I don’t always have the time to write a proper Earthquake Report. However, I prepare interpretive posters for these events.
Because of this, I present Earthquake Report Lite. (but it is more than just water, like the adult beverage that claims otherwise). I will try to describe the figures included in the poster, but sometimes I will simply post the poster here.
On 14 August ’21 there was a magnitude M 7.2 oblique strike-slip earthquake in Haiti. This earthquake was along the Enriquillo-Plantain Garden fault zone, which also ruptured in 2010. Here is my report for the 2010 Haiti earthquake (see more about the tectonics of this region of the world).
https://earthquake.usgs.gov/earthquakes/eventpage/us6000f65h/executive
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 1921-2021 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.
- in the lower right corner is a small scale plate tectonic map.
- Above that map is a plot showing the USGS finite fault slip model. This shows the location of the fault and color represents how much the fault slipped during the earthquake.
- In the upper right corner is a map that compares the USGS earthquake intensity models (the contoured lines) with the USGS Did You Feel It? observations from real people.
- In the lower center is a map that shows the aftershocks from the M 7.2 earthquake and from the 2010 M 7.0 earthquake.
- In the upper left are two maps that show models of earthquake triggered landslides and earthquake induced liquefaction for this M 7.2 event. Read more about these models here.
I include some inset figures.
Earthquake Aftershocks
Potential for Ground Failure
- 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).
- 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.
- Below are maps showing a comparison between the USGS modeled earthquake triggered landslides and liquefaction potential with the Centre Nationale De Information Géospatiale (CNIGS) probabilistic models of ground failure.
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.
- 2016.01.17 1900-2016 Summary northern Caribbean
- 2021.08.14 M 7.2 Haiti
- 2020.01.28 M 7.7 Cayman Islands
- 2020.01.07 M 6.4 Puerto Rico
- 2019.09.24 M 6.0 Puerto Rico (Mona Passage) Poster
- 2018.08.21 M 7.3 Venezuela
- 2018.01.10 M 7.6 Cayman Trough
- 2016.01.17 M 5.1 pair Cuba
- 2010.01.12 M 7.0 Haiti
Caribbean
General Overview
Earthquake Reports
Social Media
My original Tweet:
#EarthquakeReport for M7.2 #TremblementDeTerre #Terrremoto #Earthquake in #Haiti #HaitiEarthquake #HaitiEarthquake2021
updated poster: compare shaking intensity MMI and aftershock regions between 2010 M 7.0 & 2021 M 7.2
read more about 2010 M 7 Event https://t.co/KDzf1PtjyE pic.twitter.com/wIURgKsbOa
— Jason "Jay" R. Patton (@patton_cascadia) August 15, 2021
Haiti's 1860 Jour de Pâques earthquakes may have released strain in key fault zone https://t.co/JKBJiHZ5jo #RSESpapers Stacey Martin & Susan Hough https://t.co/hz1uosClX3 pic.twitter.com/n2N6nblQui
— ANU Earth Sciences 🌏 (@anuearthscience) July 14, 2022
Given the larger magnitude and farther west location of this 2021 Haiti quake relative to the 2010 earthquake, it is also worth noting the short time elapsed between the last historical sequence of large quakes on this fault. Fig from our 2012 paperhttps://t.co/zLQ8wSbtWr pic.twitter.com/ux17G6bz2F
— Austin Elliott (@TTremblingEarth) August 14, 2021
Why was there a gap between the 2010 and 2021 Haiti earthquakes? Because a sequence of moderate quakes in 1860 released strain in the gap! https://t.co/rpuXfEw78G
— Dr. Susan Hough 🦖 (@SeismoSue) July 15, 2022
I was excited to see & have a chance to comment on a study published in Science yesterday, discussed here. The response to the 2021 Nippes, Haiti, earthquake was very different from the response in 2010, 1/https://t.co/y6l3jjsAYQ
— Dr. Susan Hough 🦖 (@SeismoSue) March 11, 2022
Saturday's M7.2 earthquake in Haiti was close to the 2010 M7.0 earthquake. Both events are devastating on their own but compounded by ongoing problems the region faces. Compare @IRIS_EPO's Teachable Moments:
2010 M7.0: https://t.co/FgYVeGH6Zy
2021 M7.2: https://t.co/z007x1QxC4 pic.twitter.com/VpkCSo90G2
— Southern California Earthquake Center (@SCEC) August 16, 2021
Here is a comparison of Peak Ground Acceleration (perceived shaking) for the January 2010 M7.0 and August 2021 M7.2* events. Note the notable difference at Port-au-Prince. #Haiti #Earthquake
*ShakeMap (version 5) remains preliminary and subject to USGS updates. pic.twitter.com/AiH2FU1NeU
— Steve Bowen (@SteveBowenWx) August 14, 2021
- 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
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
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Contrary to what some people spread around on the internets (some of them major earthquake experts), strike-slip earthquakes can and do generate tsunami (just like this one). More on this below. This M 7.7 earthquake happened along the Oriente fault, which is the Septentrional fault further to the east. This fault is one of the boundaries between the North America plate to the north and the Caribbean plate to the south in a region called the Greater Antilles.
Seismotectonic setting of the Caribbean region. Black lines show the major active plate boundary faults. Colored circles are precisely relocated seismicity [1960–2008, Engdahl et al., 1998] color coded as a function of depth. Earthquake focal mechanism are from the Global CMT Catalog (1976–2014) [Ekstrom et al., 2012], thrust focal mechanisms are shown in blue, others in red. H = Haiti, DR = Dominican Republic, MCS = mid-Cayman spreading center, WP = Windward Passage, EPGF = Enriquillo Plaintain Garden fault.
Plate tectonic configuration of the Caribbean region showing the location of the study cases presented in this issue (numbers refer to papers, arranged as in the issue), and other important geological features of the region (compiled from several sources).
A. Tectonic map of Cayman trough region showing strike-slip faults (heavy lines), oceanic crust (gray) in Cayman trough, and magnetic anomaly identifications (numbered bars) (after Rosencrantz et a., 1988). Arrows show relative displacement directions. Fault zones: OFZ – Oriente; DFZ- Dunvale; EPGFZ – Enriquillo-Plantain Garden; WFZ – Walton; SIFZ – Swan Islands; MFZ – Motagua. Bl. Late Miocene reconstruction of Cayman trough. C. Early Miocene reconstruction.
Bathymetry of central Cayman Trough adapted from Jacobs et al. (1989). Contour interval: 250 m. Dotted line: location of gravity transect.
#EarthquakeReport for the M7.7 left-lateral strike-slip #Earthquake #Terremoto #TremblementDeTerre along the Oriente-Septentrional fault system in the #GreaterAntilles affecting #Cuba #CaymanIslands #Jamaica #tsunami observed and #GroundShaking report:https://t.co/8sTAMIQlq6 pic.twitter.com/Y2PCHHxuDj — Jason "Jay" R. Patton (@patton_cascadia) January 29, 2020 Watch the M7.7 Caribbean earthquake waves roll across the USArray Transportable Array seismic network (https://t.co/RIcNz4bgWq )! #earthquake #JamaicaEarthquake pic.twitter.com/aVSu6B1DTw — IRIS Earthquake Sci (@IRIS_EPO) January 29, 2020 7.7 magnitude earthquake 80 miles ESE of Cayman Brac & Little Cayman#earthquake video is damage from Grand Cayman in the George Town Hospital staff parking lot @lookner pic.twitter.com/AWe3MtFUUB — Raymond Gayle (@Kentsville) January 28, 2020 S-Waves arrive after P-Waves — RIP Beer but a good lesson in earthquake physics. https://t.co/YneCbBEwQd — Switzer Coastal lab (@CoastalLabNTU) January 29, 2020 I've updated the seismicity map with aftershocks of today's M7.7 earthquake in Caribbean in purple. All are to West of mainshock epicenter & most clustered at about 200 km, suggesting rupture propagated to West & has length of ~200 km (expected for M7.7). pic.twitter.com/Ee2NTFOR0Z — Jascha Polet (@CPPGeophysics) January 29, 2020 M 7.7 – 125km NNW of Lucea, Jamaica — Alan Kafka (@Weston_Quakes) January 29, 2020 Here is the IRIS interpreted version of their similar section for reference: https://t.co/byjiAkbhLI — Mark Vanstone (@wmvanstone) January 28, 2020 Jamaica had some tremors 🥴 pic.twitter.com/pubHU8ULHT — kendrabradia (@kendrabradia) January 28, 2020 There was just a 7.3 magnitude earth quake in Jamaica. In my apt in Miami – this just happened. Could feel the whole building swaying. Crazy! pic.twitter.com/r5pPJzcLvm — Nunya Bizniz (@Pladizow) January 28, 2020 More sinkholes appear in towns in Jamaica after a 7.7 magnitude earthquake strikes off the coast of Cuba and Jamaica. pic.twitter.com/b2yaVOHkMp — 🗞️🇻🇮 State of the Territory News (@sottvi) January 28, 2020 #EarthquakeUpdate Tsunami Map showing areas of Jamaica that could be impacted by waves (in yellow) not exceeding 3 feet pic.twitter.com/WeLZUGhGTZ — ODPEM (@odpem) January 28, 2020 It’s getting really wild out there in Jamaica 😐 #earthquake #jamaica pic.twitter.com/X82CyHCBA2 — kendrabradia (@kendrabradia) January 28, 2020 The tanks are part of the Cayman Water West Bay facility.https://t.co/MTioQQPKxI pic.twitter.com/cCruNnS1e5 — bbdd333 (@bbdd333) January 29, 2020 The direction a fault ruptures in an earthquake can affect the intensity of shaking. Using methods like back-projection and finite fault modeling (FFM) helps determine this directivity. https://t.co/LjR89f2p1q — Dr. Kasey Aderhold (@kaseyaderhold) January 28, 2020 Mw=7.8, CUBA REGION (Depth: 27 km), 2020/01/28 19:10:25 UTC – Full details here: https://t.co/NLpq1TBmAc pic.twitter.com/tU0JMJB6Eg — Earthquakes (@geoscope_ipgp) January 28, 2020 On the Oriente fault, 1962 and 1917 #earthquakes are the strongest events before the network set-up, resp. M6.1 and M7. From Van Dusen and Doser, 2000 https://t.co/iy8OnA9r8Z pic.twitter.com/YG8woSpENn — Stéphane Baize (@stef92320) January 28, 2020 Earthquake my family in Cayman Islands pic.twitter.com/Vh8njK0SRs — Jeannine Brown (@Jeannin54070867) January 28, 2020 Mw7.7 #earthquake #Cuba Region #Jamaica #CaymanIslands@QuakeEarly Mwpd magnitude indicated Mw7.8 only 6min after origin time. Mwpd is a rapid size estimate for very large and very long duration earthquakes; for tsunami warning.https://t.co/IjO3uk81xJhttps://t.co/INpfQ6nPJa pic.twitter.com/twnPxiZrkC — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) January 29, 2020 Let's talk about earthquake shaking. Ppl who feel earthquakes sometimes talk about "rollers" versus "shakers." The shaking you feel in any earthquake depends to some extent on geology: if you live in a valley, you tend to feel waves sloshing, or rolling. — Susan Hough (@SeismoSue) January 29, 2020 Looks as if there was a tiny little #tsunami (few centimetres) caused by the M7.7 #earthquake in the #Caribbean yesterday. Gauge data from https://t.co/GfWqeHMv4r pic.twitter.com/Z4FMh8iSxq — Christoph Gruetzner (@ch_gruetze) January 29, 2020 — Jason "Jay" R. Patton (@patton_cascadia) February 1, 2020
Welcome to the next decade of the 21st century. We may look back a decade to review the second most deadly earthquake in the 21st century, from the magnitude M 7.0 Haiti Earthquake on 12 Jan 2010. I put together an overview of this event sequence here. The latest aftershock forecast was tweeted here. I hope people follow this link to stay up to date on these forecasts. Aftershocks have continued in #PuertoRico, with 144 magnitude 3.0 and greater aftershocks recorded since the M6.4 quake on Jan 7. Current models estimate about an 11% chance for future aftershocks of M6.0 or greater. Daily updates can be found at: https://t.co/WFthaXL9vp — USGS (@USGS) January 12, 2020
In so-called ‘earthquake swarms’, numerous earthquakes occur locally over an extended period without a clear sequence of foreshocks, main quakes and aftershocks. The Swiss Seismological Service (SED) registers several of earthquakes swarms every year. They are therefore nothing extraordinary. Swarms usually end after a few days or months. Only seldom does the strength and number of earthquakes increase over time or do occur single, damaging events. How an earthquake swarm develops over time is just as difficult to predict as earthquakes are in general.
Many earthquake swarms occur in regions with complex contiguous fracture systems. The theory is that they are related to the movement of fluid gases and liquids in the Earth’s crust.
Seismotectonic setting of the Caribbean region. Black lines show the major active plate boundary faults. Colored circles are precisely relocated seismicity [1960–2008, Engdahl et al., 1998] color coded as a function of depth. Earthquake focal mechanism are from the Global CMT Catalog (1976–2014) [Ekstrom et al., 2012], thrust focal mechanisms are shown in blue, others in red. H = Haiti, DR = Dominican Republic, MCS = mid-Cayman spreading center, WP = Windward Passage, EPGF = Enriquillo Plaintain Garden fault
Seismicity and kinematics of the NE Caribbean. The inset shows Caribbean and surrounding plates, red arrows show relative motions in cm/yr: a: NEIC seismicity 1974–2015 is shown with circles colored as a function of depth, stars show large (M > 7) instrumental and historical earthquakes; b: red and blue bars show earthquake slip vector directions derived from the gCMT database [www.globalcmt.org], black arrows show the present-day relative motion of the NA plate with respect to the Caribbean.
Contoured bathymetry map of the northeastern Caribbean showing a summarized tectonic setting. Isobaths based on satellite-derived bathymetry gridded at 1 arcminute intervals (Smith and Sandwell, 1997) using the free software Generic Mapping Tools (GMT; Wessel and Smith, 1998). The purple dashed rectangle marks the study area. Thick green arrows show the relative convergence motion between the North American and the Caribbean plates. GPS-derived velocities with respect to the North American plate are shown with thin red arrows, the arrow length being proportional to the displacement rate (Manaker et al., 2008). Error ellipse for each vector represents two-dimensional error, 95% confidence limit. The thick blue dashed line marks the Hispaniola-PRVI block boundary as suggested by ten Brink and Lopez-Venegas (2012). The green area shows the extension of the Muertos thrust belt (Granja Bru~na et al., 2009, 2014, this study). NOAM ¼ North American. CARIB ¼ Caribbean. EPGFZ ¼ Enriquillo-Plantain Garden fault zone. SFZ ¼ Septentrional fault zone. BF ¼ Bunce fault. SB ¼ Sombrero basin. PRVI BLOCK ¼ Puerto RicoeVirgin Islands block. VIB ¼ Virgin Islands basin. MR ¼ Mona rift. IFZ ¼ Investigator fault zone. JS ¼ Jaguey spur. SCR ¼ St. Croix rise. SCI ¼ St. Croix Island. The inset map shows GPS-derived velocities with respect to St. Croix Island (SCI), the arrow length being proportional to the displacement rate (ten Brink and Lopez-Venegas, 2012). Error ellipse for each vector represents two-dimensional error, 95% confidence limit. MI ¼ Mona Island. CI ¼ Culebra Island. STI ¼ St. Thomas Island. AI ¼ Anegada Island. SCI ¼ St. Croix Island. IFZ ¼ Investigator fault zone.
Map of Puerto Rico showing known and possible Quaternary-active faults. Well-located faults are shown by solid lines; inferred fault locations are shown by dashed lines. The northwest end of the Great Southern Puerto Rico fault zone (GSPRFZ) likely follows the Cerro Goden fault, but an alternative location shown by Jansma et al. (2000) and Jansma and Mattioli (2005) is indicated by the dashed lines. The GSPRFZ is shown by double lines because the fault zone mapped in bedrock is up to 2 km wide. Map base is a digital elevation model (DEM) created from 30-m (∼1 arcsec) National Elevation Dataset (NED) (see Data and Resources). Bathymetric contours are from ten Brink et al. (2004).
Regional morphotectonic interpretation. Faults picked from the seismic data and correlated along strike with the aid of swath bathymetry data. Thick orange lines mark the major onshore structures (GSPRFZ ¼ Great Southern Puerto Rico fault zone; LVF ¼ Lajas Valley fault). Thin orange lines show the faults mapped by Bawiec (1999). FC ¼ Frederickted canyon. WIFZ ¼ Western sector of the Investigator fault zone. CIFZ ¼ Central sector of the Investigator fault zone. EIFZ ¼ Eastern sector of the Investigator fault zone. PF ¼ Ponce fault. BTF ¼ Bajo Tasmanian fault. CMF ¼ Caja de Muertos fault. CF ¼ Central fault. MPC ¼ Mona passage canyon. R ¼ Recess. S ¼ Salient in the deformation front. Ss ¼ Salient in the deformation front referred in Section 4.1. JP ¼ Jungfern passage. WC ¼ Whiting canyon. VC ¼ Vieques canyon. Z ¼ Bench in the northern flank of St. Croix rise. PRSBF ¼ Puerto Rican sub-basin fault. RR ¼ Relay ramp.W¼ Canyon referred to in Section 4.4.3. Q ¼ 080-oriented fault in Section 4.4.3. T ¼ possible source of the 1867 earthquake (Barkan and ten Brink, 2010) referred in Section 5.2.
(top) GPS velocities used in the model shown with respect to the North American plate defined by the velocity of 25 GPS sites located in the stable interior of the plate [Calais et al., 2006]. (bottom) GPS velocities shown with respect to the Caribbean plate as defined in the best fit block model described in the text. Error ellipses are 95% confidence. Blue arrows show GPS velocities from Pérez et al. [2001] in Venezuela because of their large uncertainty and the lack of common sites with our solution, which prevents us from rigorously combining them to our solution. They are not used in the model but used to show that they are consistent with the rest of the velocity field.
Earthquake focal mechanisms [Ekstrom et al., 2012] and locations [Engdahl et al., 1998] along the subduction interface and cross sections showing with a thick black line the position of the Caribbean-North America plate interface used in the model. Other faults are shown with thick dashed black lines. SF = Septentrional fault, PRT = Puerto Rico trench, MT = Muertos trench, LAT = Lesser Antilles trench, NHT = Northern Hispaniola trench. White dots on the map (top) show the vertices of the triangles used to discretize the subduction interface. Grey lines on cross section show the bathymetry with significant vertical exaggeration compared to the earthquake depth scale. The area used for each cross
Hypothesized model of the tectonic relationships. The PRVI sits between two subducting slabs; the dip angles of the two subducting slabs increase from east to west. The North American Plate splits in the eastern PRVI (modified after ten Brink, 2005). North arrow is black. Red arrows show the directions of movement for the PRVI and Hispaniola microplate with respect to the North American Plate. The light grey area at the centre is above 2 km bathymetry line. PRVI, Puerto Rico Virgin Islands; AP, Anegada Passage
Sections across the Lesser and Greater Antilles subduction showing topography (grey line), earthquake hypocenter [Engdahl et al., 1998], velocity magnitude at the GPS sites (red circles with 95% confidence error bar), velocity predicted by the best fit model (solid red line), and velocity predicted by a forward model where we impose full coupling on the subduction interface (dashed blue line). The misfit of the data to a fully locked plate interface is apparent on the three Lesser Antilles cross sections.
Velocities at selected GPS sites in the NE Caribbean shown with respect to the Caribbean plate (a) and to the North American plate (b). Error ellipses are 95% confidence.
Block geometry used in the models tested. Solid black lines show the block boundaries for the best fit model, thick dashed lines show other tested block boundaries. NHIS = North Hispaniola, PRVI = Puerto Rico and Virgin Islands, GONA = Gonave, HISP = Hispaniola, NLAB = North Lesser Antilles Block, SJAM = South Jamaica. CARW = Caribbean West, CARE = Caribbean East, NVEN = North Venezuela, MARA = Maracaibo, ANDE = Andes, HFBT = Hispaniola fault and thrust belt, NMF = Neiba-Matheux thrust, SJF = South Jamaica fault. Thin dashed lines are depth contours of the subduction interface used in the model, derived from the earthquake hypocenters cross sections shown in Figure 4.
Coupling ratio estimated along the Greater-Lesser Antilles subduction interface estimated on the discretized plate interface also shown in Figure 4. Residual velocities are shown with black arrows. We omitted their error ellipses for a sake of readability. The thin dashed line indicates the boundary of the Bahamas Platform. Note the coincidence between the transition from coupled to uncoupled plate interface with the transition from Bahamas Platform collision to oceanic subduction at the Puerto Rico trench.
Fault slip rates and slip rate deficit from the best-fit model. Open circles represent the surface projection of fault nodes. Heavy black lines show the model block boundaries. Vertical faults are shown to the right of each main figure. (a) Fault slip rates (mm yr−1). (b) Slip rate deficit (mm yr−1).
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. #EarthquakeReport for (so far) the mainshock M6.4 #Earthquake in #PuertoRico #PuertoRicoEarthquake #terremoto #TremblementDeTerre #temblor minor #tsunami 5cm at Magueyes Island tide gagehttps://t.co/J5jfn8LJWvhttps://t.co/Vh4RcbVMCN EQ history here https://t.co/eH5gBgIkYT pic.twitter.com/CXuTjdDU1y — Jason "Jay" R. Patton (@patton_cascadia) January 7, 2020 "In so-called 'earthquake swarms', numerous earthquakes occur locally over an extended period without a clear sequence of foreshocks, main quakes and aftershocks", from @seismoCH_E: https://t.co/wZqNJd1YFS pic.twitter.com/qBXfB0TQ1i — Dr. Kasey Aderhold (@kaseyaderhold) January 11, 2020 Puerto Rico has been hit by spate of damaging M5-6 earthquakes over the past few days. All this shaking is due to Puerto Rico’s location along the edge of the Caribbean plate. This adds to the damage still present from Hurricane Maria: https://t.co/cQ82kTD7g0 @DiscoverMag pic.twitter.com/v2fTav0oYe — Dr. Erik Klemetti (@eruptionsblog) January 7, 2020 Animation from the Interactive Earthquake Browser showing #earthquakes near #PuertoRico between Nov 1, 2019 and Jan 7, 2020 (8 am). The color of the dots indicates the depth (purple means shallow) and the size of the dot indicates the magnitude. https://t.co/Gs3ykBEp0y pic.twitter.com/EBzkXgzumD — IRIS Earthquake Sci (@IRIS_EPO) January 7, 2020 Auto solution FMNEAR (Géoazur/OCA) with regional records for the 2020-01-07 08:24:26 UTC M6.5 PUERTO RICO 17.87N 66.79W 10km depth (Loc EMSC used to trigger inversion).https://t.co/UHDsc1hVXA (not on mobile version) — Bertrand Delouis (@BertrandDelouis) January 7, 2020 Backprojection of the M6.4 #PuertoRicoEarthquake pic.twitter.com/FaACUzK9ks — IRIS Earthquake Sci (@IRIS_EPO) January 7, 2020 The movie. Perspective view from SE rotating to NE. Swarm seismicity suggests steeply NNE dipping structures above ~12km, and deeper, N-S & WNW-ESE vertical faulting within a gently N dipping structure which continue northwards under Puerto Rico at base of background seismicity. pic.twitter.com/a3sA5C5JF2 — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) January 12, 2020 NASA JPL image release of displacement map for Puerto Rico earthquake, from #InSAR processing of Copernicus Sentinel-1 data. https://t.co/wEJQ8tQ4dm@NASAJPL pic.twitter.com/dVURwkBawQ — Eric Fielding (@EricFielding) January 11, 2020 PR is more used to dealing with hurricanes than earthquakes. Due of this, housing is mostly concrete and worse, elevated on piers (carports/flooding). Both aspects make them more vulnerable to EQs. These pics are from a few days ago from smaller eqs on PR #PuertoRicoEarthquake pic.twitter.com/IXRdP0mBNP — Forrest Lanning (@rabidmarmot) January 7, 2020 #EarthquakeReport Shaking Intensity from @USGSBigQuakes for M 6.4 #Earthquake in #PuertoRico #PuertoRicoEarthquake #Terremoto #TremblementDeTerre #Temblor #TemblorPuertoRico #TemblorPR #TemblorEnPuertoRico pic.twitter.com/RfJpjoUVmF — Jason "Jay" R. Patton (@patton_cascadia) January 7, 2020 — Jason "Jay" R. Patton (@patton_cascadia) January 7, 2020 Dozens of earthquakes, some as large as M5-6, have struck the southern coast of Puerto Rico over the past few days. After Hurricane Maria, these quakes add to the challenge of recovery on the Carribbean island (Image: USGS) https://t.co/cQ82kTUIEA @DiscoverMag pic.twitter.com/zFPcAN77We — Dr. Erik Klemetti (@eruptionsblog) January 7, 2020 No todos los heroes tienen capa pic.twitter.com/07WqFgXeh6 — htj (@htjlaw) January 7, 2020 Seismo Blog: Deadly Earthquakes in the Muertos Trough — Berkeley Seismo Lab (@BerkeleySeismo) January 7, 2020 Watch the waves from the M6.4 #PuertoRicoEarthquake roll across the USArray Transportable Array seismic network (https://t.co/RIcNz4sRNY )! pic.twitter.com/0bWbX3SgTS — IRIS Earthquake Sci (@IRIS_EPO) January 7, 2020 #PuertoRico 🇵🇷 en estado de emergencia, tras los fuertes sismos de hoy. — Geól. Sergio Almazán (@chematierra) January 7, 2020 Central Meteorológica y Geológica del Caribe pública las siguientes fotos en Facebook de la escuela Agripina Seda en Guanica. pic.twitter.com/y3CkkGuHVV — Nuria Sebazco (@nsebazco) January 7, 2020 https://t.co/ikNyzpw9xJ #TemblorPR #TemblorEnPuertoRico #earthquakes pic.twitter.com/mJT89HqyLl — temblor (@temblor) January 8, 2020 https://t.co/ikNyzpNKph #TemblorPR #TemblorEnPuertoRico #earthquakes pic.twitter.com/867UGoTgcw — temblor (@temblor) January 8, 2020 #EarthquakeReport interpretive poster showing potential for earthquake induced liquefaction from M6.4 #PuertoRicoEarthquake #PuertoRico #EarthquakePR #EarthquakePuertoRico from @USGSBigQuakes modeling here https://t.co/IszgHm9rL4 — Jason "Jay" R. Patton (@patton_cascadia) January 8, 2020 — Jason "Jay" R. Patton (@patton_cascadia) January 8, 2020 A few #landslides triggered by the recent Puerto Rico #earthquake, near the Mw 6.4 epicenter area. #Sentinel2 upscaled image comparison for Dec 29 and Jan 8. Location ~10km east of Guánica, along the southern coast. pic.twitter.com/c0OuhGu3OK — Sotiris Valkaniotis (@SotisValkan) January 8, 2020 Quickly drawn idea. Turns out that the Great Southern Puerto Rico Fault is further east of Ponce, following the Rio Grande de Anasco north of the current sequence – I have found few detailed or helpful fault maps for Puerto Rico, hence my error. pic.twitter.com/bQNYFmF4kT — Jamie Gurney (@UKEQ_Bulletin) January 9, 2020 USGS forecasts a 3 percent chance of one or more aftershocks larger than a magnitude 6.4 in Puerto Rico in the next week and that smaller earthquakes are likely to occur. Forecasts are updated periodically and official information can be found here: https://t.co/YpNeR6rxQd pic.twitter.com/ainSKWbjMU — USGS (@USGS) January 9, 2020 Watching earthquakes roll in on the real time monitor 😮 Video taken by Alena Leeds and Elizabeth Vanacore, two of the folks on the @USGS+@redsismica field crew installing @usgs_seismic stations pic.twitter.com/VFiwtDZY8t — Emily Wolin (@GeoGinger) January 11, 2020 En Puerto Rico, muchos se preguntan ansiosamente ¿y ahora, qué viene? Nadie puede predecir terremotos, pero la sismología puede dar pronósticos: estimar probabilidades de que ocurran más sismos, pequeños o grandes. Lo hace @USGS https://t.co/tVUXGWrqXY Explicación 👇 pic.twitter.com/Uvt7VWJMOK — Pablo Ampuero (@DocTerremoto) January 11, 2020 The GS-PR01 station was the closest to this morning's M5.9, providing valuable strong motion recordings. pic.twitter.com/SgD4FucQCg — USGS_Seismic (@usgs_seismic) January 11, 2020 #EarthquakeReport #Earthquake #Aftershocks in #PuertoRico interpretive posters with mechanisms and comparisons (6.4 v 5.9) intensity and liquefaction susceptibility (6.4 v 5.9)#PuertoRicoEarthquakes #TerremotoPR #TerremotosPR #terremoto #terremotopuertorico #Terremotos pic.twitter.com/YANM7Uze8i — Jason "Jay" R. Patton (@patton_cascadia) January 12, 2020 Time progression of Puerto Rico earthquake sequence based on local network catalog — Jascha Polet (@CPPGeophysics) January 11, 2020 NASA JPL ARIA processing of new Copernicus Sentinel-1 #InSAR for Puerto Rico earthquakes, using data from 2020/01/02–2020/01/14 shows displacement of the land surface. The coast centered on Guayanilla Bay moved 14 cm (5.5 inches) downward in radar line-of-sight. Quakes from USGS pic.twitter.com/iwi69RHuez — Eric Fielding (@EricFielding) January 15, 2020 Update on the Southern #PuertoRico Seismic Sequence since December 27 until January 25th 00:26 am. — Janira Irizarry (@jany_ip) January 25, 2020
This is the ten year commemoration of the 2010 magnitude 7 earthquake in Haiti that caused widespread damage and casualties, triggered thousands of landslides, caused tsunami, triggered a turbidity current, and caused thousands to be internally displaced.
Deaths from earthquakes since 1900. The toll of the Haiti quake is more than twice that of any previous magnitude-7.0 event, and the fourth worst since 1900.
Seismotectonic setting of the Caribbean region. Black lines show the major active plate boundary faults. Colored circles are precisely relocated seismicity [1960–2008, Engdahl et al., 1998] color coded as a function of depth. Earthquake focal mechanism are from the Global CMT Catalog (1976–2014) [Ekstrom et al., 2012], thrust focal mechanisms are shown in blue, others in red. H = Haiti, DR = Dominican Republic, MCS = mid-Cayman spreading center, WP = Windward Passage, EPGF = Enriquillo Plaintain Garden fault.
Hazard maps using grid of VS30 values shown in Figure 7: (top) PGA (%g) with 10% probability of exceedance, (bottom) PGA (%g) with 2% probability of exceedance in 50 years.
Tectonic setting of the northeastern Caribbean and Hispaniola. a, Major active plate-boundary faults (black lines), instrumental seismicity (National Earthquake Information Center database, 1974–present) and Caribbean–North America relative motion (arrow). P.R. Puerto Rico; D.R. Dominican Republic. b, Summary of the present-day tectonic setting of Hispaniola. Estimated historical rupture areas are derived from archives. 1860, 1953 and 1701 are the dates of smaller magnitude, poorly located events. Vertical strike-slip events are shown as lines; dip-slip events are shown as projected surface areas. The red arrows show geodetically inferred long-term slip rates (labelled in mmyr-1) of active faults in the region from the block model discussed here (the arrows show motion of the southern with respect to the northern block).
Tectonic setting and active faulting in Haiti. (a) Major anticlines (lines with arrows, dashed white: growing and grey: older), active thrusts (black), and strike-slip faults (EPGF and SF: in red) from this study [Mann et al., 1995; Pubellier et al., 2000; Mauffret and Leroy, 1997; Granja Bruña et al., 2014]. Blue (1): rigid Beata oceanic crust block. Dark purples: toleitic complex oceanic crust outcrops. Orange: Cul-de-Sac and Enriquillo (CSE) ramp basins; brown (2): Hispaniola volcanic arc. Black crosses: metamorphic Cretaceous basement; yellow: rigid Bahamas bank. Haiti FTB: Haiti fold and thrust belt. Grey line: trench. Double black arrows: regional compression deduced from mean orientations of folds and thrusts. (b) Active faulting in southern Haiti. Topography and bathymetry (contours each 200 m) from Global Multi-Resolution Topography (GMRT) synthesis (http://www.geomapapp.org). Faults, folds, and symbols as in Figure 1a. Simple red and black arrows: strike-slip motion. In orange: push-down troughs of Port-au-Prince Bay and Azuei and Enriquillo Lakes in the CSE ramp basin. Inset (bottom left): fault geometry and kinematics. Grey ellipse: zone with en echelon troughs in N100°E direction. Inset (top right): simplified strain ellipse in southern Haiti.
(a) Active faulting and seismicity in the southeastern part of Haiti. Topography and bathymetry (contours each 100 m), from Advanced Spaceborne Thermal Emission and Reflection (http://asterweb.jpl.nasa.gov/) and Shuttle Radar Topography Mission 30+ (http://www2.jpl.nasa.gov/srtm/), respectively, and the 1:25000 bathymetric chart of the Hydrographic and Oceanographic Department of the French Navy (contours at 2, 5, 10, 20, 30, 50, 100, and 130m) in the Port-au-Prince Bay. Faults, folds, and symbols as in Figure 1. Red star: 2010 main shock epicenter from Mercier de Lépinay et al. [2011] with the centroid moment tensor from Harvard University (http://www.globalcmt.org); seismicity from Douilly et al. [2013], and focal mechanisms from Nettles and Hjörleifsdóttir [2010]. Location of Figure 3a is indicated. PAP, Port-au-Prince. Folds in CSE ramp basin with locations of Figures 4a and 4b are indicated: PaPT: Port-au-Prince thrust; DT: Dumay thrust; NaC: Nan Cadastre thrust (see Figure 4b); Jac: Jacquet thrust; Gan: Ganthier thrust (see figure 4a). Red and white star near DT: location of Figure 4d. (b) NNE-SSW geological cross section across the Cul-de-Sac-Enriquillo plain. Geology from www.bme.gouv.ht and Mann et al. [1991b] (supporting information Figure S5) with colors of units as in Figure 2c. Profile location shown in Figure 2a; topography as in Figure 1. No vertical exaggeration. (c) Three-dimensional block diagram showing the geology, the aftershocks [from Douilly et al., 2013], and the fault system along a N-S cross section (location in Figure 2a). The block highlighted in red is uplifting in between the LT and the EPGF.
(a) Active faulting in the 2010 earthquake epicentral area. Active faults, symbols, topography, and bathymetry as in Figure 2a. Location of Figure 3b is indicated. SSW-NNE topographic profiles are shown in the inset. ΔR: fault throw at the seafloor. Vertical exaggeration (VE): 20X; α: slope of the Léogâne delta fan. (b) The Lamentin thrust in Carrefour. Topography from lidar data (contours at 5m vertical interval). Rivers in blue, with thicker traces for larger ones. Inset in the lower left corner: topographic profile BB′ along of the Lamentin fold crest (VE: 5X). Inset in the upper right corner: topographic profile AA′ perpendicular to the Lamentin thrust system (VE: 2.5X) and the most plausible geometry of the thrusts (with no vertical exaggeration). In yellow: upper Miocene limestone; in grey: Quaternary conglomerates. MT:main thrust. The width of the fold and the slope of the fan surface constrain the rooting depth of the emergent ramp to the décollement [e.g.,Meyer et al., 1998].
Active folding in the Cul-de-Sac-Enriquillo ramp basin. (a) Aerial photograph of the 8 km long Ganthier Quaternary fold. (b) Lidar topography of the Nan Cadastre Quaternary thrust folding. Inset: topographic profile AA′ and possible interpretation at depth. (c) Field photograph along the eastern flank of the Bois Galette River (location in Figure 4a) showing the folded alluvial sediments of the Ganthier fold dipping ~30°N. (d) Field photograph and interpretation of the 50 ± 15° southward dipping Dumay thrusts (in red) exposed in cross section on the eastern bank of the Rivière Grise (location in Figure 2a). The fault offsets by several tens of centimeters Quaternary sediments (lacustrine and conglomerates) incised by the river.
Interseismic GPS velocities. The GPS velocity field is determined from GPS campaigns before the 12 January 2010 earthquake. The ellipses and error bars are 95% confidence. a, Velocities with respect to the North American plate. b, Velocities with respect to the Caribbean plate. c, Velocity profile perpendicular to the plate boundary (coloured circles and one-sigma error bars) and best-fit elastic block model (solid lines). Blue D profile-perpendicular (‘strike-slip’) velocity components; orange D profile-parallel (‘shortening’) velocity components. The profile trace and width are indicated by dashed lines in a and b.
GPS velocities shown with respect to the North American plate (A) and to the Caribbean plate (B). Error ellipses are 95% confidence. (C) North–south profile including GPS sites shown with the dashed box shown on panels A and B. Velocities are projected onto directions parallel (blue) and normal (red) to the EPGF direction. MS = Massif de la Selle, CdS = Cul-de-Sac basin, MN= Matheux-Neiba range, PC= Plateau Central, PN= Plaine du Nord, EF= Enriquillo fault, SF= Septentrional fault.
Top and middle: comparison between the best-fit model (solid lines) and GPS observations for the strike-slip (blue) and shortening (red) components for the one– fault model, i.e. with oblique slip on the south-dipping fault. Bottom: interpretative geological cross-section using information from Saint Fleur et al. (2015). The red line indicates the model fault with its locked portion shown as solid. The surface trace of the fault in the best-fit model coincides with the northern limb of the Ganthier fold, indicated by the letter G. The gradient of GPS velocities coincides with the southern edge of the Cul-de-Sac basin, while the Matheux range appears devoid from present-day strain accumulation. D = Dumay locale where Terrier et al. (2014) report reverse faulting affecting Quaternary sediments. G = Ganthier fold (Mann et al., 1995).
Coseismic displacements from GPS measurements. a, Map of horizontal coseismic displacements. Note the significant component of shortening, similar to the interseismic velocity field (Fig. 2). The orange arrows have been shortened by 50% to fit within the map. Displacements at stations TROU and DFRT, cited in the text, are labelled. NR Can Natural
Deformation observations and rupture model. a, Interferogram (descending track, constructed from images acquired on 9 March 2009 and 25 January 2010), GPS observed (black) and model (red) coseismic displacements. The yellow circles show aftershocks. G D Greissier, L D Léogâne, PaP D Port-au-Prince. EF D Enriquillo–Plantain Garden fault. The black rectangle shows the surface projection of the modelled rupture; the black–white dashed line is the intersection with the surface. LOS displ:D line-of-sight displacement. b, Total slip distribution from a joint inversion of InSAR and GPS data, viewed from the northwest. c, Interpretative cross-section between points A and B indicated on a. The red line shows coseismic rupture.
Cross sections perpendicular to the Enriquillo fault illustrating possible fault structures. Hypocenters within the rectangular boxes are included in the corresponding cross section. The open triangles in the cross sections indicate the surface trace of the Enriquillo fault. The red line shows the main earthquake rupture on the Léogâne fault; blue lines show the Trois Baies thrust fault; green lines show south-dipping antithetic structures delineated by aftershocks possibly triggered by Coulomb stress changes following the mainshock. The black lines in the cross sections show the hypothesized location of the Enriquillo fault, which is believed to dip from 65° north (Prentice et al., 2010) to vertical.
Coulomb stress changes imparted by the January 12, 2010, Mw=7.0 rupture resolved on surrounding faults inferred from Mann and others (2002). Thrust faults dip 45°.
Coulomb stress changes imparted by the January 12, 2010, Mw=7.0 rupture to the Septentrional Fault, assuming a friction of 0.4 (a friction of 0.0 yields a similar result, with the peak stress shifted 25 km to the west). Stress changes are positive but very small. The two 1/26/10 aftershocks are the only events thus far to locate well off the source model; if they are left-lateral events on roughly E-W planes, then they would have been promoted by stress imparted by the January 12 mainshock rupture.
Newstatic slipmodel for the 2010 Haiti earthquake and induced Coulomb stress changes. (a) Axonometric view from SE showing the slip distribution on two faults (EPGF and LT) determined by modeling geodetic data (GPS and interferometry) and coastal uplift values recorded by coral (see supporting information). Arrows (white for EPGF and black for LT) indicate the motion of the hanging wall with respect to the footwall. Land surfaces in grey. Red lines: active faults. Blue bars: coastal uplift measured by using corals from Hayes et al. [2010]. Red bars: uplift predicted by our model. Focal mechanisms indicated the EPGF (dark yellow) and Lamentin fault (green) geometry. (b) Coulomb stress changes induced by the slip model we determined, in map view at 7.5 km depth. Black rectangles: modeled faults. Epicentral locations of aftershocks from Douilly et al. [2013]. Insets in the upper left corners: parameters of the receiver faults used for the Coulomb stress calculation. Calculated for receiver faults having the same geometry as the strike-slip EPGF (dark yellow lines) and as the Lamentin thrust (dark green lines), respectively (Figure 5b, left and right).
Calculated coseismic Coulomb stress change on the regional faults of southern Haiti based on coseismic slip associated with our preferred model (Fig. 5c) and two assumptions of apparent friction. The Enriquillo fault is assumed to dip 65° to the south with a rake of 20°. The Trois Baies fault is assumed to dip 55° to the north with a rake of 70°. All other faults are assumed to dip at 60° and a rake of 90° (pure
Overview of population movements. (A) Shows the geography of Haiti, with distances from PaP marked. The epicenter of the earthquake is marked by a cross. (B) Gives the proportion of individuals who traveled more than d km between day t − 1 and t. Distances are calculated by comparing the person’s current location with his or her latest observed location. In (C), we graph the change in the number of individuals in the various provinces in Haiti. (D) Gives a cumulative probability distribution of the daily travel distances d for people in PaP at the time of the earthquake. (E) Shows the cumulative probability distribution of d for people outside PaP at the time of the earthquake. Finally, (F) gives the exponent α of the power-law dependence of d—the probability of d is proportional to d−α. These are obtained by a maximum-likelihood method (33), and differ from the slopes of the lines in (D) and (E) by unity since these are the cumulative distributions.
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.
Tectonic setting and landslide distribution map of the study area. (a) Area surrounding the Mw 7.0 January 2010 Haiti earthquake epicenter; beach ball shows focal mechanism (earthquake.usgs.gov). (b) Tectonic setting of the Caribbean plate boundaries. Red star and the points are locations of main shock and major aftershock distributions, respectively. (c) Topographic setting and mean local relief (white circles with±1σ whiskers) of pre- and post-earthquake landslides: alluvial plains and fans (APF), coastal cliff (CSC), deeply incised valley (DIV), dissected hilly and mountainous terrain (HDHM), round crested slopes and hills (RLH), moderately steep slopes (MR), plateau escarpments (PE), and steep faulted hills (SFH).
Distribution of (a) coseismic and (b) aseismic landslides along a reach of the Momance River, Haiti; black star is location of 2010 earthquake epicenter; white arrow is flow direction. Old landslides may likely be of prehistoric origin.
Regional distribution of co- and aseismic landslides, and re-activated slope failures. (a) Normalized spatial density of pre-earthquake aseismic landslides within 1-km radius (see text). (b) Spatial density of coseismic landslides. (c) Spatial density of re-activated landslides. (d and e) Fraction of area affected by (d) aseismic and (e) coseismic
Distribution of coseismic deformation, slip, and landslide density. (a) Vertical-deformation signal from InSAR (after Hayes et al., 2010); black circles are mapped coseismic landslides; the black star is the epicenter. (b) Normalized landslide density map (cf. Fig. 4). (c) Rupture model and coseismic slip amplitudes from inversion of InSAR data, field based off-set measurements, and broadband teleseismic body-waveform data (after Hayes et al., 2010). (d) Block diagram of the Léogâne thrust and Enriquillo–Plantain Garden Fault blind rupture. Normalized landslide density superimposed on data by Mercier de Lépinay et al. (2011). Inset block diagram shows proposed fault geometry by Hayes et al., (2010) for Haiti earthquake ruptures. Thick solid lines are surface projections of each fault; PaP: Port-au-Prince.
Along-strike (W–E) distribution of (a) mean coseismic deformation (Hayes et al., 2010), (b) coseismic and re-activated normalized landslide density, (c) mean local relief, and (d)mean hillslope gradient in the uplifted section.N–S distribution of (e) mean coseismic deformation (Hayes et al., 2010), (f) coseismic and re-activated landslide density, (g)mean local relief, and (h) mean hillslope gradient in both uplifted and subsided parts. Inset maps show locations of the swaths. Black lines (c, d, g and h) and shadings are means and±1 σ in 60-m bins. Light and dark grey boxes delimit peaks in normalized landslide density (b), and sub-sections of differing dominant fault geometries in (e). Dashed grey lines are regional means; scale differs between panels (b and f) in coseismic and re-activated landslide density.
Summary of coseismic landslide inventory data from documented reverse or thrust-fault earthquakes. Left panel shows extent of faulting recorded in historical (grey bars) and recent earthquakes (black bars; modified after McCalpin, 2009). Thick and thin black bars are lengths of surface and blind fault ruptures; estimates of surface rupture lengths (grey bars) and maximum coseismic uplift (light grey arrows) from Wells and Coppersmith (1994); lower limits from Bonilla (1988). Maximum coseismic uplift (MCU, dark grey arrows) and surface/blind ruptures: (1)Wenchuan, China, Mw 7.9 (Liu-Zeng et al., 2009); (2) Chi-Chi, Taiwan, Mw 7.6 (Chen et al., 2003); (3) Haiti Mw 7.0 (Hayes et al., 2010); (4) Iwate-Miyagi, Japan, Mw 6.9 (Ohta et al., 2008); (5) Northridge, USA, Mw 6.7 (Shen et al., 1996); and (6) Lorca, Spain, Mw 5.2 (Martinez-Diaz et al., 2012). Right panel shows hanging wall and foot-wall areas affected by coseismic landsliding, and box-and-whisker plots of local relief. Box delimits lower and upper quartiles and median; whiskers are 5th and 95th percentiles; open circles are outliers. Landslide inventory data from Gorum et al. (2011), Liao and Lee (2000), Yagi et al. (2009), Harp and Jibson (1995), and Alfaro et al. (2012); landslide lower limits are from Keefer (1984).
A: Bulk density, magnetic suscep- GC-2 tibility, 234Th (dpm/g), and photo of GC2 recovered from Canal du Sud at 1753 m. The 12 January turbidite contains 5-cm-thick basal bed of black sand and 50 cm of mud above, forming turbidite-homogenite unit. Bulk density decreases upward to nearly seawater values, and magnetic susceptibility signal is higher near base, corresponding to sand rich in magnetic minerals analyzed at 55, 113, and 143 cm (plag—plagioclase; qtz—quartz). Boxes delineate 12 January and older events.
A: Semitransparent lens on Chirp profile is 12 January earthquake-generated turbidite. B: CTD (conductivity, temperature, depth) transmissometer measurements of water column obtained at 1750 m. Anomaly in beam attenuation in lower 600 m is interpreted as sediment plume that has remained in suspension since 12 January.
Tsunami flow depths and runup heights measured along coastlines in the Gulf of Gonaˆve and along Hispaniola’s south coast.
This morning (my time) there was a moderately deep earthquake along the coast of southern Mexico and northern Guatemala. Here is my Temblor article about this M=6.6 earthquake and how it might relate to the 2017 M=8.2 quake. 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 ≥ 6.5 in one version. There are also some interesting relations between different historic earthquakes.
A. Geodynamic and tectonic setting alongMiddle America Subduction Zone. JB: Jalisco Block; Ch. Rift—Chapala rift; Co. rift—Colima rift; EGG—El Gordo Graben; EPR: East Pacific Rise; MCVA: Modern Chiapanecan Volcanic Arc; PMFS: Polochic–Motagua Fault System; CR—Cocos Ridge. Themain Quaternary volcanic centers of the TransMexican Volcanic Belt (TMVB) and the Central American Volcanic Arc (CAVA) are shown as blue and red dots, respectively. B. 3-D view of the Pacific, Rivera and Cocos plates’ bathymetrywith geometry of the subducted slab and contours of the depth to theWadati–Benioff zone (every 20 km). Grey arrows are vectors of the present plate convergence along theMAT. The red layer beneath the subducting plate represents the sub-slab asthenosphere.
Kinematic model (mantle reference frame) of the subducting Cocos slab along the MAT in the vicinity of Cocos–Caribbe–North America triple junction since Early Miocene. The evolution of Caribbean–North America tectonic contact is based on the model of Witt et al. (2012). The blue strips represent markers on the Cocos plate. Note how trench roll forward is associated with steep slab in Central America, whereas trench roll back is associated with flat slab in Mexico.
Present setting of Central America showing plates, Cocos crust produced at East Pacifi c Rise (EPR), and Cocos-Nazca spreading center (CNS), triple-junction trace (heavy dotted line), volcanoes (open triangles), Middle America Trench (MAT), and rates of relative plate motion (DeMets et al., 2000; DeMets, 2001). East Pacifi c Rise half spreading rates from Wilson (1996) and Barckhausen et al. (2001). Lines 1, 2, and 3 are locations of topographic and tomographic profi les in Figure 6.
(A) Tomographic slices of the P-wave velocity of the mantle at depths of 100, 300, and 500 km beneath Central America. (B) Upper panels show cross sections of topography and bathymetry. Lower panels: tomographic profi les showing Cocos slab detached below northern Central America, upper Cocos slab continuous with subducted plate at Middle America Trench (MAT), and slab gap between 200 and 500 km. Shading indicates anomalies in seismic wave speed as a ±0.8% deviation from average mantle velocities. Darker shading indicates colder, subducted slab material of Cocos plate. Circles are earthquake hypocenters. Grid sizes on profi les correspond to quantity of ray-path data within that cell of model; smaller boxes indicate regions of increased data density. CT—Cayman trough; SL—sea level (modifi ed from Rogers et al., 2002).
Proposed model of faults kinematics and coupling along the Cocos slab interface, revised from Lyon-Caen et al. (2006). Numbers are velocities relative to CA plate in mmyr−1. Focal mechanisms are for crustal earthquakes (depth ≤30 km) since 1976, from CMT Harvard catalogue.
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.
“When a fault slips during an #earthquake, there are changes in stress in the surrounding crust. These changes can either promote or inhibit the subsequent earthquake, depending on the orientation and type of fault on which the stress is imparted.” https://t.co/Qj4iOTQLwR — Dr Lucy Jones Center (@DLJCSS) February 3, 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.
Busy week! 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). https://earthquake.usgs.gov/earthquakes/eventpage/us1000gez7/executive 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. GPS data support the hypothesis that the El Pilar fault is accumulating strike-slip strain, but there is a paucity of evidence that there is active convergence across the thrust fault. However, there does appear to be some small amount of contraction (Reinoza, et a.,. 2015). 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.
Motion histories of: North (NA) and South America (SA) relative to Indo-Atlantic hot spot (IAHS) Mu¨ller et al. (1993) reference frame (grey lines; NA wrt IAHS and SA wrt IAHS); hot spots relative to North America (dashed black line; IAHS wrt NA); Caribbean relative to North America (heaviest black line; Car wrt NA), as summarized from former relative positions of the Caribbean Trench (lighter black lines). Also shown: Cayman Trough (grey outline); Cenozoic convergence between the Americas (inset upper right; P88 ¼ Pindell et al. 1988; M99 ¼ Mu¨ller et al. 1999); seismic tomographic profile of van der Hilst (1990) (inset, lower right).
Location map of the active faults in northeastern Venezuela [Audemard et al., 2000] showing distribution of the GNSS stations: yellow squares, green circles, and red triangles are GNSS sites on which the acquisition campaigns were carried out in 2003, 2005, and 2013 respectively; the blue star corresponds to the cGNSS CUMA station of REMOS-IGVSB Network. We show the epicenter location of 1929 and 1997 events with their respective proposed ruptures (orange lines) [Audemard, 2007]. (top right) The inset box shows a schematic geodynamic map of the southeastern Caribbean [Audemard, 1999b; Audemard et al., 2000; Weber et al., 2001]. Legend: BF = Boconó Fault, EPF = El Pilar Fault, OAF = Oca Ancón fault, SMBF = Santa Marta Bucaramanga Fault, and SSF = San Sebastian Fault.
Observed velocities (white arrows) with error ellipses for 66% confidence level and simulated velocities (black arrows) according to the upgrade of displacement-simulation method. All displacements are based on the South America reference frame.
Simplified sections across the southeastern Caribbean margin (based on maps and sections by Bellizzia et al. (1976), Stéphan et al. (1980), Campos (1981), Beck (1986), Chevalier (1987); locations in Fig. 1).
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.
New: Magnitude 7.3 earthquake strikes in northern Venezuela, possibly the country’s largest earthquake in almost 200 years. Shaking was felt 1000s of kilometers away. (Image: USGS) https://t.co/bzgcagbZ5i pic.twitter.com/RLuSshccXD — Erik Klemetti (@eruptionsblog) August 22, 2018 Historical (~past century) seismicity in area of today's M7.3 quake in Venezuela at intermediate depth (~150 km). Today's event appears to be at edge of subducting slab (or at least its seismicity), with several historical events of similar magnitude and depth to North. pic.twitter.com/xdnHMKDolM — Jascha Polet (@CPPGeophysics) August 22, 2018 3D view of #earthquakes inside the earth along the SE edge of the Caribbean Plate. The large green dot is the hypocenter of todays M7.3 #VenezuelaEarthquake. (Colors indicate depth, size dot size indicates magnitude). https://t.co/MQYFz7UpWD pic.twitter.com/8dFWNuQ0K2 — IRIS Earthquake Sci (@IRIS_EPO) August 22, 2018 The 29 October 1900 M7.7 #Venezuela #earthquake was larger than today's (@Seismo_Steve). The ground shook for 50 seconds in Caracas. Charles Richter himself published a magnitude of M8.4. Other later magnitudes were smaller (Fiedler, 1988) but very few seismograms were recorded. pic.twitter.com/aKstkUkm1u — Dr. Kasey Aderhold (@kaseyaderhold) August 22, 2018 Global surface body wave record sections of the M7.3 #VenezuelaEarthquake https://t.co/OJJhV9lL7J pic.twitter.com/RbyBRid8ox — IRIS Earthquake Sci (@IRIS_EPO) August 22, 2018 It's been a busy few days for my @raspishake! The M7.3 Venezuelan earthquake was captured clearly in Turlock at 21:41:26 UTC… 9 min and 44 sec to travel the 4025 surface miles to Turlock!https://t.co/H3VRPKluBT pic.twitter.com/6El2CRBc1S — Ryan Hollister (@phaneritic) August 22, 2018 M7.3 earthquake today along the northern coast of Venezuela is one of the largest ever recorded earthquakes along the boundary between the Caribbean & South American plates. — Stephen Hicks (@seismo_steve) August 21, 2018 Mw=7.3, NEAR COAST OF VENEZUELA (Depth: 112 km), 2018/08/21 21:31:42 UTC – Full details here: https://t.co/fOGIcUNrDx pic.twitter.com/W6CukRFIxU — Earthquakes (@geoscope_ipgp) August 21, 2018 The moment of occurrence Powerful 7.3-magnitude earthquake rattles Venezuela Strong damage recorded in #TrinidadYTobago https://t.co/wjBOsdRIDW — live (@live1439) August 21, 2018 — flatearth world news (@FLATEARTHCENTER) August 21, 2018 Sismo pic.twitter.com/sw5fkIj764 — Juan Carlos Finol (@jcfinolb) August 21, 2018 M7 #earthquake #Venezuela: acceleration seismogram recorded at Grenville, Grenada about 200km northeast of the epicenter shows up to 2min of possibly felt shaking. https://t.co/9avYl65EZk pic.twitter.com/cbYrtb8XGs — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) August 21, 2018 M7.3 earthquake in Venezuela, ~150 km deep so low probability of a significant tsunami. Event has a reverse faulting mechanism, of which there have been a few in that area historically. https://t.co/bZ5BW9IfSc https://t.co/3oeIy3lwDM pic.twitter.com/Y2TDnTKiim — Jascha Polet (@CPPGeophysics) August 21, 2018 FirstMoMech: Mwp7.0 #earthquake Near Coast of Venezuela https://t.co/kCIw9Vypa6 pic.twitter.com/ly2iuEojzK — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) August 21, 2018 The 1766 eq, which could well be the predecessor of today's, was the largest one (Mw 7.8) in the CA-SA PBZ. It is interpreted as an intermediate-depth (60-200 km) eq. — Franck Audemard (@DrSeawater) August 22, 2018
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. 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 ≥ 6.5 (and down to M ≥ 4.5 in a second poster).
Seismotectonic setting of the Caribbean region. Black lines show the major active plate boundary faults. Colored circles are precisely relocated seismicity [1960–2008, Engdahl et al., 1998] color coded as a function of depth. Earthquake focal mechanism are from the Global CMT Catalog (1976–2014) [Ekstrom et al., 2012], thrust focal mechanisms are shown in blue, others in red. H = Haiti, DR = Dominican Republic, MCS = mid-Cayman spreading center, WP = Windward Passage, EPGF = Enriquillo Plaintain Garden fault.
Plate tectonic configuration of the Caribbean region showing the location of the study cases presented in this issue (numbers refer to papers, arranged as in the issue), and other important geological features of the region (compiled from several sources).
A. Tectonic map of Cayman trough region showing strike-slip faults (heavy lines), oceanic crust (gray) in Cayman trough, and magnetic anomaly identifications (numbered bars) (after Rosencrantz et a., 1988). Arrows show relative displacement directions. Fault zones: OFZ – Oriente; DFZ- Dunvale; EPGFZ – Enriquillo-Plantain Garden; WFZ – Walton; SIFZ – Swan Islands; MFZ – Motagua. Bl. Late Miocene reconstruction of Cayman trough. C. Early Miocene reconstruction.
Bathymetry of central Cayman Trough adapted from Jacobs et al. (1989). Contour interval: 250 m. Dotted line: location of gravity transect.
Finite fault model for tonight's M 7.6 EQ off Honduras – https://t.co/cEOVYyG2gP. Suggests relatively high slip, compact rupture. pic.twitter.com/tVvM5dHOy9 — Gavin Hayes (@gph_seismo) January 10, 2018 M7.6 Honduras quake is a left lateral strike-slip quake on the Swan Islands Transform Fault pic.twitter.com/pRofV9d9g0 — Jascha Polet (@CPPGeophysics) January 10, 2018 Today's M7.6 quake near Honduras occurred where the velocity on the Carribean – North American plate boundary is parallel to the boundary, and thus a strike-slip quake (figure adapted from DeMets et al., 2000) pic.twitter.com/ExKf2svi95 — Jascha Polet (@CPPGeophysics) January 10, 2018 Interested in seeing real-time seismograms of the #Honduras #earthquake? Select any seismic station to view data.https://t.co/XYHjPlTAFC pic.twitter.com/lnqNtUaLWE — IRIS Earthquake Sci (@IRIS_EPO) January 10, 2018 Mw=7.5, NORTH OF HONDURAS (Depth: 15 km), 2018/01/10 02:51:31 UTC – Full details here: https://t.co/lStlUFIbrU pic.twitter.com/XYTsRVUkag — Earthquakes (@geoscope_ipgp) January 10, 2018 This great overview map + explanations of the "Seismotectonics of the Caribbean Region and Vicinity" may be found at the USGS: https://t.co/vFh6AeD8hh pic.twitter.com/DLzLdRWvlC — Jascha Polet (@CPPGeophysics) January 10, 2018 'Tectonic Aspects of the Guatemala Earthquake of 4 February 1976' | Science https://t.co/HKFjwzeYN7 — Ken Hudnut (@kwhudnut) January 10, 2018 What is that #earthquake beach ball? https://t.co/jf2cH7W4bl pic.twitter.com/QyY3G9iSrR — IRIS Earthquake Sci (@IRIS_EPO) January 10, 2018 Autogenerated responses out to 1400km for peak ground displacements from geodetic obs. @UNAVCO for M7.6 44km E Great Swan Is. Honduras 2018-01-10 earthquake pic.twitter.com/rapjF3k8g4 — UNAVCO (@UNAVCO) January 10, 2018 #RT magnitude 7.6 #earthquake #honduras as seen on #raspberryshake #personal #seismograph in #Tegucigalpa and my #home in #Panama pic.twitter.com/ZOBKKObR6o — Raspberry Shake (@raspishake) January 10, 2018 Nobody felt this shaking – but waves from the M7.6 Honduras earthquake rolled through #Victoria and #Vancouver last night after travelling nearly 5000 km in about 10-20 minutes. #NRCanSci pic.twitter.com/LNNJjBpG1R — John Cassidy (@earthquakeguy) January 10, 2018 @UNAVCO Science Snapshot About Plate Motions in Caribbean near M7.6 44km E Great Swan Is. Honduras earthquake sets the geodynamics, https://t.co/xtTqjw40i7 pic.twitter.com/oQDCSm2JLh — UNAVCO (@UNAVCO) January 10, 2018 temblor post with Shinji Toda static coulomb modeling shows increase in likelihood of earthquake on this plate boundary fault system adjacent to Cayman troughhttps://t.co/IycXcW8oNU pic.twitter.com/wJPfrd5JYD — patton_cascadia (@patton_cascadia) January 10, 2018 The Mw 7.5 Honduras earthquake recorded in New Zealand, more than 12 000 km from the epicentre. Selected #GeoNet stations are shown north-to-south, P-wave arriving ~15 min after the origin time. pic.twitter.com/vA2Vs0z6Eg — John Ristau (@SinistralSeismo) January 10, 2018 Looks like a nice example of the passage of the surface waves from a large regional earthquake dynamically triggering an earthquake in a volcanic area https://t.co/rdosRnQtPn — Jascha Polet (@CPPGeophysics) January 11, 2018
There was a fascinating earthquake sequence a few days ago on and offshore of Guatemala. Offshore of Guatemala in the Pacific Ocean, the Cocos plate subducts beneath the North America and Caribbean plates (NAP & CP). The transform plate boundary between the NAP and CP forms the Motagua-Polochic fault zone onshore, which bisects Guatemala. From late May 2017 through mid June there were several earthquakes with the largest magnitude M = 5.5. These earthquake hypocenters have depths that are deeper and shallower than the estimated depth for the subduction zone fault (Hayes et al., 2012), but many of the earthquakes simply have a default depth of 10 km. So it is difficult to say if these are all near the megathrust or are on upper plate faults (e.g. in the accretionary prism). These earthquakes have compressional fault plane solutions. Either way, they appear to have loaded some faults down-dip along the subducting slab. This may or may not be the case, but there was a deep extensional magnitude M 6.9 earthquake (with an aftershock of M = 5.1 nearby). These along dip earthquakes are probably related. I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend).Earthquake Report: Cayman Islands
I am in Portland, Oregon this week, attending the Winter National Tsunami Hazard Mitigation Program Meeting. While one of our workshops, several of us got an alert about a M 7.3 earthquake offshore of Cuba and Jamaica. My colleagues from Puerto Rico were immediately interested to learn more about this. We noticed that nothing was being posted to tsunami.gov.
https://earthquake.usgs.gov/earthquakes/eventpage/us60007idc/executive
The location is familiar with me as I have written reports for earthquakes in this region over the past couple of years. This earthquake happened along a strike-slip plate boundary fault. Thus, the chance of a large tsunami is low. However, strike-slip earthquakes DO generate tsunami, albeit smaller than those created by subduction zone earthquakes. In addition, earthquakes can trigger submarine landslides, which can also serve to cause tsunami (these can be very large, but generally impact the area near the landslide, like the 1998 Papua New Guinea tsunami.).
In a few minutes, the earthquake magnitude was updated to M 7.7. This is quite common, as seismological data are analyzed with greater detail after the initial automatic magnitude calculation.
A few minutes later, the USGS moment tensor (earthquake mechanism) was posted online, confirming that it was a strike-slip earthquake.
The IOC tide gage network was not working, so I could not check for tsunami observations until later. However, the Pacific Tsunami Warning Center sent out an email to the International Tsunami Bulletin Board (email list restricted to tsunami scientists) with arrival times. There was a suggestion that tsunami waves up to 1 meter may arrive along the coast in the region.
At lunch time, I went to my hotel room to put together an interpretive poster (thanks boss!) to send out on social media. By that time, a small tsunami wave had been observed at the tide gage on the west coast of Cayman Island. The PTWC sent out their final email, stating a 0.4 foot tsunami was recorded there. I went to the IOC website and the gage data were quite noisy, but it matched the PTWC email. Here is a link to the George Town Tide Gage.
Just as I was about to tweet the poster, the USGS earthquake fault slip model was published online (so I added that to the poster).
After lunch, as the workshop continued, there was a M 6.1 earthquake. I noticed it was west of the slip model. I had considered an alternate hypothesis (that the M 6.1 was triggered, not an aftershock), but now think that this is just part of the M 7.7 slip patch. Looking at the back projection data from IRIS, it suggests that this earthquake initiated in the east and propagated to the west. It makes sense to me that the fault reached a zone where the fault slip slowed down, until it reached the patch that slipped during the M 6.1. (simplifying this for this report)
Was this Cayman Islands Earthquake Sequence related to the ongoing Puerto Rico Earthquake Sequence? Probably not. They are simply too far from each other.
There are two types of earthquake triggering: static and dynamic. Triggering happens when an earthquake on one fault changes the stress on a different fault, causing that other fault to slip during an earthquake. These stress changes are small, so the “receiver” fault needs to be at a state of stress that is high enough that it would be almost ready to slip before the “source” earthquake.
Dynamic triggering happens when seismic waves from the source earthquake travel through the Earth, triggering an earthquake on the receiver fault. These changes in stress may take a while before the triggered earthquake happens, but generally, we think that this would happen while these waves are traveling through the area.
Static triggering happens when a source earthquake changes the stress in the crust surrounding the source earthquake. This change typically lasts months to years and won’t extend beyond two fault lengths of the source earthquake. So, If the source quake had a rupture length of 50 km, static triggering probably would not happen more than 100km from the source quake. This is just a rule of thumb… BUT the M 7.7 is very far from Puerto Rico, so is probably unrelated to the Puerto Rico Sequence.Earthquake Description
Further to the east, this plate boundary changes into a subduction zone along the Lesser Antilles. This subduction zone is the source of a great amount of research. There is some evidence that the megathrust subduction zone fault is not locked, so it is slipping and not capable of generating Great (M>8) earthquakes. However, I was on a team of French geologists aboard the Pourquoi Pas? in 2016. We were coring the deep sea to investigate the sedimentary record of Great earthquakes. Based on our analysis, it appears that the fault is capable of producing these large earthquakes, but the average time between earthquakes (the recurrence interval) is on he order of several millenia.
To the west of the M 7.7 earthquake, there is an oceanic spreading ridge where crust is created, forming the Cayman Trough. As the boundary steps to the south, the relative plate motion is focused on another left-lateral strike-slip fault, the Swan Island fault. This fault extends further to the west into Central America and turns into the Motagua Polochic fault system (there are actually multiple faults hypothesized to be the active part of this plate boundary here). I discuss this more in an Earthquake Report here.Below is my interpretive poster for this earthquake
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Some Relevant Discussion and Figures
Caribbean Earthquake Reports
General Overview
Earthquake Reports
Social Media
2020-01-28 19:10:25 (UTC) pic.twitter.com/Oiyj7sFzuT
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
Earthquake Report: Puerto Rico!
Since late December, southwestern Puerto Rico has seen a sequence of smaller (M3-5) earthquakes, culminating with the 29 Dec 2019 M 5 which later turned out to be a foreshock (there was also a M 4.7 that was a foreshock to the M5). Then on 6 Jan, there was a M 5.8, which was now the mainshock. Then, on the following day, there was the real mainshock, the M 6.4. Lots of other earthquakes too. The largest aftershock was the M 5.9 on 11 Jan. Below I include some comparisons for the M 6.4 and M 5.9 quakes.
Here is a plot showing the cumulative energy release from this sequence. I used the USGS NEIC earthquake catalog for events M≥0. Time is on the horizontal axis and energy release (in joules) on the vertical axis. For every earthquake, the plot steps up relative to the energy released by that quake.
These earthquakes in Puerto Rico have been deadly and damaging. Many structures there are constructed with soft stories on the ground level (the buildings are uplifted to mitigate hurricane flood hazards). Unfortunately, these soft story structures don’t perform well when subjected to earthquake shaking. Thus, there have been many structure collapses. Luckily, there have been only a few deaths. While we may all agree that having no deaths is best, there could have been more.
The M 6.4 even generated a small tsunami. This was localized and was observed clearly on only one tide gage (The Magueyes Island gage).
Here is the tsunami record, along with a map showing the location of the tide gage in southwestern Puerto Rico. These data are from a site that is my “go-to” website for looking for tsunami in tide gage data. I generally look here first.
USGS Earthquake Event Pages
Here is a screenshot of the forecast updated today (12 Jan 2020). Head to the USGS site to stay up to date.
UPDATE: 2020.02.02 -palindrome day!
Below is my interpretive poster for this earthquake
Background Information
section is shown by a black rectangle on the top map.
Tectonic Strain and Seismic Hazard
Earthquake Shaking Intensity
Earthquake Triggered Landslides
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.
Surface Deformation from Remote Sensing
Caribbean Earthquake Reports
General Overview
Earthquake Reports
Social Media
Thanks to the seismic network of Puerto Rico through IRIS pic.twitter.com/EZoJnIEozu
For the past 11 days, the US territory of Puerto Rico has been shaken by hundreds of earthquakes, culminating in a magnitude 5.8 temblor on Monday and a deadly magnitude 6.4…https://t.co/2FQ9tV8HlU #PuertoRicoEarthquake pic.twitter.com/21iIa6Tz8v
Video desde #Guánica justo que en el momento que un #sismo #réplica termina de colapsar la torre de una iglesia
Via Luis Alberto Románhttps://t.co/OZ2dztAA2x pic.twitter.com/GijFbTnayj
and doi: 0.1785/0120160198 pic.twitter.com/PBgrDlIrk5
(with the usual caveats for near real-time local catalog: changes in catalog completeness and network configuration with time are common when large quakes occur) pic.twitter.com/guhuUodobqUPDATE 2020.01.14
UPDATE 2020.01.25
Maximum magnitudes show a general decreasing tendency since January 07, 2020.
Data from @redsismica of PR! #TemblorPR @DavidBegnaud @adamonzon #EarthquakePR pic.twitter.com/Ag6xErR4My
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
Earthquake Report: 2010 Haiti M 7.0
https://earthquake.usgs.gov/earthquakes/eventpage/usp000h60h/executive
Here I review some of the earthquake related materials from this temblor.
The M 7 earthquake happened on a strike-slip fault system that accommodates relative plate motion between the North America and Caribbean plates. There is a history and prehistory of earthquakes on this fault system.
This event was quite deadly. Here is a comparison of this earthquake relative to other earthquakes (Billham, 2010).
Below is my interpretive poster for this earthquake
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Resources Canada. b, Position time series at station DFRT (orange arrow labelled on a) showing four pre-earthquake measurement epochs and the post-earthquake epoch. Note the steady interseismic strain accumulation rate and the sudden coseismic displacement.
Earthquake Stress Triggering
thrust). Major cities are noted by green circles.
Earthquake Humanitarian Impact
Earthquake Shaking Intensity
Earthquake Triggered Landslides
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.
landslides per 0.01° latitude; circles are individual landslide locations scaled by area (see legend in panel g). Thin black dashed lines are areas affected by the landslides; thick black dashed lines are mean local relief of coseismically uplifted and subsided areas. (f and g) Histograms of (f) point density [km−2] and (g) rate [%] of re-activated landslides for 0.01° latitude bins; PaP: Port-au-Prince; PG: Petit Goave.
Earthquake Triggered Turbidity Currents
Earthquake Triggered Tsunami
Caribbean Earthquakes
General Overview
Earthquake Reports
Social Media
References:
Basic & General References
Specific References
during the 2010 Haiti earthquake in Nature Geoscience, http://www.nature.com/doifinder/10.1038/ngeo992Return to the Earthquake Reports page.
Earthquake Report: Guatemala and Mexico
https://earthquake.usgs.gov/earthquakes/eventpage/us2000jbub/executive
Offshore of Guatemala and Mexico, the Middle America trench is formed by the subduction of the oceanic Cocos plate beneath the North America and Caribbean plates.
To the east of Guatemala and Mexico, the North America and Caribbean plates are separated by a left lateral (sinistral) strike-slip plate boundary fault (that forms the Cayman Trough beneath the Caribbean Sea).
As this plate boundary comes onshore, this fault forms multiple splays, including the Polochi-Montagua fault. As this system trends westwards across Central America, it joins another strike-slip plate boundary associated with the subduction zone (the Volcanic Arc fault).
South of about 15°N, the relative plate motion between the Caribbean and Cocos plates is oblique (they are not moving towards each other in a direction perpendicular to the subduction zone fault). At plate boundaries where plate convergence is oblique (like also found in Sumatra), the strain is partitioned onto the subduction zone (for fault normal component of the relative plate motion) and a forearc sliver fault (for the fault parallel relative motion).
The Tehuantepec fracture zone (TFZ) is a major structure in the Cocos plate. Coincidentally, the strike-slip fault systems trend towards where the TFZ intersects the trench.
There is left-lateral offset of the seafloor across the TFZ so the crust is about 10 million years older on the north side of the eastern TFZ. This age offset changes the depth of the crust across the TFZ and also may affect the megathrust fault properties on either side of the TFZ.
In addition, the TFZ may have geological properties that also affect the fault properties when this part of the plate subducts (affecting where, when, and how the fault slips).
There are so many things going on, but I will mention one more thing. Something that also appears to be happening in this part of the subduction zone is that there may be gaps in the slab beneath the megathrust. If this is true (Mann, 2007), then there may be changes in slab pull tension along strike as a result of different widths of attached downgoing slab.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
Age of Oceanic Lithosphere
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
In 2017 there was a series of large magnitude earthquakes in the region of today’s M=6.6 and further to the south. These quakes are highlighted in the posters above, notable are the 6 Jun M=6.9 and 22 Jun M=6.8. The first quake was a deep extensional event, followed by a thrust event (possibly triggered by the M=6.9). In addition, there was a M=6.9 extensional earthquake in 2014 that also may have been a player.
I presented an interpretive poster showing the zone of aftershocks associated with the June sequence. Later, in Sept, there was a M=8.2 extensional tsunamigenic earthquake to the north of the June sequence. If we look at the aftershock zone for the M=8.2 quake, it looks like a sausage link adjacent to the sausage link formed by the June aftershocks. mmmm veggie sausages.
However there was no megathrust earthquake in the area of the M=8.2 sequence.
Other Report Pages
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
Mexico | Central America
Earthquake Reports
Social Media
References:
in northern Central America: Geological Society of America Special Paper 428, p. 1–19, https://doi.org/10.1130/2007.2428(01).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 Report: Venezuela
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. 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:
Caribbean Earthquake Reports
General Overview
Earthquake Reports
Chile | South America
General Overview
Earthquake Reports
Social Media
There was an M7.7 quake to the west in 1900 but this will have preceded detailed instrumental recordings pic.twitter.com/e9HY0inE9E
In the same depth range of today eq??? https://t.co/vKTOv9UC7m
References:
DOI: 10.1144/SP328.1
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≥Earthquake Report: 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.Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange) for the M 7.3 earthquakes, in addition to some relevant historic earthquakes.There have been several M 6.7-M 7.5 earthquakes to the west of this fault in the last 4 decades or so.
I include some inset figures.
2018-01-10 02:51:31 UTC 17.469°N 83.520°W 10.0 km depth
https://earthquake.usgs.gov/earthquakes/eventpage/us1000c2zy#executive
1976-02-04 09:01:43 UTC 15.324°N 89.101°W 5.0 km depth
https://earthquake.usgs.gov/earthquakes/eventpage/usp0000ex3#executive
1992-05-25 16:55:04 UTC 19.613°N 77.872°W 23.1 km depth
https://earthquake.usgs.gov/earthquakes/eventpage/usp000582h#executive
1999-07-11 14:14:16 UTC 15.782°N 88.330°W 10.0 km depth
https://earthquake.usgs.gov/earthquakes/eventpage/usp0009bed#executive
2004-12-14 23:20:13 UTC 18.958°N 81.409°W 10.0 km depth
https://earthquake.usgs.gov/earthquakes/eventpage/usp000daqt#executive
2009-05-28 08:24:46 UTC 16.731°N 86.217°W 19.0 km depth
https://earthquake.usgs.gov/earthquakes/eventpage/usp000gxkj#executive
Social Media
UPDATE: 2018.01.10
Regional Seismicity
Caribbean
General Overview
Earthquake Reports
Mexico | Central America
General Overview
Earthquake Reports
References:
Earthquake Report: Guatemala
Below is my interpretive poster for this earthquake.
I include some inset figures in the poster.
Here are the USGS webpages for the earthquakes with moment tensors plotted above
Mexico | Central America
Earthquake Reports
References