake (which reduces the chance of a tsunami). While we often don’t think of strike-slip earthquakes as those that could cause a tsunami, they can trigger tsunami, albeit smaller in size than those from subduction zone earthquakes or locally for landslides. But, I checked tsunami.gov just in case (result = no tsunami locally nor regionally). I also took a look at the tide gages in the region here and here (result = no observations).
South of this earthquake is a convergent plate boundary, where the Australia plate dives northwards beneath a part of the Sunda plate (Eurasia) forming the Java and Timor trenches (subduction zones). Far to the west, on 2 June 1994 there was a subduction zone megathrust earthquake along the Java Trench. Earlier, on 19 August 1977 there was an M 8.3 earthquake, but it was not a subduction zone thrust event, but an extensional earthquake in the downgoing Australia plate (Given and Kanamori, 19080). Both 1977 and 1994 events are shown on one of the maps below. The 1977 earthquake was tsunamigenic, creating a wave observed on tide gages at Damier, Hampton, and Port Hedland in Australia (Gusman et al., 2009).
To the north of the subduction zone, there is a parallel fault system that dips in the opposite direction as the subduction zone. This is referred to as a backthrust fault (it is a thrust fault and “backwards” to the main fault). The Wetar and Flores faults are both part of this backthrust system. In JUly and August of 2018 there was a series of earthquakes near the Island of Flores associated with this backthrust. Here is my final of 3 reports on those earthquakes.
The Timor trough wraps around to the north on its eastern end and eventually forms the Seram Trench, which dips to the south. The shape of these linked trenches forms a “U” shape with the open part of the U pointing to the west. Recently it has been published that the basin formed by these fault systems is the deepest forearc basin on Earth (Pownall et al., 2016). There was a subduction zone earthquake in 1938, called the Great Banda Sea Earthquake. Okal and Reymond (2003) prepared an earthquake mechanism for this M 8.5 earthquake.
To complicate matters, there is a large strike-slip system that comes into the area from the east (Papua New Guinea) and bisects the crest of the “U” shape. This strike slip system feeds into the backthrust so that the backthrust is both a thrust fault and a strike-slip fault. There are probably separate faults that accommodate these different senses of motion. There have been a series of strike-slip earthquakes in the 20th century associated with the strike-slip motion along this boundary. For example, Osada and Abe (1981) uses seismologic records (e.g. from seismometers) to prepare an earthquake mechanism for this M 8.1 earthquake. They found that it was an oblique strike-slip earthquake. The depth was pretty shallow compared to the M 7.3 earthquake I am reporting about today.
On 17 June 1987 there was another relatively shallow M 7.1 strike-slip earthquake on this strike-slip fault system.
However, there is also a deeper strike-slip fault within the Australia plate. This fault is probably what ruptured on 2 March 2005 (M 7.1) and 10 December 2012 (M 7.1). The M 7.3 earthquake from a day ago had a similar magnitude, depth, mechanism, and location as these earlier quakes. These may have all ruptured the same fault (or not).Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes. Some earthquakes have older focal mechanisms plotted in black and white.
Magnetic Anomalies
Global Strain
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
Indonesia | Sumatra
General Overview
Earthquake Reports
Social Media
References:
Return to the Earthquake Reports page.
Earthquake Report: Sulawesi, Indonesia
https://earthquake.usgs.gov/earthquakes/eventpage/us700034xq/executive
Just like the September quake, today’s event was a strike-slip earthquake, where the crust moves side-by-side (like the San Andreas fault).
This region of the world is complicated and special. There are subduction zone and transform plate boundaries. I use several maps below to present how these plate boundaries control the types of earthquakes. First I plot the earthquakes from the past year, then for the past century. Of course, let’s remember that seismometers are not that old, so the first half of the 20th century, there were not many seismometers. So, the earthquake record before the 1950s is generally composed of earthquakes with larger magnitude.
There are many many faults in this region, overlapping each other, offsetting each other. And, there have been earthquakes along many of these systems over the past year and past century that represent these different systems and how they interact.
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
Magnetic Anomalies
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Some Relevant Discussion and Figures
seismic tomography on coincident profile P31 (modified after Lüschen et al, 2011).
Geologic Fundamentals
Compressional:
Extensional:
Indonesia | Sumatra
General Overview
Earthquake Reports
Social Media
References:
Return to the Earthquake Reports page.
Earthquake Report: 2018 Summary
However, our historic record is very short, so any thoughts about whether this year (or last, or next) has smaller (or larger) magnitude earthquakes than “normal” are limited by this small data set.
Here is a table of the earthquakes M ≥ 6.5.
Here is a plot showing the cumulative release of seismic energy. This summary is imperfect in several ways, but shows how only the largest earthquakes have a significant impact on the tally of energy release from earthquakes. I only include earthquakes M ≥ 6.5. Note how the M 7.5 Sulawesi earthquake and how little energy was released relative to the two M = 7.9 earthquakes.
Below is my summary poster for this earthquake year
This is a video that shuffles through the earthquake report posters of the year
2018 Earthquake Report Pages
Other Annual Summaries
2018 Earthquake Reports
General Overview of how to interact with these summaries
Background on the Earthquake Report posters
Magnetic Anomalies
2018.01.10 M 7.6 Cayman Trough
Based upon our knowledge of the plate tectonics of this region, I can interpret the fault plane solution for this earthquake. The M 7.6 earthquake was most likely a left-lateral strike-slip earthquake associated with the Swan fault.
2018.01.14 M 7.1 Peru
In the region of this M 7.1 earthquake, two large structures in the NP are the Nazca Ridge and the Nazca fracture zone. The Nazca fracture zone is a (probably inactive) strike-slip fault system. The Nazca Ridge is an over-thickened region of the NP, thickened as the NP moved over a hotspot located near Salas y Gomez in the Pacific Ocean east of Easter Island (Ray et al., 2012).
There are many papers that discuss how the ridge affects the shape of the megathrust fault here. The main take-away is that the NR is bull dozing into South America and the dip of the subduction zone is flat here. There is a figure below that shows the deviation of the subducting slab contours at the NR.
Well, I missed looking further into a key update paper and used figures from an older paper on my interpretive poster yesterday. Thanks to Stéphane Baize for pointing this out! Turns out, after their new analyses, the M 7.1 earthquake was in a region of higher seismogenic coupling, rather than low coupling (as was presented in my first poster).
Also, Dr. Robin Lacassin noticed (as did I) the paucity of aftershocks from yesterday’s M 7.1. This was also the case for the carbon copy 2013 M 7.1 earthquake (there was 1 M 4.6 aftershock in the weeks following the M 7.1 earthquake on 2013.09.25; there were a dozen M 1-2 earthquakes in Nov. and Dec. of 2013, but I am not sure how related they are to the M 7.1 then). I present a poster below with this in mind. I also include below a comparison of the MMI modeled estimates. The 2013 seems to have possibly generated more widespread intensities, even though that was a deeper earthquake.
2018.01.23 M 7.9 Gulf of Alaska
This is strange because the USGS fault plane is oriented east-west, leading us to interpret the fault plane solution (moment tensor or focal mechanism) as a left-lateral strike-slip earthquake. So, maybe this earthquake is a little more complicated than first presumed. The USGS fault model is constrained by seismic waves, so this is probably the correct fault (east-west).
I prepared an Earthquake Report for the 1964 Good Friday Earthquake here.
So, that being said, here is the animation I put together. I used the USGS query tool to get earthquakes from 1/22 until now, M ≥ 1.5. I include a couple inset maps presented in my interpretive posters. The music is copyright free. The animations run through twice.
Here is a screenshot of the 14 MB video embedded below. I encourage you to view it in full screen mode (or download it).
2018.02.16 M 7.2 Oaxaca, Mexico
The SSN has a reported depth of 12 km, further supporting evidence that this earthquake was in the North America plate.
This region of the subduction zone dips at a very shallow angle (flat and almost horizontal).
There was also a sequence of earthquakes offshore of Guatemala in June, which could possibly be related to the M 8.1 earthquake. Here is my earthquake report for the Guatemala earthquake.
The poster also shows the seismicity associated with the M 7.6 earthquake along the Swan fault (southern boundary of the Cayman trough). Here is my earthquake report for the Guatemala earthquake.
2018.02.25 M 7.5 Papua New Guinea
This M 7.5 earthquake (USGS website) occurred along the Papua Fold and Thrust Belt (PFTB), a (mostly) south vergent sequence of imbricate thrust faults and associated fold (anticlines). The history of this PFTB appears to be related to the collision of the Australia plate with the Caroline and Pacific plates, the delamination of the downgoing oceanic crust, and then associated magmatic effects (from decompression melting where the overriding slab (crust) was exposed to the mantle following the delamination). More about this can be found in Cloos et al. (2005).
The aftershocks are still coming in! We can use these aftershocks to define where the fault may have slipped during this M 7.5 earthquake. As I mentioned yesterday in the original report, it turns out the fault dimension matches pretty well with empirical relations between fault length and magnitude from Wells and Coppersmith (1994).
The mapped faults in the region, as well as interpreted seismic lines, show an imbricate fold and thrust belt that dominates the geomorphology here (as well as some volcanoes, which are probably related to the slab gap produced by crust delamination; see Cloos et al., 2005 for more on this). I found a fault data set and include this in the aftershock update interpretive poster (from the Coordinating Committee for Geoscience Programmes in East and Southeast Asia, CCOP).
I initially thought that this M 7.5 earthquake was on a fault in the Papuan Fold and Thrust Belt (PFTB). Mark Allen pointed out on twitter that the ~35km hypocentral depth is probably too deep to be on one of these “thin skinned” faults (see Social Media below). Abers and McCaffrey (1988) used focal mechanism data to hypothesize that there are deeper crustal faults that are also capable of generating the earthquakes in this region. So, I now align myself with this hypothesis (that the M 7.5 slipped on a crustal fault, beneath the thin skin deformation associated with the PFTB. (thanks Mark! I had downloaded the Abers paper but had not digested it fully.
2018.03.08 M 6.8 New Ireland
The main transform fault (Weitin fault) is ~40 km to the west of the USGS epicenter. There was a very similar earthquake on 1982.08.12 (USGS website).
This earthquake is unrelated to the sequence occurring on the island of New Guinea.
Something that I rediscovered is that there were two M 8 earthquakes in 1971 in this region. This testifies that it is possible to have a Great earthquake (M ≥ 8) close in space and time relative to another Great earthquake. These earthquakes do not have USGS fault plane solutions, but I suspect that these are subduction zone earthquakes (based upon their depth).
This transform system is capable of producing Great earthquakes too, as evidenced by the 2000.11.16 M 8.0 earthquake (USGS website). This is another example of two Great earthquakes (or almost 2 Great earthquakes, as the M 7.8 is not quite a Great earthquake) are related. It appears that the M 8.0 earthquake may have triggered teh M 7.8 earthquake about 3 months later (however at first glance, it seemed to me like the strike-slip earthquake might not increase the static coulomb stress on the subduction zone, but I have not spent more than half a minute thinking about this).Main Interpretive Poster with emag2
Earthquakes M≥ 6.5 with emag2
2018.03.26 M 6.6 New Britain
Today’s M 6.6 earthquake happened close in proximity to a M 6.3 from 2 days ago and a M 5.6 from a couple weeks ago. The M 5.6 may be related (may have triggered these other earthquakes), but this region is so active, it might be difficult to distinguish the effects from different earthquakes. The M 5.6 is much deeper and looks like it was in the downgoing Solomon Sea plate. It is much more likely that the M 6.3 and M 6.6 are related (I interpret that the M 6.3 probably triggered the M 6.6, or that M 6.3 was a foreshock to the M 6.6, given they are close in depth). Both M 6.3 and M 6.6 are at depths close to the depth of the subducting slab (the megathrust fault depth) at this location. So, I interpret these to be subduction zone earthquakes.
2018.03.26 M 6.9 New Britain
2018.04.02 M 6.8 Bolivia
We are still unsure what causes an earthquake at such great a depth. The majority of earthquakes happen at shallower depths, caused largely by the frictional between differently moving plates or crustal blocks (where earth materials like the crust behave with brittle behavior and not elastic behavior). Some of these shallow earthquakes are also due to internal deformation within plates or crustal blocks.
As plates dive into the Earth at subduction zones, they undergo a variety of changes (temperature, pressure, stress). However, because people cannot directly observe what is happening at these depths, we must rely on inferences, laboratory analogs, and other indirect methods to estimate what is going on.
So, we don’t really know what causes earthquakes at the depth of this Bolivia M 6.8 earthquake. Below is a review of possible explanations as provided by Thorne Lay (UC Santa Cruz) in an interview in response to the 2013 M 8.3 Okhotsk Earthquake.
2018.05.04 M 6.9 Hawai’i
Hawaii is an active volcanic island formed by hotspot volcanism. The Hawaii-Emperor Seamount Chain is a series of active and inactive volcanoes formed by this process and are in a line because the Pacific plate has been moving over the hotspot for many millions of years.
Southeast of the main Kilauea vent, the Pu‘u ‘Ö‘ö crater saw an elevation of lava into the crater, leading to overtopping of the crater (on 4/30/2018). Seismicity migrated eastward along the ERZ. This morning, there was a M 5.0 earthquake in the region of the Hilina fault zone (HFZ). I was getting ready to write something up, but I had other work that I needed to complete. Then, this evening, there was a M 6.9 earthquake between the ERZ and the HFZ.
There have been earthquakes this large in this region in the past (e.g. the 1975.1.29 M 7.1 earthquake along the HFZ). This earthquake was also most likely related to magma injection (Ando, 1979). The 1975 M 7.1 earthquake generated a small tsunami (Ando, 1979). These earthquakes are generally compressional in nature (including the earthquakes from today).
Today’s earthquake also generated a tsunami as recorded on tide gages throughout Hawaii. There is probably no chance that a tsunami will travel across the Pacific to have a significant impact elsewhere.
Temblor Reports:
2018.05.05 Pele, the Hawai’i Goddess of Fire, Lightning, Wind, and Volcanoes
2018.05.06 Pele, la Diosa Hawaiana del Fuego, los Relámpagos, el Viento y los Volcanes de Hawái
2018.08.05 M 6.9 Lombok, Indonesia
However, it is interesting because the earthquake sequence from last week (with a largest earthquake with a magnitude of M 6.4) were all foreshocks to this M 6.9. Now, technically, these were not really foreshocks. The M 6.4 has an hypocentral (3-D location) depth of ~6 km and the M 6.9 has an hypocentral depth of ~31 km. These earthquakes are not on the same fault, so I would interpret that the M 6.9 was triggered by the sequence from last week due to static coulomb changes in stress on the fault that ruptured. Given the large difference in depths, the uncertainty for these depths is probably not sufficient to state that they may be on the same fault (i.e. these depths are sufficiently different that this difference is larger than the uncertainty of their locations).
I present a more comprehensive analysis of the tectonics of this region in my earthquake report for the M 6.4 earthquake here. I especially address the historic seismicity of the region there. This M 6.9 may have been on the Flores thrust system, while the earthquakes from last week were on the imbricate thrust faults overlying the Flores Thrust. See the map from Silver et al. (1986) below. I include the same maps as in my original report, but after those, I include the figures from Koulani et al. (2016) (the paper is available on researchgate).
2018.08.15 M 6.6 Aleutians
The Andreanof Islands is one of the most active parts of the Aleutian Arc. There have been many historic earthquakes here, some of which have been tsunamigenic (in fact, the email that notified me of this earthquake was from the ITIC Tsunami Bulletin Board).
Possibly the most significant earthquake was the 1957 Andreanof Islands M 8.6 Great (M ≥ 8.0) earthquake, though the 1986 M 8.0 Great earthquake is also quite significant. As was the 1996 M 7.9 and 2003 M 7.8 earthquakes. Lest we forget smaller earthquakes, like the 2007 M 7.2. So many earthquakes, so little time.
2018.08.18 M 8.2 Fiji
This earthquake is one of the largest earthquakes recorded historically in this region. I include the other Large and Great Earthquakes in the posters below for some comparisons.
Today’s earthquake has a Moment Magnitude of M = 8.2. The depth is over 550 km, so is very very deep. This region has an historic record of having deep earthquakes here. Here is the USGS website for this M 8.2 earthquake. While I was writing this, there was an M 6.8 deep earthquake to the northeast of the M 8.2. The M 6.8 is much shallower (about 420 km deep) and also a compressional earthquake, in contrast to the extensional M 8.2.
This M 8.2 earthquake occurred along the Tonga subduction zone, which is a convergent plate boundary where the Pacific plate on the east subducts to the west, beneath the Australia plate. This subduction zone forms the Tonga trench.
2018.08.19 M 6.9 Lombok, Indonesia
Today there was an M 6.3 soon followed by an M 6.9 earthquake (and a couple M 5.X quakes).
These earthquakes have been occurring along a thrust fault system along the northern portion of Lombok, Indonesia, an island in the magamatic arc related to the Sunda subduction zone. The Flores thrust fault is a backthrust to the subduction zone. The tectonics are complicated in this region of the world and there are lots of varying views on the tectonic history. However, there has been several decades of work on the Flores thrust (e.g. Silver et al., 1986). The Flores thrust is an east-west striking (oriented) north vergent (dipping to the south) thrust fault that extends from eastern Java towards the Islands of Flores and Timor. Above the main thrust fault are a series of imbricate (overlapping) thrust faults. These imbricate thrust faults are shallower in depth than the main Flores thrust.
The earthquakes that have been happening appear to be on these shallower thrust faults, but there is a possibility that they are activating the Flores thrust itself. Perhaps further research will illuminate the relations between these shallower faults and the main player, the Flores thrust.
2018.08.21 M 7.3 Venezuela
The northeastern part of Venezuela lies a large strike-slip plate boundary fault, the El Pilar fault. This fault is rather complicated as it strikes through the region. There are thrust faults and normal faults forming ocean basins and mountains along strike.
Many of the earthquakes along this fault system are strike-slip earthquakes (e.g. the 1997.07.09 M 7.0 earthquake which is just to the southwest of today’s temblor. However, today’s earthquake broke my immediate expectations for strike-slip tectonics. There is a south vergent (dipping to the north) thrust fault system that strikes (is oriented) east-west along the Península de Paria, just north of highway 9, east of Carupano, Venezuela. Audenard et al. (2000, 2006) compiled a Quaternary Fault database for Venezuela, which helps us interpret today’s earthquake. I suspect that this earthquake occurred on this thrust fault system. I bet those that work in this area even know the name of this fault. However, looking at the epicenter and the location of the thrust fault, this is probably not on this thrust fault. When I initially wrote this report, the depth was much shallower. Currently, the hypocentral (3-D location) depth is 123 km, so cannot be on that thrust fault.
The best alternative might be the subduction zone associated with the Lesser Antilles.
2018.08.24 M 7.1 Peru
While doing my lit review, I found the Okal and Bina (1994) paper where they use various methods to determine focal mechanisms for the some deep earthquakes in northern Peru. More about focal mechanisms below. These authors created focal mechanisms for the 1921 and 1922 deep earthquakes so they could lean more about the 1970 deep earthquake. Their seminal work here forms an important record of deep earthquakes globally. These three earthquakes are all extensional earthquakes, similar to the other deep earthquakes in this region. I label the 1921 and 1922 earthquakes a couplet on the poster.
There was also a pair of earthquakes that happened in November, 2015. These two earthquakes happened about 5 minutes apart. They have many similar characteristics, suggest that they slipped similar faults, if not the same fault. I label these as doublets also.
So, there may be a doublet companion to today’s M 7.1 earthquake. However, there may be not. There are examples of both (single and doublet) and it might not really matter for 99.99% of the people on Earth since the seismic hazard from these deep earthquakes is very low.
Other examples of doublets include the 2006 | 2007 Kuril Doublets (Ammon et al., 2008) and the 2011 Kermadec Doublets (Todd and Lay, 2013).
2018.09.05 M 6.6 Hokkaido, Japan
This earthquake is in an interesting location. to the east of Hokkaido, there is a subduction zone trench formed by the subduction of the Pacific plate beneath the Okhotsk plate (on the north) and the Eurasia plate (to the south). This trench is called the Kuril Trench offshore and north of Hokkaido and the Japan Trench offshore of Honshu.
One of the interesting things about this region is that there is a collision zone (a convergent plate boundary where two continental plates are colliding) that exists along the southern part of the island of Hokkaido. The Hidaka collision zone is oriented (strikes) in a northwest orientation as a result of northeast-southwest compression. Some suggest that this collision zone is no longer very active, however, there are an abundance of active crustal faults that are spatially coincident with the collision zone.
Today’s M 6.6 earthquake is a thrust or reverse earthquake that responded to northeast-southwest compression, just like the Hidaka collision zone. However, the hypocentral (3-D) depth was about 33 km. This would place this earthquake deeper than what most of the active crustal faults might reach. The depth is also much shallower than where we think that the subduction zone megathrust fault is located at this location (the fault formed between the Pacific and the Okhotsk or Eurasia plates). Based upon the USGS Slab 1.0 model (Hayes et al., 2012), the slab (roughly the top of the Pacific plate) is between 80 and 100 km. So, the depth is too shallow for this hypothesis (Kuril Trench earthquake) and the orientation seems incorrect. Subduction zone earthquakes along the trench are oriented from northwest-southweast compression, a different orientation than today’s M 6.6.
So today’s M 6.6 earthquake appears to have been on a fault deeper than the crustal faults, possibly along a deep fault associated with the collision zone. Though I am not really certain. This region is complicated (e.g. Kita et al., 2010), but there are some interpretations of the crust at this depth range (Iwasaki et al., 2004) shown in an interpreted cross section below.
Temblor Reports:
2018.09.06 Violent shaking triggers massive landslides in Sapporo Japan earthquake
2018.09.09 M 6.9 Kermadec
This earthquake was quite deep, so was not expected to generate a significant tsunami (if one at all).
There are several analogies to today’s earthquake. There was a M 7.4 earthquake in a similar location, but much deeper. These are an interesting comparison because the M 7.4 was compressional and the M 6.9 was extensional. There is some debate about what causes ultra deep earthquakes. The earthquakes that are deeper than about 40-50 km are not along subduction zone faults, but within the downgoing plate. This M 6.9 appears to be in a part of the plate that is bending (based on the Benz et al., 2011 cross section). As plates bend downwards, the upper part of the plate gets extended and the lower part of the plate experiences compression.
2018.09.28 M 7.5 Sulawesi
This area of Indonesia is dominated by a left-lateral (sinistral) strike-slip plate boundary fault system. Sulawesi is bisected by the Palu-Kola / Matano fault system. These faults appear to be an extension of the Sorong fault, the sinistral strike-slip fault that cuts across the northern part of New Guinea.
There have been a few earthquakes along the Palu-Kola fault system that help inform us about the sense of motion across this fault, but most have maximum magnitudes mid M 6.
GPS and block modeling data suggest that the fault in this area has a slip rate of about 40 mm/yr (Socquet et al., 2006). However, analysis of offset stream channels provides evidence of a lower slip rate for the Holocene (last 12,000 years), a rate of about 35 mm/yr (Bellier et al., 2001). Given the short time period for GPS observations, the GPS rate may include postseismic motion earlier earthquakes, though these numbers are very close.
Using empirical relations for historic earthquakes compiled by Wells and Coppersmith (1994), Socquet et al. (2016) suggest that the Palu-Koro fault system could produce a magnitude M 7 earthquake once per century. However, studies of prehistoric earthquakes along this fault system suggest that, over the past 2000 years, this fault produces a magnitude M 7-8 earthquake every 700 years (Bellier et al., 2006). So, it appears that this is the characteristic earthquake we might expect along this fault.
Most commonly, we associate tsunamigenic earthquakes with subduction zones and thrust faults because these are the types of earthquakes most likely to deform the seafloor, causing the entire water column to be lifted up. Strike-slip earthquakes can generate tsunami if there is sufficient submarine topography that gets offset during the earthquake. Also, if a strike-slip earthquake triggers a landslide, this could cause a tsunami. We will need to wait until people take a deeper look into this before we can make any conclusions about the tsunami and what may have caused it.
My 2018.10.01 BC Newshour Interview
InSAR Analysis
Interferometric SAR (InSAR) utilizes two separate SAR data sets to determine if the ground surface has changed over time, the time between when these 2 data sets were collected. More about InSAR can be found here and here. Explaining the details about how these data are analyzed is beyond the scope of this report. I rely heavily on the expertise of those who do this type of analysis, for example Dr. Eric Fielding.
M 7.5 Landslide Model vs. Observation Comparison
Until these landslides are analyzed and compared with regions that did not fail in slope failure, we will not be able to reconstruct what happened… why some areas failed and some did not.
There are landslide slope stability and liquefaction susceptibility models based on empirical data from past earthquakes. The USGS has recently incorporated these types of analyses into their earthquake event pages. More about these USGS models can be found on this page.
I prepared some maps that compare the USGS landslide and liquefaction probability maps. Below I present these results along with the MMI contours. I also include the faults mapped by Wilkinson and Hall (2017). Shown are the cities of Donggala and Palu. Also shown are the 2 tide gage locations (Pantoloan Port – PP and Mumuju – M). I also used post-earthquake satellite imagery to outline the largest landslides in Palu Valley, ones that appear to be lateral spreads.
Temblor Reports:
2018.09.28 The Palu-Koro fault ruptures in a M=7.5 quake in Sulawesi, Indonesia, triggering a tsunami and likely more shocks
2018.10.03 Tsunami in Sulawesi, Indonesia, triggered by earthquake, landslide, or both
2018.10.16 Coseismic Landslides in Sulawesi, Indonesia
2018.10.10 M 7.0 New Britain, PNG
The subduction zone forms the New Britain Trench with an axis that trends east-northeast. To the east of New Britain, the subduction zone bends to the southeast to form the San Cristobal and South Solomon trenches. Between these two subduction zones is a series of oceanic spreading ridges sequentially offset by transform (strike slip) faults.
Earthquakes along the megathrust at the New Britain trench are oriented with the maximum compressive stress oriented north-northwest (perpendicular to the trench). Likewise, the subduction zone megathrust earthquakes along the S. Solomon trench compress in a northeasterly direction (perpendicular to that trench).
There is also a great strike slip earthquake that shows that the transform faults are active.
This earthquake was too small and too deep to generate a tsunami.
Temblor Reports:
2018.10.10 M 7.5 Earthquake in New Britain, Papua New Guinea
2018.10.22 M 6.8 Explorer plate
The Juan de Fuca plate is created at an oceanic spreading center called the Juan de Fuca Ridge. This spreading ridge is offset by several transform (strike-slip) faults. At the southern terminus of the JDF Ridge is the Blanco fault, a transtensional transform fault connecting the JDF and Gorda ridges.
At the northern terminus of the JDF Ridge is the Sovanco transform fault that strikes to the northwest of the JDF Ridge. There are additional fracture zones parallel and south of the Sovanco fault, called the Heck, Heckle, and Springfield fracture zones.
The first earthquake (M = 6.6) appears to have slipped along the Sovanco fault as a right-lateral strike-slip earthquake. Then the M 6.8 earthquake happened and, given the uncertainty of the location for this event, occurred on a fault sub-parallel to the Sovanco fault. Then the M 6.5 earthquake hit, back on the Sovanco fault.
2018.10.25 M 6.8 Greece
Both of those earthquakes were right-lateral strike-slip earthquakes associated with the Kefallonia fault.
However, today’s earthquake sequence was further to the south and east of the strike-slip fault, in a region experiencing compression from the Ionian Trench subduction zone. But there is some overlap of these different plate boundaries, so the M 6.8 mainshock is an oblique earthquake (compressional and strike-slip). Based upon the sequence, I interpret this earthquake to be right-lateral oblique. I could be wrong.
Temblor Reports:
2018.10.26 Greek earthquake in a region of high seismic hazard
2018.11.08 M 6.8 Mid Atlantic Ridge (Jan Mayen fracture zone)
North of Iceland, the MAR is offset by many small and several large transform faults. The largest transform fault north of Iceland is called the Jan Mayen fracture zone, which is the location for the 2018.11.08 M = 6.8 earthquake.
2018.11.30 M 7.0 Alaska
During the 1964 earthquake, the downgoing Pacific plate slipped past the North America plate, including slip on “splay faults” (like the Patton fault, no relation, heheh). There was deformation along the seafloor that caused a transoceanic tsunami.
The Pacific plate has pre-existing zones of weakness related to fracture zones and spreading ridges where the plate formed and are offset. There was an earthquake in January 2016 that may have reactivated one of these fracture zones. This earthquake (M = 7.1) was very deep (~130 km), but still caused widespread damage.
The earthquake appears to have a depth of ~40 km and the USGS model for the megathrust fault (slab 2.0) shows the megathrust to be shallower than this earthquake. There are generally 2 ways that may explain the extensional earthquake: slab tension (the downgoing plate is pulling down on the slab, causing extension) or “bending moment” extension (as the plate bends downward, the top of the plate stretches out.
Temblor Reports:
2018.11.30 Exotic M=7.0 earthquake strikes beneath Anchorage, Alaska
2018.12.11 What the Anchorage earthquake means for the Bay Area, Southern California, Seattle, and Salt Lake City
2018.12.05 M 7.5 New Caledonia
This part of the plate boundary is quite active and I have a number of earthquake reports from the past few years (see below, a list of earthquake reports for this region).
But the cool thing from a plate tectonics perspective is that there was a series of different types of earthquakes. At first view, it appears that there was a mainshock with a magnitude of M = 7.5. There was a preceding M 6.0 earthquake which may have been a foreshock.
The M 7.5 earthquake was an extensional earthquake. This may be due to either extension from slab pull or due to extension from bending of the plate. More on this later.
Following the M 7.5, there was an M 6.6 earthquake, however, this was a thrust or reverse (compressional) earthquake. The M 6.6 may have been in the upper plate or along the subduction zone megathrust fault, but we won’t know until the earthquake locations are better determined.
A similar sequence happened in October/November 2017. I prepared two reports for this sequence here and here. Albeit, in 2017, the thrust earthquake was first (2017.10.31 vs. 2017.11.19).
There have been some observations of tsunami. Below is from the Pacific Tsunami Warning Center.
2018.12.20 M 7.4 Bering Kresla
This earthquake happened in an interesting region of the world where there is a junction between two plate boundaries, the Kamchatka subduction zone with the Aleutian subduction zone / Bering-Kresla Shear Zone. The Kamchatka Trench (KT) is formed by the subduction (a convergent plate boundary) beneath the Okhotsk plate (part of North America). The Aleutian Trench (AT) and Bering-Kresla Shear Zone (BKSZ) are formed by the oblique subduction of the Pacific plate beneath the Pacific plate. There is a deflection in the Kamchatka subduction zone north of the BKSZ, where the subduction trench is offset to the west. Some papers suggest the subduction zone to the north is a fossil (inactive) plate boundary fault system. There are also several strike-slip faults subparallel to the BKSZ to the north of the BKSZ.
UPDATE #1
2018.12.29 M 7.0 Philippines
The earthquake was quite deep, which makes it less likely to cause damage to people and their belongings (e.g. houses and roads) and also less likely that the earthquake will trigger a trans-oceanic tsunami.
Here are the tidal data:
Geologic Fundamentals
Compressional:
Extensional:
Return to the Earthquake Reports page.
Earthquake/Landslide/Tsunami Report: Donggala Earthquake, Central Sulawesi: UPDATE #1
In short, there was an earthquake with magnitude M = 7.5 on 2018.09.28. Minutes after the earthquake there was a tsunami that hit the coasts of Palu Bay. Possibly during the earthquake, kilometer scale landslides were triggered along the floor of Palu Valley.
These three natural disasters would be devastating on their own, but when considered in their totality, this trifecta has led to considerable suffering in central Sulawesi, Indonesia.
M 7.5 Doggala Earthquake
Here is a map that shows the updated USGS model of ground shaking. The USGS prepared an updated earthquake fault slip model that was additionally informed by post-earthquake analysis of ground deformation. The original fault model extended from north of the epicenter to the northernmost extent of Palu City. Soon after the earthquake, Dr. Sotiris Valkaniotis prepared a map that showed large horizontal offsets across the ruptured fault along the entire length of the western margin on Palu Valley. This horizontal offset had an estimated ~8 meters of relative displacement. InSAR analyses confirmed that the coseismic ground deformation extended through Palu Valley and into the mountains to the south of the valley.
My 2018.10.01 BC Newshour Interview
Optical Analysis
Pixels are “picture elements” that comprise what a raster is created out of. Consider a television or computer monitor. The screen is displaying rows and columns of colored light. Each cell of this “raster” display is called a pixel.
Basically, the software compares the patterns in the compared imagery to detect changes. If a group of pixels in the image move relative to other pixels, then this motion is quantified. This type of analysis is particularly useful for strike-slip earthquakes as the ground moves side by side.
Dr. Valkniotis has used a variety of imagery types. Below are a couple products that they have shared on social media. Please contact Dr. Valkaniotis for more information!
InSAR Analysis
Interferometric SAR (InSAR) utilizes two separate SAR data sets to determine if the ground surface has changed over time, the time between when these 2 data sets were collected. More about InSAR can be found here and here. Explaining the details about how these data are analyzed is beyond the scope of this report. I rely heavily on the expertise of those who do this type of analysis, for example Dr. Eric Fielding.
Below are a series of different InSAR analytical results.
Tsunami
Tsunami can be caused by a variety of processes, including earthquakes, volcanic eruptions, landslides, and meteorological phenomena. Earthquakes, eruptions, and landslides cause tsunami when these processes displace water in some way. We may typically associate tsunami with subduction zone earthquakes because these earthquakes are the type that generate vertical land motion along the sea floor. However, we know that strike-slip earthquakes can also generate tsunami (e.g. the 1999 Izmit, Turkey earthquake). But strike-slip earthquakes typically generate tsunami that are smaller in size.
When landslides generate tsunami, they are often localized relative to the location of the landslide. The tsunami size can be rather large near the landslide and the size diminishes rapidly with distance from the landslide. An example of a landslide generated tsunami is the 1998 Papua New Guinea tsunami (an earthquake triggered a landslide, causing a “larger than expected” tsunami to inundate the land there. The size of the tsunami was very large near the landslide.
Based on post-earthquake satellite imagery from Digital Globe, the overwhelming majority of tsunami damage is localized within Palu Bay. The severity of damage is worse in southern Palu Bay where tsunami inundation is on the order of 300 feet. While at the northern part of the bay, inundation is on the order of 50 feet. In the north, most of the buildings that were destroyed by the tsunami were built over the water, though not entirely. While in the south, building damage extends further inland where buildings have been destroyed that were not built over the water. North of the mouth of the bay, there is less evidence for tsunami inundation, but there is localized damage in places.
There was a tsunami recorded at the Pantoloan Port tide gage with an amplitude of about 1 meter. At this location is also a 50 long ship that was lifted up onto a dock at the port. More details about the observations made by the joint Indonesia/Japan post-tsunami survey team cab be found at Temblor here.
M 7.5 Landslide Model vs. Observation Comparison
While remote sensing methods are useful to locate damage in the region, field observations will be key in the effort to analyze the landscape response to these natural disasters. The Indonesian government and international researchers are already surveying the region and collecting these important observational details.
There are many different ways in which a landslide can be triggered. The first order relations behind slope failure (landslides) is that the “resisting” forces that are preventing slope failure (e.g. the strength of the bedrock or soil) are overcome by the “driving” forces that are pushing this land downwards (e.g. gravity). The ratio of resisting forces to driving forces is called the Factor of Safety (FOS). We can write this ratio like this:
Landslide ground shaking can change the Factor of Safety in several ways that might increase the driving force or decrease the resisting force. Keefer (1984) studied a global data set of earthquake triggered landslides and found that larger earthquakes trigger larger and more numerous landslides across a larger area than do smaller earthquakes. Earthquakes can cause landslides because the seismic waves can cause the driving force to increase (the earthquake motions can “push” the land downwards), leading to a landslide. In addition, ground shaking can change the strength of these earth materials (a form of resisting force) with a process called liquefaction.
Sediment or soil strength is based upon the ability for sediment particles to push against each other without moving. This is a combination of friction and the forces exerted between these particles. This is loosely what we call the “angle of internal friction.” Liquefaction is a process by which pore pressure increases cause water to push out against the sediment particles so that they are no longer touching.
An analogy that some may be familiar with relates to a visit to the beach. When one is walking on the wet sand near the shoreline, the sand may hold the weight of our body generally pretty well. However, if we stop and vibrate our feet back and forth, this causes pore pressure to increase and we sink into the sand as the sand liquefies. Or, at least our feet sink into the sand.
Below is a diagram showing how an increase in pore pressure can push against the sediment particles so that they are not touching any more. This allows the particles to move around and this is why our feet sink in the sand in the analogy above. This is also what changes the strength of earth materials such that a landslide can be triggered.
Below is a diagram based upon a publication designed to educate the public about landslides and the processes that trigger them (USGS, 2004). Additional background information about landslide types can be found in Highland et al. (2008). There was a variety of landslide types that can be observed surrounding the earthquake region. So, this illustration can help people when they observing the landscape response to the earthquake whether they are using aerial imagery, photos in newspaper or website articles, or videos on social media. Will you be able to locate a landslide scarp or the toe of a landslide? This figure shows a rotational landslide, one where the land rotates along a curvilinear failure surface.
A lateral spread is a translational landslide that occurs over gentle slopes or flat terrain. The failure surface is more planar and less curvy than for rotational slides. The spread is usually caused when a confined layer of sediment is transformed from a solid into a liquid state. In the lateral spread figure below, it is the water that exists in the “silt and sand” deposits that has an increase in pore pressure to generate liquefaction, causing the failure. The overlying sediment is more cohesive, which is why we may have seen landslides move as coherent blocks across the landscape. However, these landslide blocks may disaggregate as they move, sometimes turning into a flow. This entire range of behavior can be seen in the post-earthquake aerial imagery of Palu Valley.
Here is an excellent educational video from IRIS and a variety of organizations. The video helps us learn about how earthquake intensity gets smaller with distance from an earthquake. The concept of liquefaction is reviewed and we learn how different types of bedrock and underlying earth materials can affect the severity of ground shaking in a given location. The intensity map above is based on a model that relates intensity with distance to the earthquake, but does not incorporate changes in material properties as the video below mentions is an important factor that can increase intensity in places.
If we look at the map at the top of this report, we might imagine that because the areas close to the fault shake more strongly, there may be more landslides in those areas. This is probably true at first order, but the variation in material properties and water content also control where landslides might occur.
There has been a large amount of videos posted online via social media and professional news organizations showing the impact of these landslides. Perhaps one of the best places to seek an expert informed view of landslide processes, of all types, is from Dr. David Petley and his blog, The Landslide Blog. Petley has presented a couple summaries of these observations of coseismic (during the earthquake) landslides as triggered by ground shaking from the M=7.5 Donggala earthquake.
The company Digital Globe provides high resolution satellite imagery for a fee, but they distribute imagery for free via their open data program following natural disasters. This imagery is available for noncommercial use including disaster impact analysis. Many of the preliminary analyses of impact presented on social media by subject matter experts has been based upon this imagery. Another source of fee based imagery is from Planet Lab that also provides imagery in support of peoples’ response to natural disasters via their disaster data program.
Most of the entire Palu Valley has previously been mapped as susceptible to liquefaction due to (1) the underlying materials are sediments and (2) a shallow ground water table (lots of water in the sediment, reaching close to the ground surface). The northern part of the valley is a river delta full of loose and water saturated sediments. Yet, only a small portion of the entire valley failed as these km scale lateral spreads.
Why is this? This is probably due to a combination of factors, but the biggest factor may be the heterogeneity of the underlying earth materials. These sediments probably have variation in material properties: strength (“angle of internal friction“), stickiness (“cohesion“), and porosity (spaces between sediment particles that can be filled with water).
Below is the liquefaction susceptibility map prepared in 2012. I just noticed that one of the 2 largest landslides actually happened outside of these liquefaction zones.
It is also possible that the earthquake intensity (ground shaking and seismic wave energy), that was directed in different directions, may have caused different amounts of “seismic loading” of these slopes.
Knowing how these material properties vary spatially is difficult to know as the materials in the subsurface are generally not in plain view (buried under ground). People can drill and sample the material properties (an engineering geologist) and then calculate the strength of these materials (engineer) on a site by site basis.
Until these landslides are analyzed and compared with regions that did not fail in slope failure, we will not be able to reconstruct what happened… why some areas failed and some did not.
There are landslide slope stability and liquefaction susceptibility models based on empirical data from past earthquakes. The USGS has recently incorporated these types of analyses into their earthquake event pages. More about these USGS models can be found on this page.
I prepared some maps that compare the USGS landslide and liquefaction probability maps. Below I present these results along with the MMI contours. I also include the faults mapped by Wilkinson and Hall (2017). Shown are the cities of Donggala and Palu. Also shown are the 2 tide gage locations (Pantoloan Port – PP and Mumuju – M). I also used post-earthquake satellite imagery to outline the largest landslides in Palu Valley, ones that appear to be lateral spreads.
References:
Earthquake Report: Sulawesi (Celebes), Indonesia
This area of Indonesia is dominated by a left-lateral (sinistral) strike-slip plate boundary fault system. Sulawesi is bisected by the Palu-Kola / Matano fault system. These faults appear to be an extension of the Sorong fault, the sinistral strike-slip fault that cuts across the northern part of New Guinea.
There have been a few earthquakes along the Palu-Kola fault system that help inform us about the sense of motion across this fault, but most have maximum magnitudes mid M 6.
GPS and block modeling data suggest that the fault in this area has a slip rate of about 40 mm/yr (Socquet et al., 2006). However, analysis of offset stream channels provides evidence of a lower slip rate for the Holocene (last 12,000 years), a rate of about 35 mm/yr (Bellier et al., 2001). Given the short time period for GPS observations, the GPS rate may include postseismic motion earlier earthquakes, though these numbers are very close.
Using empirical relations for historic earthquakes compiled by Wells and Coppersmith (1994), Socquet et al. (2016) suggest that the Palu-Koro fault system could produce a magnitude M 7 earthquake once per century. However, studies of prehistoric earthquakes along this fault system suggest that, over the past 2000 years, this fault produces a magnitude M 7-8 earthquake every 700 years (Bellier et al., 2006). So, it appears that this is the characteristic earthquake we might expect along this fault.
Based on what we know about strike-slip fault earthquakes, the portions of the fault to the north and south of today’s sequence may have an increased amount of stress due to this earthquake. Stay tuned for a Temblor.net report about this earthquake where I discuss this further.
There are reports of a local tsunami with a run-up about 2 meters. However, the UNESCO Sea Level Monitoring Facility (website) does not show any tsunami observations on tide gage data in the region.
Most commonly, we associate tsunamigenic earthquakes with subduction zones and thrust faults because these are the types of earthquakes most likely to deform the seafloor, causing the entire water column to be lifted up. Strike-slip earthquakes can generate tsunami if there is sufficient submarine topography that gets offset during the earthquake. Also, if a strike-slip earthquake triggers a landslide, this could cause a tsunami. We will need to wait until people take a deeper look into this before we can make any conclusions about the tsunami and what may have caused it.
Did you feel this earthquake? If so, fill out the USGS “Did You Feel It?” form here. If not, why not? Probably because you were too far away. The closer to an earthquake, the more strong the shaking intensity and the larger chance of infrastructure damage (roads, houses, etc.). The USGS PAGER alert for this earthquake shows that there are ~282,000 people living in Palu, a city near the epicenter. The estimate for shaking intensity is a MMI VI, which could result in light damage for resistant structures and moderate damage for vulnerable structures. More about USGS PAGER alerts here. There exists a possibility that there were more than 100 fatalities from this earthquake.UPDATE 2018.09.28 23:00
UPDATE 2018.09.29 07:00
I prepared a report for Temblor where we present results of static coulomb stress modeling. Here is that report.UPDATE 2018.09.29 10:45
UPDATE 2018.09.30 17:00
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
Magnetic Anomalies
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
Indonesia | Sumatra
General Overview
Earthquake Reports
Philippines | Western Pacific
Earthquake Reports
Social Media
After 7.7 SR earthquake strike Palu, then tsunami hit this city. #EarthQuake #Gempa #Tsunami #Palu #PrayForIndonesia #PrayForPalu #PrayForDonggala pic.twitter.com/G3JxTaUZx9
Earthquake just off Sulawesi island, #Indonesia. Triggering a powerful tsunami. Video captured by a local. #tsunami #breakingnews #Televisa Video del momento en el que llego el #Tsunamipic.twitter.com/bZgBUh2bGa
UPDATE 2018.09.29 07:00
References:
Earthquake Report Pages
Earthquake Report: Lombok, Indonesia
After a pretty seismically quiet first half of 2018, we have been catching up rapidly. The ultra deep Great Earthquake in Fiji. And now the Lombok sequence continues.
https://earthquake.usgs.gov/earthquakes/eventpage/us1000gda5/executive
The inhabitants and tourists in the Lombok, Indonesia region have been experiencing quite a few deadly and damaging earthquakes.
This ongoing sequence began in late July with a Mw 6.4 earthquake. Followed less than 2 weeks later with a Mw 6.9 earthquake.
Today there was an M 6.3 soon followed by an M 6.9 earthquake (and a couple M 5.X quakes).
These earthquakes have been occurring along a thrust fault system along the northern portion of Lombok, Indonesia, an island in the magamatic arc related to the Sunda subduction zone. The Flores thrust fault is a backthrust to the subduction zone. The tectonics are complicated in this region of the world and there are lots of varying views on the tectonic history. However, there has been several decades of work on the Flores thrust (e.g. Silver et al., 1986). The Flores thrust is an east-west striking (oriented) north vergent (dipping to the south) thrust fault that extends from eastern Java towards the Islands of Flores and Timor. Above the main thrust fault are a series of imbricate (overlapping) thrust faults. These imbricate thrust faults are shallower in depth than the main Flores thrust.
The earthquakes that have been happening appear to be on these shallower thrust faults, but there is a possibility that they are activating the Flores thrust itself. Perhaps further research will illuminate the relations between these shallower faults and the main player, the Flores thrust.
There are 2 main ways that earthquakes may be triggered by a previous earthquake.
I presented this on my earlier earthquake report, but this still holds true. People had been asking me if we might expect another large or larger earthquake in this region. So, here is what I have told them:
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes. The focal mechanism from the 1977.08.19 M 8.3 earthquake came from Lynnes and Lay, 1988.
Magnetic Anomalies
I include some inset figures.
Other Report Pages
Some Relevant Discussion and Figures
seismic tomography on coincident profile P31 (modified after Lüschen et al, 2011).
Black contours are 5 cm (2 inches). Copernicus Sentinel-1 data acquired on 30 July and 5 August 2018. White areas where measurement not possible, largely due to dense forests.
Measurements with #InSAR are in direction towards satellite, so not purely vertical or horizontal. Mostly vertical in this case.
My preliminary interpretation is that uplift is due to a north-dipping blind thrust fault that would project to the surface near the “zero” level of the interferogram, but a south-dipping thrust fault is also possible with down-dip end of rupture beneath the “zero” line
Geologic Fundamentals
Compressional:
Extensional:
Indonesia | Sumatra Earthquake Reports
General Overview
Earthquake Reports
Social Media
UPDATE 2018.08.21
UPDATE 2018.09.04
References:
°
≥Earthquake Report: Lombok, Indonesia: Update #1
However, it is interesting because the earthquake sequence from last week (with a largest earthquake with a magnitude of M 6.4) were all foreshocks to this M 6.9. Now, technically, these were not really foreshocks. The M 6.4 has an hypocentral (3-D location) depth of ~6 km and the M 6.9 has an hypocentral depth of ~31 km. These earthquakes are not on the same fault, so I would interpret that the M 6.9 was triggered by the sequence from last week due to static coulomb changes in stress on the fault that ruptured. Given the large difference in depths, the uncertainty for these depths is probably not sufficient to state that they may be on the same fault (i.e. these depths are sufficiently different that this difference is larger than the uncertainty of their locations).
I present a more comprehensive analysis of the tectonics of this region in my earthquake report for the M 6.4 earthquake here. I especially address the historic seismicity of the region there. This M 6.9 may have been on the Flores thrust system, while the earthquakes from last week were on the imbricate thrust faults overlying the Flores Thrust. See the map from Silver et al. (1986) below. I include the same maps as in my original report, but after those, I include the figures from Koulani et al. (2016) (the paper is available on researchgate).UPDATE 2018.08.08
Find out more about InSAR (Interferometric Synthetic Aperture Radar) here.
In addition, as Dr. Anthony Lomax pointed out, the USGS depth uncertainty is large enough for these earthquakes that they may be along the same fault.
Dr. Fielding uses the InSAR data (see update below) to interpret the fault geometry.UPDATE 2018.08.12
UPDATE 2018.08.19
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
Magnetic Anomalies
I include some inset figures.
Other Report Pages
Some Relevant Discussion and Figures
UPDATE 2018.08.08
NASA InSAR
Black contours are 5 cm (2 inches). Copernicus Sentinel-1 data acquired on 30 July and 5 August 2018. White areas where measurement not possible, largely due to dense forests.
Measurements with #InSAR are in direction towards satellite, so not purely vertical or horizontal. Mostly vertical in this case.
My preliminary interpretation is that uplift is due to a north-dipping blind thrust fault that would project to the surface near the “zero” level of the interferogram, but a south-dipping thrust fault is also possible with down-dip end of rupture beneath the “zero” line
Rusi P InSAR
Geologic Fundamentals
Compressional:
Extensional:
Indonesia | Sumatra Earthquake Reports
General Overview
Earthquake Reports
Social Media
Much scatter due to different earthquake types, but 50sec is on the high end for M7.https://t.co/po5va0kmlXhttps://t.co/y2FptSd3YU pic.twitter.com/fgg6EGeOPk
A: "Worldwide the probability that an earthquake will be followed within 3 days by a large earthquake nearby is somewhere just over 6%." – @USGS https://t.co/pgaXc03xsT
The earthquake was the main shock following its foreshocks, a nearby M 6.4 earthquake on the morning of 29 July 2018. 91 people confirmed killed ,over 100 confirmed injured. pic.twitter.com/2wFW8FrAgq
UPDATE 2018.08.08
NASA Disasters data portal https://t.co/v7V1sNFqq4
UPDATE 2018.08.09
References:
Earthquake Report: Lombok, Indonesia
This earthquake is probably along a thrust fault associated with the Flores thrust fault, a north vergent (dipping into the earth in a southerly direction) back thrust fault to the Sunda subduction zone fault. The Flores thrust possibly extends from east of Timor on the east to the northern shore of Java (McCaffrey and Nabelek, 1987). Others suggest that the Flores thrust ends at a cross fault just east of Lombok (Hengresh and Whitney, 2016). However, the seismic profiles from Silver et al. (1986) are convincing that there are east-west compressional structures extending between the northern shore of Java to where the Flores thrust is mapped.
Detailed mapping of the seafloor to the east of Lombok, north of the island of Sumbawa, reveals that there are imbricate (overlapping) thrust faults (Silver et al., 1986). I think that it is reasonable to presume that there are similar structures on the northern flank of Lombok.
Lombok is also a volcano complex as part of the Sunda magmatic arc. There may be fault systems associated with the volcanic activity. I include tectonic faults that are included in the global scale fault data set from the Coordinating Committee for Geoscience Programme in East and Southeast Asia. The most active volcano on Lombok is the Rinjani volcano. Here is a great place to learn about this volcano (the Volcano Discovery website).
If the M 6.4 earthquake was on the Flores fault, it would need to dip at about 10°. The Flores thrust fault proposed by Hengesh and Whitney (2016) has a much steeper dip. So this sequence is probably in the upper plate somewhere.
There was a M 6.0 earthquake to the east of the M 6.4, but it was much deeper (almost 600 km), so is unlikely to be genetically related to the M 6.4 sequence.Magnetic Anomalies
Historic Seismicity
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
I include some inset figures.
USGS Earthquake Pages
These are from this current sequence
These are from earlier
Other Report Pages
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
Indonesia | Sumatra Earthquake Reports
General Overview
Earthquake Reports
Social Media
pic.twitter.com/drvvxcZAis
-El Sismo ha destruido viviendas como era probable , especialmente las de Construcción no asísmica. #PrayforIndonesia 🙏 pic.twitter.com/jWDzUSAUiB
References: