Earthquake Report: M 7.1 Sumatra, Indonesia

As I completed the Earthquake Report for yesterday’s M 7.1 earthquake along the Kermadec Trench, I tweeted the report and interpretive poster to notice a colleague had tweeted about a magnitude M 7.1 earthquake about an hour earlier.

So, I got to work on this report.

https://earthquake.usgs.gov/earthquakes/eventpage/us7000jvl3/executive

Needless to say, I am a little tired. So, I will write this up more tomorrow.

Until then, I present the interpretive poster for this earthquake below.

Here is a fantastic view of this plate boundary from a low-angle oblique perspective. The geologists at the EOS Singapore prepared this.

This M7.1 earthquake happened along the plate boundary megathrust subduction zone fault (labeled Sunda megathrust in the illustration).

The location was near the “t” in the Mentawai fault label.


Below is my interpretive poster for this earthquake

  • I plot the seismicity from the past month, with diameter representing magnitude (see legend). I include earthquake epicenters from 1923-2023 with magnitudes M ≥ 7.0 in one version.
  • 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. I have improved these posters over time and some of this background information applies to the older posters.
  • Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.

    I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

  • In the upper left corner is a map showing the tectonic plates and their boundaries.
  • In the lower right corner is a map that shows the earthquake intensity using the modified Mercalli intensity scale. Earthquake intensity is a measure of how strongly the Earth shakes during an earthquake, so gets smaller the further away one is from the earthquake epicenter. The map colors represent a model of what the intensity may be. The USGS has a system called “Did You Feel It?” (DYFI) where people enter their observations from the earthquake and the USGS calculates what the intensity was for that person. The dots with yellow labels show what people actually felt in those different locations.
  • In the lower left corner is a plot that shows the same intensity (both modeled and reported) data as displayed on the map. Note how the intensity gets smaller with distance from the earthquake.
  • In the upper right corner are two maps showing the probability of earthquake triggered landslides and possibility of earthquake induced liquefaction. I will describe these phenomena below
  • Here is the map with 3 month’s seismicity plotted.

Shaking Intensity

  • Here is a figure that shows a more detailed comparison between the modeled intensity and the reported intensity. Both data use the same color scale, the Modified Mercalli Intensity Scale (MMI). More about this can be found here. The colors and contours on the map are results from the USGS modeled intensity. The DYFI data are plotted as colored dots (color = MMI, diameter = number of reports).
  • In the upper panel is the USGS Did You Feel It reports map, showing reports as colored dots using the MMI color scale. Underlain on this map are colored areas showing the USGS modeled estimate for shaking intensity (MMI scale).
  • In the lower panel is a plot showing MMI intensity (vertical axis) relative to distance from the earthquake (horizontal axis). The models are represented by the green and orange lines. The DYFI data are plotted as light blue dots. The mean and median (different types of “average”) are plotted as orange and purple dots. Note how well the reports fit the green line (the model that represents how MMI works based on quakes in California).
  • Below the lower plot is the USGS MMI Intensity scale, which lists the level of damage for each level of intensity, along with approximate measures of how strongly the ground shakes at these intensities, showing levels in acceleration (Peak Ground Acceleration, PGA) and velocity (Peak Ground Velocity, PGV).

Potential for Ground Failure

Luckily I updated this page because I noticed that the interpretive figure below was incorrect (it was for a different earthquake).

  • Below are a series of maps that show the potential for landslides and liquefaction. These are all USGS data products.
    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.

  • 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.

  • Below is the liquefaction susceptibility and landslide probability map (Jessee et al., 2017; Zhu 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.
  • I use the same color scheme that the USGS uses on their website. Note how the areas that are more likely to have experienced earthquake induced liquefaction are in the valleys. Learn more about how the USGS prepares these model results here.

Other Report Pages

Some Relevant Discussion and Figures

  • Here is my map. I include the references below in blockquote.

  • Sumatra core location and plate setting map with sedimentary and erosive systems figure. A. India-Australia plate subducts northeastwardly beneath the Sunda plate (part of Eurasia) at modern rates (GPS velocities are based on regional modeling of Bock et al, 2003 as plotted in Subarya et al., 2006). Historic earthquake ruptures (Bilham, 2005; Malik et al., 2011) are plotted in orange. 2004 earthquake and 2005 earthquake 5 meter slip contours are plotted in orange and green respectively (Chlieh et al., 2007, 2008). Bengal and Nicobar fans cover structures of the India-Australia plate in the northern part of the map. RR0705 cores are plotted as light blue. SRTM bathymetry and topography is in shaded relief and colored vs. depth/elevation (Smith and Sandwell, 1997). B. Schematic illustration of geomorphic elements of subduction zone trench and slope sedimentary settings. Submarine channels, submarine canyons, dune fields and sediment waves, abyssal plain, trench axis, plunge pool, apron fans, and apron fan channels are labeled here. Modified from Patton et al. (2013 a).

  • This is the main figure from Hayes et al. (2013) from the Seismicity of the Earth series. There is a map with the slab contours and seismicity both colored vs. depth. There are also some cross sections of seismicity plotted, with locations shown on the map.

  • Here is a great figure from Philobosian et al. (2014) that shows the slip patches from the subduction zone earthquakes in this region.

  • Map of Southeast Asia showing recent and selected historical ruptures of the Sunda megathrust. Black lines with sense of motion are major plate-bounding faults, and gray lines are seafloor fracture zones. Motions of Australian and Indian plates relative to Sunda plate are from the MORVEL-1 global model [DeMets et al., 2010]. The fore-arc sliver between the Sunda megathrust and the strike-slip Sumatran Fault becomes the Burma microplate farther north, but this long, thin strip of crust does not necessarily all behave as a rigid block. Sim = Simeulue, Ni = Nias, Bt = Batu Islands, and Eng = Enggano. Brown rectangle centered at 2°S, 99°E delineates the area of Figure 3, highlighting the Mentawai Islands. Figure adapted from Meltzner et al. [2012] with rupture areas and magnitudes from Briggs et al. [2006], Konca et al. [2008], Meltzner et al. [2010], Hill et al. [2012], and references therein.

  • This is a figure from Philobosian et al. (2012) that shows a larger scale view for the slip patches in this region. Note that today’s earthquake happened at the edge of the 7.9 earthquake slip patch.

  • Recent and ancient ruptures along the Mentawai section of the Sunda megathrust. Colored patches are surface projections of 1-m slip contours of the deep megathrust ruptures on 12–13 September 2007 (pink to red) and the shallow rupture on 25 October 2010 (green). Dashed rectangles indicate roughly the sections that ruptured in 1797 and 1833. Ancient ruptures are adapted from Natawidjaja et al. [2006] and recent ones come from Konca et al. [2008] and Hill et al. (submitted manuscript, 2012). Labeled points indicate coral study sites Sikici (SKC), Pasapuat (PSP), Simanganya (SMY), Pulau Pasir (PSR), and Bulasat (BLS).

  • Here are a series of figures from Chlieh et al. (2008 ) that show their data sources and their modeling results. I include their figure captions below in blockquote.
  • This figure shows the coupling model (on the left) and the source data for their inversions (on the right). Their source data are vertical deformation rates as measured along coral microattols. These are from data prior to the 2004 SASZ earthquake.

  • Distribution of coupling on the Sumatra megathrust derived from the formal inversion of the coral and of the GPS data (Tables 2, 3, and 4) prior to the 2004 Sumatra-Andaman earthquake (model I-a in Table 7). (a) Distribution of coupling on the megathrust. Fully coupled areas are red, and fully creeping areas are white. Three strongly coupled patches are revealed beneath Nias island, Siberut island, and Pagai island. The annual moment deficit rate corresponding to that model is 4.0 X 10^20 N m/a. (b) Observed (black vectors) and predicted (red vectors) horizontal velocities appear. Observed and predicted vertical displacements are shown by color-coded large and small circles, respectively. The Xr^2 of this model is 3.9 (Table 7).

  • This is a similar figure, but based upon observations between June 2005 and October 2006.

  • Distribution of coupling on the Sumatra megathrust derived from the formal inversion of the horizontal velocities and uplift rates derived from the CGPS measurements at the SuGAr stations (processed at SOPAC). To reduce the influence of postseismic deformation caused by the March 2005 Nias-Simeulue rupture, velocities were determined for the period between June 2005 and October 2006. (a) Distribution of coupling on the megathrust. Fully coupled areas are red and fully creeping areas are white. This model reveals strong coupling beneath the Mentawai Islands (Siberut, Sipora, and Pagai islands), offshore Padang city, and suggests that the megathrust south of Bengkulu city is creeping at the plate velocity. (b) Comparison of observed (green) and predicted (red) velocities. The Xr^2 associated to that model is 24.5 (Table 8).

  • This is a similar figure, but based on all the data.

  • Distribution of coupling on the Sumatra megathrust derived from the formal inversion of all the data (model J-a, Table 8). (a) Distribution of coupling on the megathrust. Fully coupled areas are red, and fully creeping areas are white. This model shows strong coupling beneath Nias island and beneath the Mentawai (Siberut, Sipora and Pagai) islands. The rate of accumulation of moment deficit is 4.5 X 10^20 N m/a. (b) Comparison of observed (black arrows for pre-2004 Sumatra-Andaman earthquake and green arrows for post-2005 Nias earthquake) and predicted velocities (in red). Observed and predicted vertical displacements are shown by color-coded large and small circles (for the corals) and large and small diamonds (for the CGPS), respectively. The Xr^2 of this model is 12.8.

  • Here is the figure I included in the poster above.

  • Comparison of interseismic coupling along the megathrust with the rupture areas of the great 1797, 1833, and 2005 earthquakes. The southernmost rupture area of the 2004 Sumatra-Andaman earthquake lies north of our study area and is shown only for reference. Epicenters of the 2007 Mw 8.4 and Mw 7.9 earthquakes are also shown for reference. (a) Geometry of the locked fault zone corresponding to forward model F-f (Figure 6c). Below the Batu Islands, where coupling occurs in a narrow band, the largest earthquake for the past 260 years has been a Mw 7.7 in 1935 [Natawidjaja et al., 2004; Rivera et al., 2002]. The wide zones of coupling, beneath Nias, Siberut, and Pagai islands, coincide well with the source of great earthquakes (Mw > 8.5) in 2005 from Konca et al. [2007] and in 1797 and 1833 from Natawidjaja et al. [2006]. The narrow locked patch beneath the Batu islands lies above the subducting fossil Investigator Fracture Zone. (b) Distribution of interseismic coupling corresponding to inverse model J-a (Figure 10). The coincidence of the high coupling area (orange-red dots) with the region of high coseismic slip during the 2005 Nias-Simeulue earthquake suggests that strongly coupled patches during interseismic correspond to seismic asperities during megathrust ruptures. The source regions of the 1797 and 1833 ruptures also correlate well with patches that are highly coupled beneath Siberut, Sipora, and Pagai islands.

  • Here is the Chlieh et al. (2008) figure with the 18 November 2022 M 6.9 earthquake plotted as a blue star.
  • Note how the M 6.9 happened in a region of low seismogenic coupling. Beware that this is also in an area without any geodetic (GPS/GNSS) nor paleogeodetic (coral microattol) observations (the sources of data for the coupling model).

  • This figure shows the authors’ estimate for the moment deficit in this region of the subduction zone. This is an estimate of how much the plate convergence rate, that is estimated to accumulate as tectonic strain, will need to be released during subduction zone earthquakes.

  • Latitudinal distributions of seismic moment released by great historical earthquakes and of accumulated deficit of moment due to interseismic locking of the plate interface. Values represent integrals over half a degree of latitude. Accumulated interseismic deficits since 1797, 1833, and 1861 are based on (a) model F-f and (b) model J-a. Seismic moments for the 1797 and 1833 Mentawai earthquakes are estimated based on the work by Natawidjaja et al. [2006], the 2005 Nias-Simeulue earthquake is taken from Konca et al. [2007], and the 2004 Sumatra-Andaman earthquake is taken from Chlieh et al. [2007]. Postseismic moments released in the month that follows the 2004 earthquake and in the 11 months that follows the Nias-Simeulue 2005 earthquake are shown in red and green, respectively, based on the work by Chlieh et al. [2007] and Hsu et al. [2006].

  • For a review of the 2004 and 2005 Sumatra Andaman subduction zone (SASZ) earthquakes, please check out my Earthquake Report here. Below is the poster from that report. On that report page, I also include some information about the 2012 M 8.6 and M 8.2 Wharton Basin earthquakes.
    • I include some inset figures in the poster.
    • In the upper left corner, I include a map that shows the extent of historic earthquakes along the SASZ offshore of Sumatra. This map is a culmination of a variety of papers (summarized and presented in Patton et al., 2015).
    • In the upper right corner I include a figure that is presented by Chlieh et al. (2007). These figures show model results from several models. Each model is represented by a map showing the amount that the fault slipped in particular regions. I present this figure below.
    • In the lower right corner I present a figure from Prawirodirdjo et al. (2010). This figure shows the coseismic vertical and horizontal motions from the 2004 and 2005 earthquakes as measured at GPS sites.
    • In the lower left corner are the MMI intensity maps for the two SASZ earthquakes. Note these are at different map scales. I also include the MMI attenuation curves for these earthquakes below the maps. These plots show the reported MMI intensity data as they relate to two plots of modeled estimates (the orange and green lines). These green dots are from the USGS “Did You Feel It?” reports compared to the estimates of ground shaking from Ground Motion Prediction Equation (GMPE) estimates. GMPE are empirical relations between earthquakes and recorded seismologic observations from those earthquakes, largely controlled by distance to the fault, ray path (direction and material properties), and site effects (the local geology). When seismic waves propagate through sediment, the magnitude of the ground motions increases in comparison to when seismic waves propagate through bedrock. The orange line is a regression of data for the central and eastern US and the green line is a regression through data from the western US.


  • Here is a map from Jacob et a. (2014) that shows the structure of the eastern Indian Ocean. Figure text below.

  • Free-air gravity anomaly map derived from satellite altimetry [Sandwell and Smith, 2009] over the Wharton Basin area.

  • Here is the map from Jacobs et a. (2014). Figure text below.

  • Structure and age of the Wharton Basin deduced from free-air gravity anomaly [Sandwell and Smith, 2009; background colors] for the fracture zones (thin black longitudinal lines), and marine magnetic anomaly profiles (not shown) for the isochrons (thin black latitudinal lines). The plain colors represent the oceanic lithosphere created during normal geomagnetic polarity intervals (see legend for the ages of Chrons 20 to 34 according to the time scale of Gradstein et al. [2004]). Compartments separated by major fracture zones are labeled A to H. Grey areas: oceanic plateaus, thick black line: Sunda Trench subduction zone.

  • This is a fascinating figure from Jacob et al. (2014). This shows a reconstruction of the magntic anomalies for the oceanic crust as they are subducted beneath Eurasia.

  • Reconstitution of the subducted magnetic isochrons and fracture zones of the northern Wharton Basin using the finite rotation parameters deduced from our two- and three-plate reconstructions. (a) First the geometry is restored on the Earth surface, then (b) it is draped on the top of the subducting plate as derived from seismic tomography [Pesicek et al., 2010] shown by the thin dotted lines at intervals of 100 km (b). Colored dots: identified magnetic anomalies; colored triangles: rotated magnetic anomalies, solid lines; observed fracture zones and isochrons, dashed lines: uncertain or reconstructed fracture zones, dotted lines: reconstructed isochrons from rotated magnetic anomalies (two-plate and three-plate reconstructions), colored area: oceanic lithosphere created during normal geomagnetic polarity intervals (see legend for the ages; the colored areas without solid or dotted lines have been interpolated), grey areas: oceanic plateaus, thick line: Sunda Trench subduction zone.

  • Finally, these authors present what their reconstruction implicates about this plate boundary system.

  • The deviation of the Sunda Trench from a regular arc shape (dotted lines) off Sumatra is explained by the presence of the younger, hotter and therefore lighter lithosphere in compartments C–F, which resists subduction and form an indentor (solid line). The very young compartment G was probably part of this indentor before oceanic crust formed at slow spreading rate near the Wharton fossil spreading center approached subduction: The weaker rheology of outcropping or shallow serpentinite may have favored the restoration of the accretionary prism in this area. Further south, the deviation off Java is explained by the resistance of the thicker Roo Rise, an oceanic plateau entering the subduction.

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.

Tsunami Hazard

  • Here are two maps that show the results of probabilistic tsunami modeling for the nation of Indonesia (Horspool et al., 2014). These results are similar to results from seismic hazards analysis and maps. The color represents the chance that a given area will experience a certain size tsunami (or larger).
  • The first map shows the annual chance of a tsunami with a height of at least 0.5 m (1.5 feet). The second map shows the chance that there will be a tsunami at least 3 meters (10 feet) high at the coast.

  • 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).

    References:

    Basic & General References

  • 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
  • Specific References

  • Andrade, V. and Rajendran, K., 2014. The April 2012 Indian Ocean earthquakes: Seismotectonic context and implications for their mechanisms in Tectonophysics, v. 617, p. 126-139, http://dx.doi.org/10.1016/j.tecto.2014.01.024
  • Heidarzadeh, M., Harada, T., Satake, K., Ishibe, T., Takagawa, T., 2017. Tsunamis from strike-slip earthquakes in the Wharton Basin, northeast Indian Ocean: March 2016 Mw7.8 event and its relationship with the April 2012 Mw 8.6 event in GJI, v. 2110, p. 1601-1612, doi: 10.1093/gji/ggx395
  • Jacob, J., J. Dyment, and V. Yatheesh, 2014. Revisiting the structure, age, and evolution of the Wharton Basin to better understand subduction under Indonesia, J. Geophys. Res. Solid Earth, 119, 169–190, doi:10.1002/2013JB010285.
  • Yadav, R.K., Kundu, B., Gahalaut, K., Catherine, J., Gahalaut, V.K., Ambikapathy, A., and Naidu, MZ.S., 2013. Coseismic offsets due to the 11 April 2012 Indian Ocean earthquakes (Mw 8.6 and 8.2) derived from GPS measurements in Geophysical Research Letters, v. 40, p. 3389-3393, doi:10.1002/grl.50601
  • Wiseman, K. and Bürgmann, R., 2012. Stress triggering of the great Indian Ocean strike-slip earthquakes in a diffuse plate boundary zone in Geophysical research Letters, v. 39, L22304, doi:10.1029/2012GL053954
  • Abercrombie, R.E., Antolik, M., Ekstrom, G., 2003. The June 2000 Mw 7.9 earthquakes south of Sumatra: Deformation in the India–Australia Plate. Journal of Geophysical Research 108, 16.
  • Bassin, C., Laske, G. and Masters, G., The Current Limits of Resolution for Surface Wave Tomography in North America, EOS Trans AGU, 81, F897, 2000.
  • Bock, Y., Prawirodirdjo, L., Genrich, J.F., Stevens, C.W., McCaffrey, R., Subarya, C., Puntodewo, S.S.O., Calais, E., 2003. Crustal motion in Indonesia from Global Positioning System measurements: Journal of Geophysical Research, v. 108, no. B8, 2367, doi: 10.1029/2001JB000324.
  • Bothara, J., Beetham, R.D., Brunston, D., Stannard, M., Brown, R., Hyland, C., Lewis, W., Miller, S., Sanders, R., Sulistio, Y., 2010. General observations of effects of the 30th September 2009 Padang earthquake, Indonesia. Bulletin of the New Zealand Society for Earthquake Engineering 43, 143-173.
  • Chlieh, M., Avouac, J.-P., Hjorleifsdottir, V., Song, T.-R.A., Ji, C., Sieh, K., Sladen, A., Hebert, H., Prawirodirdjo, L., Bock, Y., Galetzka, J., 2007. Coseismic Slip and Afterslip of the Great (Mw 9.15) Sumatra-Andaman Earthquake of 2004. Bulletin of the Seismological Society of America 97, S152-S173.
  • Chlieh, M., Avouac, J.P., Sieh, K., Natawidjaja, D.H., Galetzka, J., 2008. Heterogeneous coupling of the Sumatran megathrust constrained by geodetic and paleogeodetic measurements: Journal of Geophysical Research, v. 113, B05305, doi: 10.1029/2007JB004981.
  • DEPLUS, C. et al., 1998 – Direct evidence of active derormation in the eastern Indian oceanic plate, Geology.
  • DYMENT, J., CANDE, S.C. & SINGH, S., 2007 – Oceanic lithosphere subducting beneath the Sunda Trench: the Wharton Basin revisited. European Geosciences Union General Assembly, Vienna, 15-20/05.
  • Hayes, G. P., Wald, D. J., and Johnson, R. L., 2012. Slab1.0: A three-dimensional model of global subduction zone geometries in J. Geophys. Res., 117, B01302, doi:10.1029/2011JB008524.
  • Hayes, G.P., Bernardino, Melissa, Dannemann, Fransiska, Smoczyk, Gregory, Briggs, Richard, Benz, H.M., Furlong, K.P., and Villaseñor, Antonio, 2013. Seismicity of the Earth 1900–2012 Sumatra and vicinity: U.S. Geological Survey Open-File Report 2010–1083-L, scale 1:6,000,000, https://pubs.usgs.gov/of/2010/1083/l/.
  • JACOB, J., DYMENT, J., YATHEESH, V. & BHATTACHARYA, G.C., 2009 – Marine magnetic anomalies in the NE Indian Ocean: the Wharton and Central Indian basins revisited. European Geosciences Union General Assembly, Vienna, 19-24/04.
  • Ji, C., D.J. Wald, and D.V. Helmberger, Source description of the 1999 Hector Mine, California earthquake; Part I: Wavelet domain inversion theory and resolution analysis, Bull. Seism. Soc. Am., Vol 92, No. 4. pp. 1192-1207, 2002.
  • Ishii, M., Shearer, P.M., Houston, H., Vidale, J.E., 2005. Extent, duration and speed of the 2004 Sumatra-Andaman earthquake imaged by the Hi-Net array. Nature 435, 933.
  • Kanamori, H., Rivera, L., Lee, W.H.K., 2010. Historical seismograms for unravelling a mysterious earthquake: The 1907 Sumatra Earthquake. Geophysical Journal International 183, 358-374.
  • Konca, A.O., Avouac, J., Sladen, A., Meltzner, A.J., Sieh, K., Fang, P., Li, Z., Galetzka, J., Genrich, J., Chlieh, M., Natawidjaja, D.H., Bock, Y., Fielding, E.J., Ji, C., Helmberger, D., 2008. Partial Rupture of a Locked Patch of the Sumatra Megathrust During the 2007 Earthquake Sequence. Nature 456, 631-635.
  • Maus, S., et al., 2009. EMAG2: A 2–arc min resolution Earth Magnetic Anomaly Grid compiled from satellite, airborne, and marine magnetic measurements, Geochem. Geophys. Geosyst., 10, Q08005, doi:10.1029/2009GC002471.
  • Malik, J.N., Shishikura, M., Echigo, T., Ikeda, Y., Satake, K., Kayanne, H., Sawai, Y., Murty, C.V.R., Dikshit, D., 2011. Geologic evidence for two pre-2004 earthquakes during recent centuries near Port Blair, South Andaman Island, India: Geology, v. 39, p. 559-562.
  • Meltzner, A.J., Sieh, K., Chiang, H., Shen, C., Suwargadi, B.W., Natawidjaja, D.H., Philobosian, B., Briggs, R.W., Galetzka, J., 2010. Coral evidence for earthquake recurrence and an A.D. 1390–1455 cluster at the south end of the 2004 Aceh–Andaman rupture. Journal of Geophysical Research 115, 1-46.
  • Meng, L., Ampuero, J.-P., Stock, J., Duputel, Z., Luo, Y., and Tsai, V.C., 2012. Earthquake in a Maze: Compressional Rupture Branching During the 2012 Mw 8.6 Sumatra Earthquake in Science, v. 337, p. 724-726.
  • Natawidjaja, D.H., Sieh, K., Chlieh, M., Galetzka, J., Suwargadi, B., Cheng, H., Edwards, R.L., Avouac, J., Ward, S.N., 2006. Source parameters of the great Sumatran megathrust earthquakes of 1797 and 1833 inferred from coral microatolls. Journal of Geophysical Research 111, 37.
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  • Prawirodirdjo, P., McCaffrey,R., Chadwell, D., Bock, Y, and Subarya, C., 2010. Geodetic observations of an earthquake cycle at the Sumatra subduction zone: Role of interseismic strain segmentation, JOURNAL OF GEOPHYSICAL RESEARCH, v. 115, B03414, doi:10.1029/2008JB006139
  • Rivera, L., Sieh, K., Helmberger, D., Natawidjaja, D.H., 2002. A Comparative Study of the Sumatran Subduction-Zone Earthquakes of 1935 and 1984. BSSA 92, 1721-1736.
  • Shearer, P., and Burgmann, R., 2010. Lessons Learned from the 2004 Sumatra-Andaman Megathrust Rupture, Annu. Rev. Earth Planet. Sci. v. 38, pp. 103–31
  • SATISH C. S, CARTON H, CHAUHAN A.S., et al., 2011 – Extremely thin crust in the Indian Ocean possibly resulting from Plume-Ridge Interaction, Geophysical Journal International.
  • Sieh, K., Natawidjaja, D.H., Meltzner, A.J., Shen, C., Cheng, H., Li, K., Suwargadi, B.W., Galetzka, J., Philobosian, B., Edwards, R.L., 2008. Earthquake Supercycles Inferred from Sea-Level Changes Recorded in the Corals of West Sumatra. Science 322, 1674-1678.
  • Singh, S.C., Carton, H.L., Tapponnier, P, Hananto, N.D., Chauhan, A.P.S., Hartoyo, D., Bayly, M., Moeljopranoto, S., Bunting, T., Christie, P., Lubis, H., and Martin, J., 2008. Seismic evidence for broken oceanic crust in the 2004 Sumatra earthquake epicentral region, Nature Geoscience, v. 1, pp. 5.
  • Smith, W.H.F., Sandwell, D.T., 1997. Global seafloor topography from satellite altimetry and ship depth soundings: Science, v. 277, p. 1,957-1,962.
  • Sorensen, M.B., Atakan, K., Pulido, N., 2007. Simulated Strong Ground Motions for the Great M 9.3 Sumatra–Andaman Earthquake of 26 December 2004. BSSA 97, S139-S151.
  • Subarya, C., Chlieh, M., Prawirodirdjo, L., Avouac, J., Bock, Y., Sieh, K., Meltzner, A.J., Natawidjaja, D.H., McCaffrey, R., 2006. Plate-boundary deformation associated with the great Sumatra–Andaman earthquake: Nature, v. 440, p. 46-51.
  • Tolstoy, M., Bohnenstiehl, D.R., 2006. Hydroacoustic contributions to understanding the December 26th 2004 great Sumatra–Andaman Earthquake. Survey of Geophysics 27, 633-646.
  • Zhu, Lupei, and Donald V. Helmberger. “Advancement in source estimation techniques using broadband regional seismograms.” Bulletin of the Seismological Society of America 86.5 (1996): 1634-1641.

Return to the Earthquake Reports page.

Earthquake Report: M 7.1 Kermadec

I am currently taking a break following an excellent Seismological Society of America Meeting in San Juan Puerto Rico.

I presented a couple posters and one talk on the results from our USGS Powell Center meeting where we developed a basic logic tree for probabilistic tsunami hazard assessment for the Cascadia subduction zone.

Last night (my time, in Arecibo) there was an earthquake along the subduction zone, a convergent plate boundary, that forms the Kermadec trench (a deep sea trench, much like the Mariana trench).

Initially, there was one M 7.3 earthquake. I received a text message from the National Tsunami Warning Center stating that there was no tsunami risk for California, Oregon, Washington, British Columbia, and Alaska.

https://earthquake.usgs.gov/earthquakes/eventpage/us6000k6mg/executive

Shortly after that, there were then two M7.3 earthquakes. One was located east of the trench (an earthquake within the Pacific plate, much like the March 2023 M 7.3 earthquake, which was also in a similar location). The other earthquake was located west of the trench and had a depth that suggested it was a megathrust subduction zone earthquake.

Because these earthquakes happened at nearly the same time and had the same magnitude, I suspected that they were actually the same earthquake but had been automatically located in two locations (possibly due to something about the seismic waves that complicated the automatic location algorithm). In a few minutes, this was all worked out and the two earthquake pages began to show the same information, a single M 7.3 that was a subduction zone interface earthquake (an earthquake that slipped the megathrust fault).

Within a few more minutes, the magnitude was revised to be M 7.1. This is a much smaller earthquake than a M 7.3 but still quite significant. People on Raoul Island, about 75 km from the epicenter, reported strong ground shaking (intensity MMI 8, though initially reported as MMI 9).

After a few tweets, I went over to the tide gage websites that I monitor when there are subduction zone earthquakes. I often look at the UNESCO Sea Level Monitoring Facility website first. There is a map and one may click on the dots that represent most of the tide gages around the globe.

This page provides basic information about water surface elevations. One may take a quick look to see if there are excursions in the sea level data, possibly related to tsunami.

Then, when I am ready to download some data so that I may plot these data I head over to the European Commission World Sea Levels website. This is also a map interface and it takes a little more effort to learn how to operate the website to obtain the data one likes. These data are in a better format than the UNESCO site since they provide the observations, the tide prediction, and the excursion (i.e., the tsunami with the tide data removed).

I prefer to prepare my own plots so that I can control their graphical composition, these organizations create plots automatically and they are not always the best looking; I download these data, open them in excel, plot, then place them in adobe illustrator so that I can annotate them.

OK, back to the earthquake.

There was a magnitude M8.1 subduction zone earthquake in this area on 4 March 2021. Here is my poster for that earthquake, where I show that several large earthquakes happened closely in space and in time. It was phenomenal that these 3 earthquakes also generated 3 tsunami that showed up on tide gages across the south Pacific.

Yesterday’s M 7.1 happened within the area of aftershocks from the M 8.1. So, I interpret this to be an aftershock of the M8.1. (Though I could easily be convinced that it was instead simply a triggered earthquake; it also followed the 15 March 2023 M 7.0 earthquake which was directly east of yesterday’s M 7.1.

The earlier M 8.1 and yesterday’s M 7.1 earthquakes were along the subduction zone, where the Pacific plate subducts beneath the Australia plate. This subduction zone is quite active with many analogical historical earthquakes of similar magnitude in this area and also further to the north and to the south.

We may recall the 15 January 2022 Hunga Tonga eruption that generated a large trans-Pacific tsunami. Here is my report on that event. Here is a web page that I put together for the California Geological Survey where I serve the public in the Seismic Hazards Program and Tsunami Unit (actually, I cannot share that page as it does not work outside of the USA, sadly; I will add a link once I am back home).

At the bottom of this report are a series of tweets that include some additional educational material. Check out the EarthScope Consortium tweets!

Below is my interpretive poster for this earthquake

  • I plot the seismicity from the past month, with diameter representing magnitude (see legend). I include earthquake epicenters from 1923-2023 with magnitudes M ≥ 7.0 in one version.
  • 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. I have improved these posters over time and some of this background information applies to the older posters.
  • Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.

    I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

  • In the upper left corner is a map that shows the major plate tectonic boundaries.
  • In the lower right corner is a map that shows the ground shaking from the earthquake, with color representing intensity using the Modified Mercalli Intensity (MMI) scale. The closer to the earthquake, the stronger the ground shaking. The colors on the map represent the USGS model of ground shaking. There is one location with a report from people who posted information on the USGS Did You Feel It? part of the website for this earthquake. There are things that affect the strength of ground shaking other than distance, which is why the reported intensities are different from the modeled intensities.
  • In the upper right corner is a plot that includes the 2021 M 8.1 & M 7.4 and 2023 M 7.0 earthquakes. I include the aftershocks from about one week after the M 8.1 and outline these aftershocks to show how yesterday’s M 7.1 is within this area.
  • To the left of the aftershock map I include the USGS earthquake fault slip model. The colors represent the amount of slip that this fault experienced during the earthquake. We can see that they think the fault slipped up to about 1.25 meters (about 4 feet).
  • To the left are tide gage plots from the tide gages on Raoul Island (shown on map). Anthony Lomax and I debated on Twitter about whether these signals were tsunami or seismic waves. We concluded that these are most likely tsunami waves because of their arrival time (seismic waves would have arrived sooner), their duration (seismic waves would not have lasted as long in time), and their amplitude & wave heights (seismic waves would have been smaller in size). Twitter is such a helpful place to discuss our observations in real time! I learn so much from my colleagues. It really is such a wonderful community that we have developed over the years!
  • In the lower right center is a map from Benz et al. (2011) that shows earthquakes with circles that represent magnitude (diameter) and depth (color). Deeper = blue & shallower = red. There is a cross section (cut into the earth) profile through this seismicity (the blue line J-J’). I plot the M 7.0 as a blue star.
  • To the left of the map is cross section J-J’ that shows earthquake hypocenters (3-D locations) in the region of the M 7.0 earthquake.
  • Here is the map with a month’s seismicity plotted.

Tsunami

  • Here I present the tide gage data from this earthquake and tsunami.
  • These two gages are located on opposite sides of Raoul Island. Can you tell which is on the north side and which is on the south side? Go to the tide gage websites I link to above to see if you are correct.
  • The size of the wave is similar for both of these gages (about 20 cm wave height).
  • In the legend, one may learn the difference between wave height and amplitude. Wave height is the vertical distance between the peak wave and the trough of the wave. The amplitude is the height of the wave peak above the ambient water surface (the ambient tide level).


    Some Relevant Discussion and Figures

    • Here is the map from Timm et al., 2013.

    • Bathymetric map of the Tonga–Kermadec arc system. Map showing the depth of the subducted slab beneath the Tonga–Kermadec arc system. Louisville seamount ages are after Koppers et al.49 ELSC, eastern Lau-spreading centre; DSDP, Deep Sea Drilling Programme; NHT, Northern Havre Trough; OT, Osbourn Trough; VFR, Valu Fa Ridge. Arrows mark total convergence rates.

    • Here is the tectonic map from Ballance et al., 1999.

    • Map of the Southwest Pacific Ocean showing the regional tectonic setting and location of the two dredged profiles. Depth contours in kilometres. The presently active arcs comprise New Zealand–Kermadec Ridge–Tonga Ridge, linked with Vanuatu by transforms associated with the North Fiji Basin. Colville Ridge–Lau Ridge is the remnant arc. Havre Trough–Lau Basin is the active backarc basin. Kermadec–Tonga Trench marks the site of subduction of Pacific lithosphere westward beneath Australian plate lithosphere. North and South Fiji Basins are marginal basins of late Neogene and probable Oligocene age, respectively. 5.4sK–Ar date of dredged basalt sample (Adams et al., 1994).

    • Here is a great summary of the fault mechanisms for earthquakes along this plate boundary (Yu, 2013).

    • Large subduction-zone interplate earthquakes (large open gray stars) labeled with event date, Mw, GCMT focal mechanisms, and GPS velocity vectors (gray arrows and black triangles labeled with station name). GPS velocities are listed in Table 3. Black lines indicate the Tonga–Kermadec and Vanuatu trenches. Note that the 2009/09/29 Samoa–Tonga outer trench-slope event (Mw 8.1) triggered large interplate doublets (both of Mw 7.8; Lay et al., 2010). The Pacific plate subducts westward beneath the Australian plate along the Tonga–Kermadec trench, whereas the Australian plate subducts eastward beneath the Vanuatu arc and North Fiji basin. The opposite orientation between the Tonga–Kermadec and Vanuatu subduction systems is due to complex and broad back-arc extension in the Lau and North Fiji basins (Pelletier et al., 1998).


      Regional map of moderate-sized (mb > 4:7) shallow-focus repeating earthquakes and background seismicity along the (a) Tonga–Kermadec and (b) Vanuatu (former New Hebrides) subduction zones. Shallow repeating earthquakes (black stars) and their available Global Centroid Moment Tensor (GCMT; Dziewoński et al., 1981; Ekström et al., 2003) are labeled with event date and doublet/cluster id where applicable. Colors of GCMT are used to distinguish nearby different repeaters. Source parameters for the clusters and doublets are listed in Tables 1 and 2. Background seismicity is shown as gray dots and large interplate earthquakes (moment magnitude, Mw > 7:3) since 1976 are shown as large open gray stars. Black lines indicate the trench (Bird, 2003) and slab contour at 50-km depth (Gudmundsson and Sambridge, 1998). Repeating earthquake clusters in the (a) T1 and T2 plate-interface regions in Tonga and (b) V3 plate-interface region in Vanuatu are used to study the fault-slip rate ( _d). A regional map of the Tonga–Kermadec–Vanuatu subduction zones is
      shown in the inset figure, with the gray dotted box indicating the expanded region in the main figure.

    • Here is a great visualization of the Kermadec Trench from Woods Hole.

    Kermadec Trench from Woods Hole Oceanographic Inst. on Vimeo.

    • Here is another map of the bathymetry in this region of the Kermadec trench. This was produced by Jack Cook at the Woods Hole Oceanographic Institution. The Lousiville Seamount Chain is clearly visible in this graphic.

    • I put together an animation of seismicity from 1965 – 2015 Sept. 7. Here is a map that shows the entire seismicity for this period. I plot the slab contours for the subduction zone here. These were created by the USGS (Hayes et al., 2012).

    • Here is the animation. Download the mp4 file here. This animation includes earthquakes with magnitudes greater than M 6.5 and this is the kml file that I used to make this animation.
    • Here is the oblique view of the slab from Green (2003). Some of the following figures are for the Tonga subduction zone, the same plate boundary as Kermadec, with some slightly different attributes.

    • Earthquakes and subducted slabs beneath the Tonga–Fiji area. The subducting slab and detached slab are defined by the historic earthquakes in this region: the steeply dipping surface descending from the Tonga Trench marks the currently active subduction zone, and the surface lying mostly between 500 and 680 km, but rising to 300 km in the east, is a relict from an old subduction zone that descended from the fossil Vitiaz Trench. The locations of the mainshocks of the two Tongan earthquake sequences discussed by Tibi et al. are marked in yellow (2002 sequence) and orange (1986 series). Triggering mainshocks are denoted by stars; triggered mainshocks by circles. The 2002 sequence lies wholly in the currently subducting slab (and slightly extends the earthquake distribution in it),whereas the 1986 mainshock is in that slab but the triggered series is located in the detached slab,which apparently contains significant amounts of metastable olivine

    • Here are figures from Richards et al. (2011) with their figure captions below in blockquote.
    • The main tectonic map

    • bathymetry, and major tectonic element map of the study area. The Tonga and Vanuatu subduction systems are shown together with the locations of earthquake epicenters discussed herein. Earthquakes between 0 and 70 km depth have been removed for clarity. Remaining earthquakes are color-coded according to depth. Earthquakes located at 500–650 km depth beneath the North Fiji Basin are also shown. Plate motions for Vanuatu are from the U.S. Geological Survey, and for Tonga from Beavan et al. (2002) (see text for details). Dashed line indicates location of cross section shown in Figure 3. NFB—North Fiji Basin; HFZ—Hunter Fracture Zone.

    • Here is the map showing the current configuration of the slabs in the region.

    • Map showing distribution of slab segments beneath the Tonga-Vanuatu region. West-dipping Pacifi c slab is shown in gray; northeast-dipping Australian slab is shown in red. Three detached segments of Australian slab lie below the North Fiji Basin (NFB). HFZ—Hunter Fracture Zone. Contour interval is 100 km. Detached segments of Australian plate form sub-horizontal sheets located at ~600 km depth. White dashed line shows outline of the subducted slab fragments when reconstructed from 660 km depth to the surface. When all subducted components are brought to the surface, the geometry closely approximates that of the North Fiji Basin.

    • This is the cross section showing the megathrust fault configuration based on seismic tomography and seismicity.

    • Previous interpretation of combined P-wave tomography and seismicity from van der Hilst (1995). Earthquake hypocenters are shown in blue. The previous interpretation of slab structure is contained within the black dashed lines. Solid red lines mark the surface of the Pacifi c slab (1), the still attached subducting Australian slab (2a), and the detached segment of the Australian plate (2b). UM—upper mantle;
      TZ—transition zone; LM—lower mantle.

    • Here is their time step interpretation of the slabs that resulted in the second figure above.

    • Simplified plate tectonic reconstruction showing the progressive geometric evolution of the Vanuatu and Tonga subduction systems in plan view and in cross section. Initiation of the Vanuatu subduction system begins by 10 Ma. Initial detachment of the basal part of the Australian slab begins at ca. 5–4 Ma and then sinking and collision between the detached segment and the Pacifi c slab occur by 3–4 Ma. Initial opening of the Lau backarc also occurred at this time. Between 3 Ma and the present, both slabs have been sinking progressively to their current position. VT—Vitiaz trench; dER—d’Entrecasteaux Ridge.

    References:

    Basic & General References

  • 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
  • Specific References

  • Richards, S., Holm, R., and Barber, G., 2011. Skip Nav Destination When slabs collide: A tectonic assessment of deep earthquakes in the Tonga-Vanuatu region in Geology, c. 39, no. 8, p. 787-790, https://doi.org/10.1130/G31937.1
  • Timm, C., Bassett, D., Graham, I. et al. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga–Kermadec arc. Nat Commun 4, 1720 (2013). https://doi.org/10.1038/ncomms2702

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Earthquake Report: M 7.0 Papua New Guinea

This morning (my time) I received a notification from the National Tsunami Warning Center, the organization responsible for generating notifications for my locality (California).

There was a magnitude M 7.0 earthquake in Papua New Guinea.

https://earthquake.usgs.gov/earthquakes/eventpage/at00rsi26z/executive

This earthquake was almost intermediate depth (about 63 km), not on a tsunamigenic fault, and far inland (so likely no tsunami).

There was an event last September just to the east. Here is the earthquake report for that event.

The USGS includes many products on their earthquake pages. We can see from their ground failure products that this earthquake likely generated significant liquefaction. I show this on the interpretive poster and include a write up about ground failure generated by earthquakes below.

Something that influences the liquefaction and landslide modeling is the topography. The M 7.0 earthquake happened in an area that is mostly low lying Earth adjacent to the Sepik River system. The ground is probably highly saturated with water.

Also, there is little steep topography in the area, which probably contributes to the low chance for landslides in the USGS model for earthquake triggered landslides.

As always, we hope that there was not much suffering from this earthquake. The shaking intensity was high, so it must have been quite terrifying. The region does not have a high population density, so the USGS PAGER alert estimate reflects this. There were about 133,000 people who may have been exposed to intensity MMI 7 and 333,000 exposed to MMI 6.

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 1923-2023 with magnitudes M ≥ 0.0 in one version.
  • 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. I have improved these posters over time and some of this background information applies to the older posters.
  • Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.

    I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

  • In the upper right corner is a map showing the plate tectonic boundaries (from the GEM) and seismicity from the past century (from the USGS).
  • In the lower right corner is a map that shows the earthquake intensity using the modified Mercalli intensity scale. Earthquake intensity is a measure of how strongly the Earth shakes during an earthquake, so gets smaller the further away one is from the earthquake epicenter. The map colors represent a model of what the intensity may be. The USGS has a system called “Did You Feel It?” (DYFI) where people enter their observations from the earthquake and the USGS calculates what the intensity was for that person. The dots with yellow labels show what people actually felt in those different locations.
  • In the upper left corner are two maps showing the probability of earthquake triggered landslides and possibility of earthquake induced liquefaction. I will describe these phenomena below.
  • In the lower left center is a figure from Baldwin et al. (2012). This figure shows a series of cross sections along this convergent plate boundary from the Solomon Islands in the east to Papua New Guinea in the west. Cross section ‘D’ is the most representative for the earthquakes today. I present the map and this figure again below, with their original captions. Above the map is cross section D-D’ that shows the PFTB to the south of today’s earthquake. I placed the yellow star marking today’s M 7.0 below the cross section. The faults are actually quite complex, so this schematic illustration may not be a perfect representation of the faults here.
  • In the bottom center is a profile showing the GPS velocities across the two main fault systems that profile A-A’ crosses (also shown on map). The M 7.0 is somewhere between these two fault systems (possibly along a fault that leads up to the Fold and Thrust Belt(?).
  • Here is the map with 3 month’s seismicity plotted.

Shaking Intensity

  • Here is a figure that shows a more detailed comparison between the modeled intensity and the reported intensity. Both data use the same color scale, the Modified Mercalli Intensity Scale (MMI). More about this can be found here. The colors and contours on the map are results from the USGS modeled intensity. The DYFI data are plotted as colored dots (color = MMI, diameter = number of reports).
  • In the upper panel is the USGS Did You Feel It reports map, showing reports as colored dots using the MMI color scale. Underlain on this map are colored areas showing the USGS modeled estimate for shaking intensity (MMI scale).
  • In the lower panel is a plot showing MMI intensity (vertical axis) relative to distance from the earthquake (horizontal axis). The models are represented by the green and orange lines. The DYFI data are plotted as light blue dots. The mean and median (different types of “average”) are plotted as orange and purple dots. Note how well the reports fit the green line (the model that represents how MMI works based on quakes in California).
  • Below the lower plot is the USGS MMI Intensity scale, which lists the level of damage for each level of intensity, along with approximate measures of how strongly the ground shakes at these intensities, showing levels in acceleration (Peak Ground Acceleration, PGA) and velocity (Peak Ground Velocity, PGV).

    Some Relevant Discussion and Figures

    • Here is the Holm et al. (2016) figure.

    • Topography, bathymetry and regional tectonic setting of New Guinea and Solomon Islands. Arrows indicate rate and direction of plate motion of the Australian and Pacific plates (MORVEL, DeMets et al., 2010); Mamberamo thrust belt, Indonesia (MTB); North Fiji Basin (NFB)

    • These maps from Holm et al. (2016) show the tectonic plate boundaries and plates/microplates.
    • The lower panel includes symbology for the magmatic centers associated with the different arcs analyzed in their study.


    • Tectonic setting of Papua New Guinea and Solomon Islands. a) Regional plate boundaries and tectonic elements. Light grey shading illustrates bathymetry b2000mbelow sea level indicative of continental or arc crust, and oceanic plateaus; 1000mdepth contour is also shown. Adelbert Terrane (AT); Bismarck Sea fault (BSF); Bundi fault zone (BFZ); Feni Deep (FD); Finisterre Terrane (FT); Gazelle Peninsula (GP); Kia-Kaipito-Korigole fault zone (KKKF); Lagaip fault zone (LFZ); Mamberamo thrust belt (MTB); Manus Island (MI); New Britain (NB); New Ireland (NI); North Sepik arc (NSA); Ramu-Markham fault (RMF); Weitin Fault (WF);West Bismarck fault (WBF); Willaumez-Manus Rise (WMR). b) Magmatic arcs and volcanic centers related to this study.

    • The this map and cross section pair shows the Holm et al. (2016) interpretation of the oceanic crust in this region in the current position.

    • a) Present day tectonic features of the Papua New Guinea and Solomon Islands region as shown in plate reconstructions. Sea floor magnetic anomalies are shown for the Caroline plate (Gaina and Müller, 2007), Solomon Sea plate (Gaina and Müller, 2007) and Coral Sea (Weissel and Watts, 1979). Outline of the reconstructed Solomon Sea slab (SSP) and Vanuatu slab (VS)models are as indicated. b) Cross-sections related to the present day tectonic setting. Section locations are as indicated. Bismarck Sea fault (BSF); Feni Deep (FD); Louisiade Plateau (LP); Manus Basin (MB); New Britain trench (NBT); North Bismarck microplate (NBP); North Solomon trench (NST); Ontong Java Plateau (OJP); Ramu-Markham fault (RMF); San Cristobal trench (SCT); Solomon Sea plate (SSP); South Bismarck microplate (SBP); Trobriand trough (TT); projected Vanuatu slab (VS); West Bismarck fault (WBF); West Torres Plateau (WTP); Woodlark Basin (WB).

    • Koulali et al (2015) use GPS data to resolve the kinematics of the central-eastern Papua New Guinea region. The first figure below is a map that shows the GPS velocities in this region There are two cross section profiles labeled on the map (the M 7.0 earthquake happened to the east of A-A’). Note the complicated and detailed fault mapping (the balck lines). The convergence is generally perpendicular to the PFTB in the east and more oblique to the PFTB on the western portion of this map.

    • The GPS velocity field and 95 per cent confidence interval ellipses with respect to the Australian Plate. Red and blue vectors are the new calculated field and black vectors are from Wallace et al. (2004). The dashed rectangle shows the area of Fig. 3. The blue dashed lines correspond to the location of profiles shown in Fig. 4. Note that the velocity scales for the red and blue vectors are different (see the lower right corner for scales). The black velocities are plotted at the same scale as the red vectors.

    • Here are the two profiles. The red and blue lines plot vertical land motion (VLM) rates in mm/yr and show strain accumulates across the region. Today’s earthquake happened in the region labeled ‘Highland FTB.’ The plot shows that ~5 mm/yr of strain accumulates in this fault system.

    • Profiles A–A& and B–B& from Fig. 2 showing model fit to GPS observations. Red symbols and lines are the GPS observed and modelled velocities, respectively, for the profile-normal component. Blue symbols and lines correspond to the profile-parallel component. The green and pink lines corresponds to the model using the Ramu-Markham fault geometry from Wallace et al. (2004), south of Lae. Grey profiles show the projected topography. The seismicity is from the ISC catalogue for events > Mw 3.5 (1960–2011).

    • This is the Cloos et al. (2005) map from the poster.
    • Something that came up this week during a tsunami workshop/meeting was about the activity for each plate boundary that has a potential to generate trans-Pacific tsunami impacting the U.S. and U.S. territories.
    • Over long periods of time, the plate boundaries around the world change shape. At some times, the relative plate motion between plates is localized one fault system. At other times, the active plate boundary fault is along a different fault system.
    • The map below includes information about the activity of the plate boundary faults. The active convergent zones are the New Britain subduction zone, the Ramu-Markham fault zone (RMFZ), the Seram subduction zone, part of the Papuan Fold and Thrust Belt, and parts of the New Guinea subduction zone. The strike-slip zones are the Bewani-Torricelli fault zone, the Mamberamo deformation zone, the Yapen fault zone, the Sorong fault zone, and the Tarera-Aiduna fault zone.
    • This map shows evidence for several different paleo-plate boundaries. Imagine how each subduction zone once had a pair of plates and those plates are still there. Even while inactive, earthquakes can occur on these faults.

    • Tectonic map of New Guinea, adapted from Hamilton (1979), Cooper and Taylor (1987), Dow et al. (1988), and Sapiie et al. (1999). AFTB—Aure fold and thrust belt, FTB—fold-and-thrust belt, IOB—Irian Ophiolite Belt, TFB—thrust-and-fold belt, POB—Papuan Ophiolite Belt, BTFZ—Bewani-Torricelli fault zone, MDZ—Mamberamo deformation zone, YFZ—Yapen fault zone, SFZ—Sorong fault zone, WO—Weyland overthrust. Continental basement exposures are concentrated along the southern fl ank of the Central Range: BD—Baupo Dome, MA—Mapenduma anticline, DM—Digul monocline, IDI—Idenberg Inlier, MUA—Mueller anticline, KA—Kubor anticline, LFTB—Legguru fold-and-thrust belt, RMFZ—Ramu-Markham fault zone, TAFZ—Tarera-Aiduna fault zone. The Tasman line separates continental crust that is Paleozoic and younger to the east from Precambrian to the west.

    • This is the Cloos et al. (2005) cross section, showing a different interpretation of the delaminated slab.

    • Lithospheric-scale cross section at 2 Ma. Plate motion is now focused along the Yapen fault zone in the center of the recently extinct arc. This probably occurred because this zone of weakness had a trend that could accommodate the imposed movements as the corner of the Caroline microplate ruptured, forming the Bismarck plate, and the corner of the Australian plate ruptured, forming the Solomon microplate. The collisional delamination-generated magmatic event ends in the highlands as the lower crustal magma chamber solidifies. Upwelled asthenosphere cools and transforms into lithospheric mantle. This drives a slow regional subsidence of the highlands that will continue for tens of millions of years or until other plate-tectonic movements are initiated. Deep erosion is still concentrated on the fl anks of the mountain belt. RMB—Ruffaer Metamorphic Belt, AUS—Australian plate, PAC—Pacific plate.

    • Here is the tectonic map figure from Sappie and Cloos (2004). Their work was focused on western PNG, so their interpretations are more detailed there (and perhaps less relevant for us for these eastern PNG earthquakes).

    • Seismotectonic interpretation of New Guinea. Tectonic features: PTFB—Papuan thrust-and-fold belt; RMFZ—Ramu-Markham fault zone; BTFZ—Bewani-Torricelli fault zone; MTFB—Mamberamo thrust-and-fold belt; SFZ—Sorong fault zone; YFZ—Yapen fault zone; RFZ—Ransiki fault zone; TAFZ—Tarera-Aiduna fault zone; WT—Waipona Trough. After Sapiie et al. (1999).

    • This is the two panel figure from Holm and Richards (2013) that shows how the New Britain trench megathrust splays into three thrust faults as this fault system heads onto PNG. They plot active thrust faults as black triangles (with the triangles on the hanging wall side of the fault) and inactive thrust faults as open triangles. So, either the NG trench subduction zone extends further east than is presented in earlier work or the Bundi Fault Zone is the fault associated with this deep seismicity.

    • Topography, bathymetry and major tectonic elements of the study area. (a) Major tectonic boundaries of Papua New Guinea and the western Solomon Islands; CP, Caroline plate; MB, Manus Basin; NBP, North Bismarck plate; NBT, New Britain trench; NGT, New Guinea trench; NST, North Solomon trench; PFTB, Papuan Fold and Thrust Belt; PT, Pocklington trough; RMF, Ramu-Markham Fault; SBP, South Bismarck plate; SCT, San Cristobal trench; SS, Solomon Sea plate; TT, Trobriand trough; WB,Woodlark Basin; WMT,West Melanesian trench. Study area is indicated by rectangle labelled Figure 1b; the other inset rectangle highlights location for subsequent figures. Present day GPS motions of plates are indicated relative to the Australian plate (from Tregoning et al. 1998, 1999; Tregoning 2002; Wallace et al. 2004). (b) Detailed topography, bathymetry and structural elements significant to the South Bismarck region (terms not in common use are referenced); AFB, Aure Fold Belt (Davies 2012); AT, Adelbert Terrane (e.g. Wallace et al. 2004); BFZ, Bundi Fault Zone (Abbott 1995); BSSL, Bismarck Sea Seismic Lineation; CG, Cape Gloucester; FT, Finisterre Terrane; GF, Gogol Fault (Abbott 1995); GP, Gazelle Peninsula; HP, Huon Peninsula; MB, Manus Basin; NB, New Britain; NI, New Ireland; OSF, Owen Stanley Fault; RMF, Ramu-Markham Fault; SS, Solomon Sea; WMR, Willaumez-Manus Rise (Johnson et al. 1979); WT, Wonga Thrust (Abbott et al. 1994); minor strike-slip faults are shown adjacent to Huon Peninsula (Abers & McCaffrey 1994) and in east New Britain, the Gazelle Peninsula (e.g. Madsen & Lindley 1994). Circles indicate centres of Quaternary volcanism of the Bismarck arc. Filled triangles indicate active thrusting or subduction, empty triangles indicate extinct or negligible thrusting or subduction.

    • This map shows plate velocities and euler poles for different blocks. I include the figure caption below as a blockquote.

    • Tectonic maps of the New Guinea region. (a) Seismicity, volcanoes, and plate motion vectors. Plate motion vectors relative to the Australian plate are surface velocity models based on GPS data, fault slip rates, and earthquake focal mechanisms (UNAVCO, http://jules.unavco.org/Voyager/Earth). Earthquake data are sourced from the International Seismological Center EHB Bulletin (http://www.isc.ac.uk); data represent events from January 1994 through January 2009 with constrained focal depths. Background image is generated from http://www.geomapapp.org. Abbreviations: AB, Arafura Basin; AT, Aure Trough; AyT, Ayu Trough; BA, Banda arc; BSSL, Bismarck Sea seismic lineation; BH, Bird’s Head; BT, Banda Trench; BTFZ, Bewani-Torricelli fault zone; DD, Dayman Dome; DEI, D’Entrecasteaux Islands; FP, Fly Platform; GOP, Gulf of Papua; HP, Huon peninsula; LA, Louisiade Archipelago; LFZ, Lowlands fault zone; MaT, Manus Trench; ML, Mt. Lamington; MT, Mt. Trafalgar; MuT, Mussau Trough; MV, Mt. Victory; MTB, Mamberamo thrust belt; MVF, Managalase Plateau volcanic field; NBT, New Britain Trench; NBA, New Britain arc; NF, Nubara fault; NGT, New Guinea Trench; OJP, Ontong Java Plateau; OSF, Owen Stanley fault zone; PFTB, Papuan fold-and-thrust belt; PP, Papuan peninsula; PRi, Pocklington Rise; PT, Pocklington Trough; RMF, Ramu-Markham fault; SST, South Solomons Trench; SA, Solomon arc; SFZ, Sorong fault zone; ST, Seram Trench; TFZ, Tarera-Aiduna fault zone; TJ, AUS-WDKPAC triple junction; TL, Tasman line; TT, Trobriand Trough;WD, Weber Deep;WB, Woodlark Basin;WFTB, Western (Irian) fold-and-thrust belt; WR,Woodlark Rift; WRi, Woodlark Rise; WTB, Weyland thrust; YFZ, Yapen fault zone.White box indicates the location shown in Figure 3. (b) Map of plates, microplates, and tectonic blocks and elements of the New Guinea region. Tectonic elements modified after Hill & Hall (2003). Abbreviations: ADB, Adelbert block; AOB, April ultramafics; AUS, Australian plate; BHB, Bird’s Head block; CM, Cyclops Mountains; CWB, Cendrawasih block; CAR, Caroline microplate; EMD, Ertsberg Mining District; FA, Finisterre arc; IOB, Irian ophiolite belt; KBB, Kubor & Bena blocks (including Bena Bena terrane); LFTB, Lengguru fold-and-thrust belt; MA, Mapenduma anticline; MB, Mamberamo Basin block; MO, Marum ophiolite belt; MHS, Manus hotspot; NBS, North Bismarck plate; NGH, New Guinea highlands block; NNG, Northern New Guinea block; OKT, Ok Tedi mining district; PAC, Pacific plate; PIC, Porgera intrusive complex; PSP, Philippine Sea plate; PUB, Papuan Ultramafic Belt ophiolite; SB, Sepik Basin block; SDB, Sunda block; SBS, South Bismarck plate; SIB, Solomon Islands block; WP, Wandamen peninsula; WDK, Woodlark microplate; YQ, Yeleme quarries.

    • This figure incorporates cross sections and map views of various parts of the regional tectonics (Baldwin et al., 2012). These deep earthquakes are nearest the cross section D (though are much deeper than these shallow cross sections). I include the figure caption below as a blockquote.

    • Oblique block diagram of New Guinea from the northeast with schematic cross sections showing the present-day plate tectonic setting. Digital elevation model was generated from http://www.geomapapp.org. Oceanic crust in tectonic cross sections is shown by thick black-and-white hatched lines, with arrows indicating active subduction; thick gray-and-white hatched lines indicate uncertain former subduction. Continental crust, transitional continental crust, and arc-related crust are shown without pattern. Representative geologic cross sections across parts of slices C and D are marked with transparent red ovals and within slices B and E are shown by dotted lines. (i ) Cross section of the Papuan peninsula and D’Entrecasteaux Islands modified from Little et al. (2011), showing the obducted ophiolite belt due to collision of the Australian (AUS) plate with an arc in the Paleogene, with later Pliocene extension and exhumation to form the D’Entrecasteaux Islands. (ii ) Cross section of the Papuan peninsula after Davies & Jaques (1984) shows the Papuan ophiolite thrust over metamorphic rocks of AUS margin affinity. (iii ) Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent. (iv) Across the Bird’s Head, the cross section after Bailly et al. (2009) illustrates deformation in the Lengguru fold-and-thrust belt as a result of Late Miocene–Early Pliocene northeast-southwest shortening, followed by Late Pliocene–Quaternary extension. Abbreviations as in Figure 2, in addition to NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; (U)HP, (ultra)high-pressure.

    • Here is the relevant cross section from Baldwin et al. (2012).

    • Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent.

    • Here is map that shows the tectonics in and to the east of Papua New Guinea from Ott and Mann (2015).
    • These authors use seismic reflection data and onshore geologic and GPS studies to look at the formation of the Aure-Moresby and Papuan fold and thrust belts.

    • Active tectonic setting of eastern Papua New Guinea showing the boundaries of the Woodlark microplate that includes previously proposed oceanic Solomon Sea plate, the Trobriand platform, and the Woodlark plate [Wallace et al., 2014]. The New Britain trench along the northern margin of the Woodlark plate is a rapidly subducting, 600 km long slab that generates a strong pull on the unsubducted Woodlark microplate [Weissel et al., 1982; Wallace et al., 2004, 2014]. Small circles around the Trobriand platform/Australia pole predict the described pattern of transpressional deformation along the Aure-Moresby fold-thrust belt and the formation of the adjacent, late Miocene to Recent Aure-Moresby foreland basin. Approximate location of the downdip limits of the subducted Solomon Sea slabs are shown by dashed lines and modified from Pegler et al. [1995], Woodhead et al. [2010], and Hayes et al. [2012]. Earthquake data are provided courtesy of the U.S. Geological Survey. Note that the tapering triangular shape of the extension in the Woodlark basin closely matches the size and shape of the thrusting observed in the Aure-Moresby fold-thrust belt and foreland basin.

Potential for Ground Failure

Luckily I updated this page because I noticed that the interpretive figure below was incorrect (it was for a different earthquake).

  • Below are a series of maps that show the potential for landslides and liquefaction. These are all USGS data products.
    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.

  • 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.

  • Below is the liquefaction susceptibility and landslide probability map (Jessee et al., 2017; Zhu 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.
  • I use the same color scheme that the USGS uses on their website. Note how the areas that are more likely to have experienced earthquake induced liquefaction are in the valleys. Learn more about how the USGS prepares these model results here.

    References:

    Basic & General References

  • 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
  • Specific References

  • Abers, G. and McCaffrey, R., 1988. Active Deformation in the New Guinea Fold-and-Thrust Belt: Seismological Evidence for Strike-Slip Faulting and Basement-Involved Thrusting in JGR, v. 93, no. B11, p. 13,332-13,354
  • Baldwin, S.L., Monteleone, B.D., Webb, L.E., Fitzgerald, P.G., Grove, M., and Hill, E.J., 2004. Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea in Nature, v. 431, p/ 263-267, doi:10.1038/nature02846.
  • Baldwin, S.L., Fitzgerald, P.G., and Webb, L.E., 2012. Tectonics of the New Guinea Region, Annu. Rev. Earth Planet. Sci., v. 40, pp. 495-520.
  • Cloos, M., Sapiie, B., Quarles van Ufford, A., Weiland, R.J., Warren, P.Q., and McMahon, T.P., 2005. Collisional delamination in New Guinea: The geotectonics of subducting slab breakoff: Geological Society of America Special Paper 400, 51 p., doi: 10.1130/2005.2400.
  • Dow, D.B., 1977. A Geological Synthesis of Papua New Guinea, Bureau of Mineral Resources, Geology, and Geophysics, Bulltein 201, Australian Government Publishing Sevice, Canberra, 1977, 58 pp.
  • ..

  • Hamilton, W.B., 1979. Tectonics of the Indonesian Region, USGS Professional Paper 1078.
  • Holm, R. and Richards, S.W., 2013. A re-evaluation of arc-continent collision and along-arc variation in the Bismarck Sea region, Papua New Guinea in Australian Journal of Earth Sciences, v. 60, p. 605-619.
  • Holm, R.J., Richards, S.W., Rosenbaum, G., and Spandler, C., 2015. Disparate Tectonic Settings for Mineralisation in an Active Arc, Eastern Papua New Guinea and the Solomon Islands in proceedings from PACRIM 2015 Congress, Hong Kong ,18-21 March, 2015, pp. 7.
  • Holm, R.J., Rosenbaum, G., Richards, S.W., 2016. Post 8 Ma reconstruction of Papua New Guinea and Solomon Islands: Microplate tectonics in a convergent plate boundary setting in Eartth Science Reviews, v. 156, p. 66-81.
  • Johnson, R.W., 1976, Late Cainozoic volcanism and plate tectonics at the southern margin of the Bismarck Sea, Papua New Guinea, in Johnson, R.W., ed., 1976, Volcanism in Australia: Amsterdam, Elsevier, p. 101-116
  • Koulali, A., tregoning, P., McClusky, S., Stanaway, R., Wallace, L., and Lister, G., 2015. New Insights into the present-day kinematics of the central and western Papua New Guinea from GPS in GJI, v. 202, p. 993-1004, doi: 10.1093/gji/ggv200
  • Ott, B., and P. Mann (2015), Late Miocene to Recent formation of the Aure-Moresby fold-thrust belt and foreland basin as a consequence of Woodlark microplate rotation, Papua New Guinea, Geochem. Geophys. Geosyst., 16, 1988–2004, http://dx.doi.org/10.1002/2014GC005668
  • Sapiie, B., and Cloos, M., 2004. Strike-slip faulting in the core of the Central Range of west New Guinea: Ertsberg Mining District, Indonesia in GSA Bulletin, v. 116; no. 3/4; p. 277–293
  • Tregoning, P., McQueen, H., Lambeck, K., Jackson, R. Little, T., Saunders, S., and Rosa, R., 2000. Present-day crustal motion in Papua New Guinea, Earth Planets and Space, v. 52, pp. 727-730.

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