A magnitude 6.4 earthquake shook southwestern Puerto Rico this morning (Jan. 7), according to the U. S. Geological Survey (USGS); this is the largest yet in a series of quakes that have hit the region.
At least one person died as walls collapsed around the area, and eight more people were injured, according to NPR. Electricity went out across Puerto Rico as automated systems shut down the island’s power plants, recalling power outages that lasted 11 months after Hurricane Maria, which caused the worst blackout in US history. The North American and Caribbean tectonic plates meet in this area, but the quake doesn’t appear to be the result of those plates grinding together, according to USGS. Instead, a release of energy and stress inside the Caribbean plate seems to have caused the shaking.
A day earlier, a smaller, 5.8 magnitude quake in the same area destroyed a natural rock archway along the coast known as the Punta Ventana, NPR reported. Since a 4.7 magnitude earthquake struck the area on Dec. 28, 2019, more than 400 quakes of at least magnitude 2 have hit Puerto Rico’s southwest region. Eleven have been magnitude 4 or greater, according to USGS.
(The numbers used to measure quakes are nonlinear. A magnitude 3 quake is 10 times as powerful as a magnitude 2 quake, and a magnitude 4 quake is 10 times as powerful as a magnitude 3 quake and so on.)
Puerto Rico’s governor, Wanda Vázquez, suspended work for the day for public sector workers who aren’t first responders.
Update May 29 13:19 UTC : Local reports are mentioning houses with cracks in Salva León de Higuey
Update 22:24 UTC : List of the most recent earthquakes closest to today’s epicenter. Interesting to see is that almost all of these earthquakes are very deep, this due to the movement of the Oceanic plate towards the south (she dives below the Caribbean plate). The tectonics of this Caribbean area are very complex with a number of sub-plates as well as dangerous transform faults, like the one who generated the cruel Haiti earthquake. Transform faults are resulting in a mainly horizontal movement which can generate a lot of damage to not properly build houses.
Update 22:24 UTC : Below the seismogram of this earthquake as recorded in Presa de Sabenta, Dominican Republic
Update 21:57 UTC : The main reason why this earthquake was felt in such a wide radius (Puerto Rico and Dominican Republic) is the depth of the hypocenter or breaking point. Although the radius is very wide, the concentrated shaking at the epicenter is luckily also a lot weaker. When this earthquake would have been shallower the risk on serious damage would have been a lot bigger.
Update 21:46 UTC : USGS has increased the Magnitude again to M5.8 at the same depth. Below the shaking intensities for the most important cities close to the epicenter.
Update 21:39 UTC : USGS has recalculated the Magnitude and has set it now to M5.7 at a depth of 91 km. USGS projects a max. Moderate shaking in the eastern part of the Dominican Republic and a weak shaking in Puerto Rico.
Update 21:35 UTC : The earthquake will surely NOT generate a tsunami.
Update 21:32 UTC : The preliminary earthquake Magnitude values are in between 5.3 and 5.8 at a depth of 100 km. This means that there is only a limited chance on serious damage. The deeper the hypocenter is, the less chance on damage.
Update : Below the Focal Mechanism or Beach Ball of this earthquake. It shows a clear compression
31km (19mi) ESE of Boca de Yuma, Dominican Republic
37km (23mi) S of Punta Cana, Dominican Republic
55km (34mi) SE of Salvaleon de Higuey, Dominican Republic
68km (42mi) ESE of La Romana, Dominican Republic
175km (109mi) E of Santo Domingo, Dominican Republic
Update 11:43 UTC : Many people living in the coastal areas auto-evacuated their houses in search for higher ground. An idea earthquake-report.com welcomes as waiting for official alerts always has a small risk.
Update 09:17 UTC : There were also power cuts who where restored shortly after the quake. Due these power cuts the Puerto Rico Seismic Network ceased operations a few seconds after the earthquake occurred !
Many people left their houses in search for higher grounds
Understanding the January 13 Puerto Rico earthquake
The January 13, 2014 M 6.4 earthquake north of Puerto Rico occurred as a result of oblique-thrust faulting. Preliminary faulting mechanisms for the event indicate it ruptured either a structure dipping shallowly to the south and striking approximately east-west, or a near-vertical structure striking northwest-southeast. At the location of this earthquake, the North America plate moves west-southwest with respect to the Caribbean plate at a velocity of approximately 20 mm/yr, and subducts beneath the Caribbean plate at the Puerto Rico Trench. The location, depth and mechanism of the earthquake are consistent with the event occurring on this subduction zone interface.
While the Puerto Rico Trench is known to be a significant seismic hazard, and is capable of hosting M8+ earthquakes, moderate-to-large events on the subduction zone are rare.
Over the past century, three such events have occurred nearby to the January 13, 2014 earthquake – a M 6.6 event in 1915, just to the east of the 2014 event; a M 7.0 earthquake 70 km to the west in 1917; and a M 7.6 earthquake in 1943 just northwest of the 2014 earthquake. Two earthquakes occurred in the Mona Passage approximately 100 km to the southwest of the 2014 earthquake in 1916 (M 7.0) and 1918 (M 7.3), while the 1946 M 7.9-8.0 Hispaniola earthquake struck 230 km to the west, also on the North America slab interface. The July 1943 North Mona Passage earthquake did not cause significant damage in Puerto Rico, though it did spawn a small tsunami, and was the first in a series of large events in the broader northern Caribbean region between central Hispaniola and Puerto Rico over the following decade, including the larger 1946 earthquake. The 1946 event is known to have caused significant damage in both Hispaniola and Puerto Rico, including destruction from a subsequent tsunami.
Update 06:53 UTC : Some minor damage is reported from Puerto Rico. Nothing serious, but people are mentioning cracks in walls.
Twitter damage image from Puerto Rico
Update 05:06 UTC : USGS has lowered the shaking intensity after recalculations. We do confirm that the new numbers are much more reflecting what our readers are telling us.
Update 05:04 UTC : NO reports of serious damage has reached us so far. Broken falling objects are reported bu that happens often in case of moderate shaking.
Update 04:59 UTC : It would be wise NOT to swim in the ocean the next hours as strong currents could have been generated by the earthquake. Almost nobody will do so as it is night at the moment in Puerto Rico
Update 04:58 UTC : The earthquake occurred in the deep Ocean Trench. This was not the strongest earthquake in the area so far. As can be seen on our bottom map, a M7.3 Magnitude earthquake happened right below Puerto Rico in 1918!
Official Tsunami statement of the PTWC :
A DESTRUCTIVE WIDESPREAD TSUNAMI THREAT DOES NOT EXIST BASED ON HISTORICAL EARTHQUAKE AND TSUNAMI DATA.
HOWEVER – THERE IS THE SMALL POSSIBILITY OF A LOCAL TSUNAMI THAT COULD AFFECT COASTS LOCATED USUALLY NO MORE THAN A HUNDRED KILOMETERS FROM THE EARTHQUAKE EPICENTER. AUTHORITIES IN THE REGION NEAR THE EPICENTER SHOULD BE MADE AWARE OF THIS POSSIBILITY.
Update 04:39 UTC : The pictures below are showing the theoretical shaking intensity. In general we can say that this was a lucky escape for Puerto Rico. 30 km more to the south and serious damage could have been expected at the Northern Puerto Rico coast.
Update : The shaking intensities as reported by our readers in Puerto Rico are leveraging a light to moderate shaking – weak shaking in the Dominican Republic
NO risk for a tsunami
Theoretical calculations from USGS are expecting a strong shaking at the northern coast of Puerto Rico
56km (35mi) N of Hatillo, Puerto Rico
58km (36mi) NNE of Isabela, Puerto Rico
59km (37mi) NNW of Arecibo, Puerto Rico
67km (42mi) NNW of Barceloneta, Puerto Rico
96km (60mi) NW of San Juan, Puerto Rico
arthquake overview : 2 moderate shallow earthquakes occurred at 2 AM just out the western Puerto Rico coast. The earthquakes were also felt as weak shaking in the Dominican Republic.
Felt reports from the greater epicenter area – image courtesy USGS
Update 13:48 UTC : The Red Sismica Puerto Rico is mentioning a max. VI MMI recorded in Mayaguez (strong shaking). There are many reports of fallen objects like books, staues, hanging objects, etc. Many people mave mentioned a loud rumble. The Agencia Estatal para el Manejo de Emergencias y Administración de Desastres (AEMEAD) has reported that no serious damage has occurred.
Update : The earthquake was also felt in the Dominican Republic.
Update : Since the first quake a number of aftershocks have been registered and we expect more to come
Update : NO damage has been reported so far. We will have to wait until daylight before this can be confirmed
Update : Max. intensity as reported by people near the epicenter was V (moderate shaking).
Update : The earthquakes were very well felt by the people living all over the island of Puerto Rico
Update : people living at the western coast close to the epicenter had the impression that the quakes were more dangerous than measured.
Update : Luckily the epicenter was not below land, but approx. 20 km out in the Mona passage.
The arrows in the map above show the direction the underlying Caribbean tectonic plates are moving, with the resultant build-up of pressure releasing into a myrid of earthquakes in the region over the years. Puerto Rico is the smaller green island in the middle, with the Dominican Republic the larger island to the left. The string of other Caribbean islands is buried under the earthquake markers that flow down the page to the lower right.
You can see the Puerto Rico Trench wraps around the entire zone.
A few little known facts came to the fore as I was researching this area after spotting the recent increase in seismic activity in the Caribbean region.
1. The Puerto Rico Trench is the biggest and deepest such trench in the entire Atlantic ocean.
2. This trench is capable of producing 8.0 earthquakes and above.
3. The risk of a major quake, underwater landslide and mega tsunami are as great as that of the Seattle area. In fact, one recent risk assessment put it at 35 to 55%!
4. The zone hasn’t ruptured in over 200 years and that has geologists seriously concerned.