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Afternoon Earthquake Update for Puerto Rico - January 10, 2020

January 10, 2020

Aftershock Forecast and Scenarios

seismic stations
Photo (L-R) Jose Cancel of Puerto Rico Seismic Network (PRSN), Alena Leeds of USGS and Javier Santiago of PRSN install a temporary seismometer at Sabana Yeguas in southwestern Puerto Rico on Jan. 10, 2020.

Ongoing Research

USGS and Puerto Rico Seismic Network (PRSN) experts are on the ground today near the south coast of Puerto Rico, working quickly to install six sets of seismometers that will help seismologists better monitor earthquakes, document the strength of ground shaking, estimate potential earthquake damage, and forecast aftershocks. The seismometers -- solar-powered and ready to travel in suitcase-sized kits -- were sent from the USGS’ Albuquerque Seismological Laboratory to Puerto Rico on January 7, the same day a magnitude 6.4 earthquake struck the southwest part of the island, causing extensive damage.

The temporary seismometers will supplement information on real-time earth movement already being collected by the PRSN, a permanent array of instruments in Puerto Rico and the Virgin Islands. USGS partners with the PRSN and the Puerto Rico Strong Motion Program at University of Puerto Rico Mayaguez to collect seismic data and monitor earthquakes in the region.

Aftershock Forecast

The forecast for Jan. 10 indicates the likelihood of large magnitude aftershocks continues to decrease as we move further away from the Jan. 7, 2020, M 6.4 earthquake. Over the next 7 days there is now only a 3 percent chance of one or more aftershocks larger than M 6.4. However, there is still a high likelihood of M 3.0+ aftershocks in the coming week; these M 3.0+ quakes may be felt near the epicenters. The rate of aftershocks will continue to decline over time. A large aftershock or new mainshock would, once again, increase the frequency and magnitude of aftershocks.

Since this series of events began in December 2019, more than 139 earthquakes M 3.0+ have occurred in this region, six of which were M 5.0+, including the largest M 6.4 event.

This earthquake sequence is consistent with expectations of seismicity in the region. Historically the region has seen moderate seismicity, but Puerto Rico is tectonically active, and infrequent naturally occurring large earthquakes are expected. Before this sequence, within the last 50 years and within 31 miles of the M 6.4 quake’s epicenter, there have been 10 earthquakes M 4.0+. Historical seismicity in the region can be searched here.

PR quakes
The figure above shows the distribution of seismicity southwest of Puerto Rico in December 2019 and January 2020. Earthquake symbols are sized by magnitude and colored according to the time of the earthquake relative to December 28, 2019. (Public domain.)

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