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.
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
- 2019.12.29 M 5.0
- 2020.01.06 M 5.8
- 2020.01.07 M 6.4
- 2020.01.06 M 5.6
- 2020.01.10 M 5.2
- 2020.01.11 M 5.9
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
- Speaking of aftershocks, here is a tweet that discusses what aftershocks and how we use the temporal distribution of earthquake size to distinguish between a typical foreshock-mainshock-aftershock sequence.
- The graphic below was prepared by the Swiss Seismological Service and ETH Zurich for their discussion about these two phenomena. There is probably a continuum between these two, but there was some debate about this on the twitterverse today.
- Now compare with this figure from Dr. Kasey Aderhold. Dr. Aderhold put this together to compare these earthquakes with the figure above. Sr. Aderhold is who shared that link on social media (in social media section below).
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.
UPDATE: 2020.02.02 -palindrome day!
Below is my interpretive poster for this earthquake
- I plot the seismicity from the past 2 months, with diameter representing magnitude (see legend). I include earthquake epicenters from 1920-2020 with magnitudes M ≥ 5.0.
- I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
- A review of the basic base map variations and data that I use for the interpretive posters can be found on the Earthquake Reports page.
- Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.
- Here is the map with 2 month’s seismicity plotted.
- I digitized Bruna et al. (2015) fault lines. To the southeast of the M 6.4 there is mapped a northeast striking (trending) normal fault that dips to the northwest. This seemed to be the best candidate as a source for the M 6.4 earthquake. The earliest earthquakes were strike-slip oblique-normal events, so initially I thought this was a strike-slip sequence. But, as quakes kept happening, they had more extensional mechanisms.
- To the east of the hypothetical M 6.4 source normal fault there are 2 pairs of opposing normal faults. These look typical of a transtension configuration (a strike-slip fault setting with fault geometry that includes extension parallel to the strike-slip faults). These 2 pairs of faults appear to be forming tectonic basins. The M 6.4 hypothetical source fault does not have a mapped counterpart, but the location of that hypothetical counterpart would be close to the shoreline (so could have been missed by the marine geologists who mapped the other faults further offshore).
- Below these interpretive posters, I include an animation from Dr. Anthony Lomax below that shows a better view of this hypothetical fault geometry.
- This is an earlier poster from 7 Jan, which has a couple inset figures.
- In the upper left corner is a tectonic overview map from Symithe et al. (2015). I placed a blue star where the M 6.4 is located.
- In the upper right corner is a regional-scale earthquake fault map from Bruna et al. (2015). The blue star appears again.
- In the lower right corner I show the Bruna map with seismicity plotted. I georeferenced the Bruna map and labeled some of the faults mapped by Bruna et al. (2015).
- This is the interpretation poster from the 29 December 2019 M 5.0 earthquake. I included the earthquake from a more zoomed out (small scale) view.
- In the upper left corner is a general view of the faults in Puerto Rico (Piety et al., 2018). I placed a blue star in the location of the M 6.4 earthquake. There are many more faults plotted in the upper right figure from Bruna et al. (2015).
- The M 6.4 was the most damaging earthquake in Puerto Rico since the 1918 earthquake as shown on this poster. Note how both the 2020 M 6.4 and the 1918 M 7.1 were normal type (extensional) earthquakes.
- Here is the interpretive poster for the 2010 Haiti M 7.0 earthquake. Check out how there are more tectonic basins to the west of Puerto Rico.
- Here is the animation from Dr. Anthony Lomax. He states that he “relocated seismicity M1.0+ using Lin & Huérfano 2011 Min 1D model & NonLinLoc-EDT with station corrections. The animation shows seismicity aligned to dip to the northwest.” This matches the hypothetical source fault mapped by Bruna et al. (2015). VERY COOL!
- Here is the tectonic map from Symithe et al. (2015). Puerto Rico is in a place where the plate boundary between the North America and Caribbean plates transitions from subduction (to the east, the Lesser Antilles) to transform (to the west, the Greater Antilles). The Lesser Antilles Great (M>8) earthquake recurrence appears to be several thousand years (based on turbidite stratigraphy from our 2016 cruise). We currently don’t know how far west of the Aves Ridge that subduction zone earthquakes happen. It is possible, but the convergence is highly oblique, similar to the northern part of the 2004 Sumatra-Andaman subduction zone earthquake. Interestingly, there is a series of spreading ridges and transform faults to the east of the Sunda trench (in the Andaman Sea), just like there are the same features to the west of the Greater Antilles (e.g. the Cayman Trough).
- This is another map showing earthquake history, fault location, and earthquake slip direction from Calais et al. (2016). Note how the relative plate motion near Puerto Rico is oriented parallel to the plate boundary (the Puerto Rico trench). This suggests that most of the plate motion would result in strike-slip earthquakes. However, the relative motion is oblique, so subduction zone earthquakes are still possibble.
- Here are some figures from Bruna et al. (2015). First I present their tectonic overview figure.
- Here is a map that shows the major earthquake faults in Puerto Rico (Piety et al., 2018). There are many more.
- This is the fault map that I used to digitize fault data in my posters above (Bruna et al., 2015). These faults were mapped using bathymetric mapping and seismic reflection analyses.
- This plot shows the GPS observations in the Caribbean. Symithe et al. (2015) used these data to estimate the amount of seismogenic coupling (how much the faults are “locked”) in the region.
- This map shows cross sections of seismicity in the region (Symithe et al., 2015). The profile for Puerto Rico is B-B.’ Note that subduction from the north is reasonable given the seismicity, while subduction from the south is not supported by the seismicity. Recall that the absence of evidence is not evidence of absence and that the Cascadia subduction zone lacks seismicity but we have a 10,000 year record of megathrust subduction zone earthquakes there. In other words, just because there is no seismicity, that does not mean that there is no active subduction potentially leading to subduction zone type earthquakes.
- Here is another hypothetical view of the plate configuration from Xu et al. (2015). Note the regions of extension, one to the northwest of Puerto Rico (the Mona Rift, which also just had a large earthquake near the 1918 quake) and the Anegada Passage (AP).
- Speaking of the recent quake in the Mona Rift, here is my interpretive poster for that sequence. As we saw in Xu et al. (2015), the Mona Rift is an area where the crust is stretching in an east-west direction. The 1918 M 7.1 earthquake and the 24 September 2019 M 6.0 Mona Rift earthquakes are extensional in an east-west direction. There were about 100 fatalities and there was millions of dollars of damage. The Puerto Rico Seismic Network has a review page for the 1918 earthquake.
- Here are some plots showing GPS motion rates relative to topography and seismicity in the region (Symithe et al., 2015).
- First, look at the profile that crosses Haiti, A-A’ (south to north, from left to right).The profile for Haiti clearly shows steps in the GPS velocity profiles. This is evidence for strike-slip faults as tectonic strain from relative plate motions is accumulated along fault boundaries, there are steps in the plate motion rates. These steps are located where the profile crosses two major strike slip faults in Haiti.
- Next look at profile B-B’ which crosses Puerto Rico. There is no observed strike-slip strain accumulating in Puerto Rico, except there is a step in the north, far offshore of Puerto Rico. There exist several major active strike-slip faults in Puerto Rico, but they are not found in these geodetic data (PIety et al., 2018).
- This is a larger scale view of GPS site motion in the region from Calais et al. (2016).
- While this does not implicate these earthquake sequence, it helps us get a comprehensive view of the tectonics of Puerto Rico. First I show the faults used in their model, then I show the figure showing how much these authors estimate that the faults are locked.
- Here is another view of plate coupling for the region from Manaker et al. (2008). Apologies for the resolution as this may remind us all to provide high quality figures to the publisher of our journal articles.
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.  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
section is shown by a black rectangle on the top map.
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).
Tectonic Strain and Seismic Hazard
- As the tectonic plates move relative to each other, and stuck earthquake faults resist this motion, the crust surrounding and including these faults can deform to change shape and volume. This change in shape or volume is called strain.
- Regions of high tectonic strain are areas that are changing shape or volume more than in areas of low strain. The map below shows a Global Strain Rate Map for the region (Kreemer et al., 2014).
- These figures show the chance of the region will experience ground shaking over a period of 50 years (the life of a building) from Mueller et al. (2010). These maps show the chance that a region will shake with a given acceleration (units are in percent g, where g = gravity; if the ground shakes with accelleration exceeding 100% g, then rocks and other things can be thrown into the air).
- Many of us are familiar with the concept of the 100 year flood, a flood that may occur every 100 years on average. However, there could be more than one 100 year flood in a year because it is just a statistical average that can change with time. The same is true for earthquake statistics.
- Basically, the 2% in 50 year map represents the 250 year earthquake. The 10% in 50 year map represents a 500 year earthquake.
- Read more about the statistics used in these seismic hazard maps here.
- The USGS National Seismic Hazard Site is here.
Earthquake Shaking Intensity
- Here is a figure that shows a more detailed comparison between the modeled intensity and the reported intensity, for both the M 6.4 and M 5.9 events. Both data use the same color scale, the Modified Mercalli Intensity Scale (MMI). More about this can be found here. The colors and contours on the map are results from the USGS modeled intensity. The DYFI data are plotted as colored polygons (color = MMI, labeled as “dyfi x.x”).
- In the lower center are plots showing MMI intensity (vertical axis) relative to distance from the earthquake (horizontal axis) for each event. The models are represented by the green and orange lines. The DYFI data are plotted as light blue dots.
- What do you think? Do these earthquake intensity models (from the USGS) match the observations? What do you think may control how well they do or do not fit the model? What might affect ground shaking locally or regionally?
- Here is a video from IRIS that helps us learn about what controls the 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:
- Here is a map that I put together using the data available from the USGS Earthquake Event pages. More about these models can be found here.
- The map on the left shows liquefaction susceptibility from the M 6.4 and the map on the right is for the M 5.9 earthquake. The M 6.4 event affects a much more broad region with greater intensity.
- These models use empirical relations (earthquake data) between earthquake size, earthquake distance, and material properties of the Earth.
- The largest assumption is that for the Earth materials. This model uses a global model for the seismic velocity in the upper 30 meters (i.e. the Vs30). This global model basically takes the topographic slope of the ground surface and converts that to Vs30. So, the model is basically based on a slope map. This is imperfect, but works moderately well at a global scale. A model based on real Earth material data would be much much better.
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.
Surface Deformation from Remote Sensing
- Dr. Eric Fielding used satellite data (“Interferometric Synthetic Aperture RADAR,” or “InSAR”) to estimate how much the ground surface moved. Below is the first result where red
- 2016.01.17 1900-2016 Summary northern Caribbean
- 2020.01.07 M 6.4 Puerto Rico
- 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 Earthquake Reports
- Perhaps the most important job.
— 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)
Thanks to the seismic network of Puerto Rico through IRIS pic.twitter.com/EZoJnIEozu
— Bertrand Delouis (@BertrandDelouis) January 7, 2020
— 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
— 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
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
— Berkeley Seismo Lab (@BerkeleySeismo) January 7, 2020
— IRIS Earthquake Sci (@IRIS_EPO) January 7, 2020
#PuertoRico 🇵🇷 en estado de emergencia, tras los fuertes sismos de hoy.
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
— 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
— temblor (@temblor) January 8, 2020
— temblor (@temblor) January 8, 2020
— 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
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
(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/guhuUodobq
— 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.
Maximum magnitudes show a general decreasing tendency since January 07, 2020.
Data from @redsismica of PR! #TemblorPR @DavidBegnaud @adamonzon #EarthquakePR pic.twitter.com/Ag6xErR4My
— Janira Irizarry (@jany_ip) January 25, 2020
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Basic & General References
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