Magnitude 6.4 Earthquake in Puerto Rico

Release Date:

Links to forecasts and scenerios (below) will continue to be updated, however, text in this story will not be updated unless there is significant change to the aftershock behavior or to the USGS response to the earthquake. 

7-day aftershock forecast [English]

30-day aftershock scenarios [English | Spanish]

Update - Wednesday, January 29 (in English; Spanish below)

click on image for full description

2020 Southwest Puerto Rico Earthquake Sequence

In a new report released today, USGS experts estimated that aftershocks from the magnitude 6.4 Jan. 7, 2020, earthquake will persist for years to decades, although with decreasing frequency. Additionally, earthquakes will likely be felt on a daily basis for several more months.

The forecasts found in this report can be used to guide public policy decisions or other actions.

The report forecasts aftershock duration potential for up to ten years after the magnitude 6.4 mainshock in southwestern Puerto Rico. This sequence is very active, and the probabilities of magnitude 5 and 6 or greater aftershocks remain high now and into the future. More detailed findings are in bullets below.

Puerto Rico lies in a tectonically active region where earthquakes have occurred for centuries, but because Puerto Rico has not experienced a quake of this level of impact since 1918, the recent quakes, their aftershocks, and resulting damage took many islanders by surprise. About 7,500 people have left their homes for other kinds of shelter, including, in some cases, cars and tents.

“Puerto Rico’s recent large earthquake and its aftershocks were destructive and unsettling to people on the island,” said USGS Director Jim Reilly. “USGS and our partners at the Puerto Rico Seismic Network began deploying additional seismic stations shortly after the mainshock. We will continue to work diligently to provide timely earthquake information -- such as this aftershock duration report -- to help support and protect the local communities of our nation.”

The study results do not imply a change in the risk of earthquakes in other parts of Puerto Rico. The results in this report are based on the current behavior (as of January 17, 2020) of this aftershock sequence and may need to be modified if that behavior changes, including if a larger earthquake occurs.

Key findings of the report include:

  • People in the area affected by the aftershocks may feel shaking from magnitude 3 aftershocks on a daily basis for the next 2 to 6 months. The rate of aftershocks is expected to decline, but they may still feel such shaking on a weekly basis for between 1.5 years and a decade.
  • The annual chance of having one or more magnitude 5 or greater aftershock will remain above  25 percent for up to a decade or more.
  • The annual chance of a magnitude 6 or greater aftershock will remain above 25 percent for 3 months to 3 years.
  • Within the next year, there is a 20-30 percent chance of an aftershock as large as the mainshock or larger.
  • Within the next year, there is a 5-10 percent chance of a magnitude 7 or greater earthquake.
  • Future aftershocks are likely to be located where aftershocks have already been occurring -- within about 30 kilometers (about 20 miles) of the epicenter of the magnitude 6.4 mainshock.
  • The aftershocks discussed in this report would be located in the same general area as the aftershocks that have already occurred. Our results do not imply a change in the risk of earthquakes in other parts of Puerto Rico.
  • Changes in the behavior of the aftershock sequence, including the occurrence of a new large aftershock, could require new estimates.

 

click on image for full description

Informe sobre los terremotos del 2020 en Puerto Rico.

¿Qué hacer después de un terremoto?

En un nuevo informe publicado hoy, los expertos del USGS estimaron que las réplicas del terremoto de magnitud 6.4 del 7 de enero de 2020 persistirán durante años o décadas, aunque con una frecuencia decreciente. Además, los terremotos probablemente se sentirán a diario durante varios meses más.

Los pronósticos que se encuentran en este informe se pueden usar como guía para lo toma de decisiones de política pública u otras acciones.

El informe pronostica un potencial de duración de las réplicas de hasta diez años después del de magnitud 6.4 en el suroeste de Puerto Rico. Esta secuencia es muy activa, y las probabilidades de réplicas de magnitud 5 y 6 o mayores permanecen altas ahora y en el futuro. Los hallazgos más detallados están listados a continuación.

Puerto Rico se encuentra en una región tectónicamente activa donde los terremotos han ocurrido durante siglos, pero debido a que Puerto Rico no ha experimentado un terremoto de este nivel de impacto desde el 1918, los terremotos recientes, sus réplicas y el daño resultante tomaron por sorpresa a muchos isleños. Unas 7,500 personas han abandonado sus hogares para buscar otro tipo de refugio incluidos, en algunos casos, automóviles y tiendas de campaña.

"El reciente gran terremoto de Puerto Rico y sus réplicas fueron destructivas e inquietantes para la gente en la isla", dijo el director del USGS Jim Reilly. “El USGS y nuestros colaboradores en la Red Sísmica de Puerto Rico comenzaron a instalar estaciones sísmicas adicionales poco después del terremoto principal. Continuaremos trabajando diligentemente para proporcionar información oportuna sobre terremotos, como este informe de duración de réplicas, para ayudar a apoyar y proteger a las comunidades locales de nuestra nación".

Los resultados del estudio no implican un cambio en el riesgo de terremotos en otras partes de Puerto Rico. Los resultados en este informe se basan en el comportamiento actual (a partir del 17 de enero de 2020) de esta secuencia de réplicas y es posible que deba modificarse si ese comportamiento cambia, incluso si ocurre un terremoto más grande.

Los hallazgos más importantes del informe incluyen:

  • Las personas en el área afectada por las réplicas pueden sentir diariamente temblores de magnitud 3 durante los próximos 2 a 6 meses. Se espera que la tasa de réplicas disminuya, pero aún pueden sentir tales temblores semanalmente entre 1.5 años y una década.
  • La probabilidad anual de tener una o más réplicas de magnitud 5 o mayor se mantendrá por encima del 25 por ciento durante una década o más.
  • La probabilidad anual de una réplica de magnitud 6 o mayor se mantendrá por encima del 25 por ciento durante 3 meses a 3 años.
  • Dentro del próximo año, hay una probabilidad del 20-30 por ciento de una réplica tan grande como la principal o mayor.
  • Dentro del próximo año, hay una probabilidad del 5-10 por ciento de un terremoto de magnitud 7 o mayor.
  • Es probable que las réplicas futuras se ubiquen donde ya se han producido réplicas, dentro de unos 30 kilómetros (aproximadamente 20 millas) del epicentro del terremoto principal de magnitud 6.4.
  • Las réplicas discutidas en este informe se ubicarían en la misma área general que las réplicas que ya han ocurrido. Nuestros resultados no implican un cambio en el riesgo de terremotos en otras partes de Puerto Rico.
  • Los cambios en el comportamiento de la secuencia de réplicas, incluida la aparición de una nueva réplica grande, podrían requerir nuevos estimados.

Evening Update - Friday, January 17 (**Last routine update**)

New Top Story: As Aftershocks Continue in Puerto Rico, USGS Supports Quake Recovery 

Video Transcript

[Video] Scientists map the ground failure that occurred due to the Puerto Rico.

Steve Sobieszczyk, USGS (Public domain.)

7-Day Aftershock Forecast

The USGS aftershock forecast indicates there is a 3 percent chance of a magnitude 6.4 or larger aftershock over the next 7 days.

30-Day Aftershock Scenarios (Revised: Jan 17; English | Spanish)

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 18 to February 18, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely): 79 percent chance [same as yesterday]

click on image for full description

2020 Puerto Rico Earthquake Sequence

Earthquakes detected between December 28, 2019 as of January 16, 2020. Subject to updates.(Public domain.)

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Scenario Two (less likely): 18 percent chance [same as yesterday]

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  3 percent chance [same as yesterday]

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

click on image for full description

Secuencia del Terremoto en Puerto Rico, 2020

Terremotos detectados entre diciembre 28, 2019 hasta enero 16, 2020. Sujeto a actualizaciones.(Public domain.)

 

Evening Update - Thursday, January 16

7-Day Aftershock Forecast

The USGS aftershock forecast indicates there is a 3 percent chance of a magnitude 6.4 or larger aftershock over the next 7 days.

30-Day Aftershock Scenarios (Revised: Jan 16; English | Spanish)

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 17 to February 17, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely): 79 percent chance [same as yesterday]

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Scenario Two (less likely): 18 percent chance [same as yesterday]

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  3 percent chance [same as yesterday]

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

 

 

 

Evening Update - Wednesday, January 15

Video Transcript

Dr. Elizabeth Vanacore talks about the installation of temporary seismic stations in southwest Puerto Rico.

Donyelle Davis, USGS

(Public domain.)

7-Day Aftershock Forecast

The USGS aftershock forecast indicates there is a 4 percent chance of a magnitude 6.4 or larger aftershock over the next 7 days.

30-Day Aftershock Scenarios (Revised: Jan 15; English | Spanish)

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 16 to February 16, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely): 79 percent chance [same as yesterday]

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Three people looking at instrumentation

USGS scientists Thomas L. Pratt and Alena L. Leads, along with Dr. Elizabeth Vanacore, associate research professor at University of Puerto Rico, analyze data in earthquake monitoring and recording equipment amid aftershocks across the island's southern coast.

(Credit: Donyelle Davis, USGS. Public domain.)

Scenario Two (less likely): 18 percent chance [same as yesterday]

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  3 percent chance [same as yesterday]

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

 

Evening Update - Tuesday, January 14

7-Day Aftershock Forecast

The USGS aftershock forecast indicates there is a 3% chance of a magnitude 6.4 or larger aftershock over the next 7 days.

30-Day Aftershock Scenarios (Revised: Jan 14; English | Spanish)

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 14 to February 14, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely): 79 percent chance [-2% from yesterday]

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Scenario Two (less likely): 18 percent chance [+1% from yesterday]

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  3 percent chance [+1% from yesterday]

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

 

Evening Update - Monday, January 13

7-Day Aftershock Forecast

The USGS aftershock forecast indicates there is a 3% chance of a magnitude 6.4 or larger aftershock over the next 7 days.

 

30-Day Aftershock Scenarios (Revised: Jan 13; English | Spanish)

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 13 to February 13, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely): 81 percent chance [+5% from yesterday]

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Scenario Two (less likely): 17 percent chance [-4% from yesterday]

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  2 percent chance [-1% from yesterday]

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

 

Morning Update - Monday, January 13

Aftershock Forecast

The USGS aftershock forecast, updated on Jan. 13, indicates the likelihood of a M 6.0 or larger aftershock over the next 7 days is 8 percent [down 3% from yesterday]. There continues to be a high likelihood of M 3.0+ aftershocks this week. The rate of aftershocks will continue to decline over time. 

Estimates for other magnitude ranges and time periods can be found in the forecast.

 

30-Day Aftershock Scenarios (Revised: Jan 13; English | Spanish)

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 13 to February 13, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely): 81 percent chance [+5% from yesterday]

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Scenario Two (less likely): 16 percent chance [-5% from yesterday]

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  3 percent chance [0% from yesterday]

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

 

Puerto Rico Earthquake Update - Sunday, January 12

Aftershock Forecast

The USGS aftershock forecast, updated on Jan. 12, indicates the likelihood of a M 6.0 or larger aftershock over the next 7 days is 11 percent. There is also 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. Estimates for other magnitude ranges and time periods can be found in the forecast.

 

30-Day Aftershock Scenarios (Revised: Jan 12; EnglishSpanish)

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 12 to February 12, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely): 76 percent chance

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Scenario Two (less likely): 21 percent chance

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  3 percent chance

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

 

Morning Update on January 11

Aftershock Forecast

The USGS aftershock forecast, updated on Jan. 11, indicates the likelihood of a M 6.0 or larger aftershock over the next 7 days is 12 percent. There is also 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.  Estimates for other magnitude ranges and time periods can be found in the forecast.

 

30-Day Aftershock Scenarios (Revised: Jan 11; Spanish-language version)

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 11 to February 11, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely):  75 percent within the next 30 days

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Scenario Two (less likely): 22 percent within the next 30 days

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  3 percent within the next 30 days

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

 

Afternoon Update on January 10

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.

(Credit: Thomas Pratt, USGS. Public domain.)

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.

View the USGS aftershock forecast 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.)

Afternoon Update on January 9

Damaging earthquakes, like the ones in Puerto Rico, can be unsettling, destructive, and often tragic to the communities they affect. This is why the USGS continues to work diligently toward improving public safety by providing emergency responders and others with the scientific resources they need to better respond to ongoing hazards.

Here is the latest aftershock forecast for the M 6.4 that occurred January 7, 2020.

About Aftershock Scenarios

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 9 to February 9, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely):  84 percent within the next 30 days

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

Scenario Two (less likely): 14 percent within the next 30 days

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  2 percent within the next 30 days

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

 

Afternoon Update on January 8

relative seismicity

Timeline of recent earthquake sequence in Puerto Rico during December 2019 (weeks 49-52) and early January 2020 (weeks 1-2). Each symbol represents an earthquake sized by magnitude.

(Public domain.)

Aftershock Forecast

Today's forecast [as of 03:24:26 EST] estimates that over the next 1 Week there is a 4 percent chance of one or more aftershocks that are larger than magnitude 6.4. It is highly likely that there will be many smaller earthquakes (M>3) over the next 1 Week. Magnitude 3 and above events are large enough to be felt near the epicenter. The rate of aftershocks will decline over time, but a large aftershock can increase the numbers again, temporarily.

Our forecasts change as time passes due to decline in the frequency of aftershocks, larger aftershocks that may trigger further earthquakes, and changes in forecast modeling based on the data collected for this earthquake sequence.

 

Afternoon Update on January 7

The USGS National Earthquake Information Center is preparing to deploy six portable seismometers to Puerto Rico to supplement the seismometers already part of the Puerto Rico Seismic Network. These seismometers, which will be used to help better monitor earthquakes in this area, may be operational by the end of this week. Observations from seismic monitoring equipment will improve our ability to characterize and forecast earthquakes which will help protect lives and property. USGS works in partnership 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.

"After the devastating Hurricane Maria occurred in Puerto Rico, the federal government invested in rebuilding damaged seismic stations in the region," said USGS Director Jim Reilly. “These stations have made it possible for the USGS and our partners at the Puerto Rico Seismic Network to provide more accurate and rapid information about the earthquakes and their possible impacts along with better forecasts of potentially damaging aftershocks.”

Since the M 4.7 event on December 28, 2019, over 500 M 2+ earthquakes have occurred in this region (as of 2PM EST, 01/07/20), 32 of which were M 4+, including the January 6th M 5.8 and the M 6.4 event on January 7th and its aftershocks.

Aftershock Forecast

Earthquake forecasts are created using a statistical analysis based on past earthquakes and are presented in terms of probabilities of earthquakes of a given size occurring. The current forecast, issued at 15:24 eastern on Jan 7, 2020, estimates that over the next 1 Week there is a 7 percent chance of one or more aftershocks that are larger than magnitude 6.4. It is highly likely that there will be many smaller earthquakes (M>3) over the next 1 Week. Magnitude 3 and above events are large enough to be felt near the epicenter. The rate of aftershocks will decline over time, but a large aftershock can increase the numbers again, temporarily. This forecast may change as the earthquake sequence continues to develop.

Portable Seismic Station

Two portable sensors: a strong motion sensor (to record strong shaking that can be felt) and a broadband sensor (to record weak motion for detecting small earthquakes) buried into the ground to detect earthquakes. These stations can be quickly deployed and send real-time data back to the USGS via cellular telemetry immediately after they are installed. This photo was taken in Ridgecrest, CA.

(Public domain.)

Seismicity and seismic monitoring stations

The map above shows seismicity (orange circles) and seismic monitoring stations (triangles). Seismic stations that have been recently upgraded are emphasized in red.

(Public domain.)

Morning Update on January 7

On Jan. 7, a magnitude 6.4 earthquake struck the region at 4:24 am local time (08:24:26 UTC). Significant damage is possible. Over the past several weeks, hundreds of small earthquakes have occurred in the Puerto Rico region, beginning in earnest with a M 4.7 earthquake late on December 28 and a M 5.0 event a few hours.

The magnitude 6.4 earthquake was widely felt. According to ShakeMap, strong to very strong shaking occurred across parts of Southern Puerto Rico closest to the event and moderate shaking occurred across the rest of the island. The NOAA Tsunami Warning System states no tsunami warning or advisory. The USGS summary page on this earthquake includes an aftershock forecast. Aftershocks will continue near the mainshock. 

Over the past several weeks, hundreds of small earthquakes have occurred in this same region, beginning in earnest with a M 4.7 earthquake late on December 28 and a M 5.0 event a few hours later. Since the M 4.7 event, over 400 M 2+ earthquakes have occurred in this region, ten of which were M 4+, including today’s M 6.4 event and yesterday's 5.8 quake. The preliminary location of today's 6.4 earthquake is within about 7.5 miles (12 km) of the January 6, 2020, M 5.8 earthquake. The proximity of these events to Puerto Rico, and their shallow depth, mean that dozens of these events have been felt on land, though with the exception of the latest two earthquakes, the M 6.4 and the M 5.8, none are likely to have caused significant damage.

The January 6 and 7, 2020, M 5.8 and M 6.4 earthquakes offshore of southwest Puerto Rico occurred as the result of oblique strike slip faulting at shallow depth. At the location of this event, the North America plate converges with the Caribbean plate at a rate of about 20 mm/yr towards the west-southwest. The location and style of faulting for the event is consistent with an intraplate tectonic setting within the upper crust of the Caribbean plate, rather than on the plate boundary between the two plates.

Topography and bathymetry map of the Northeastern Caribbean.

Fault traces are shown as lines with the following descriptions: barbed=thrust fault; solid=strike-slip fault with arrows showing relative direction of motion; black and white=normal fault. Faults outlined in red have a potential to generate a large earthquake. The arrow at the top right corner shows the direction of the North American plate motion relative to the Caribbean plate. All red stars with a date before the 20th century show the intensity center (MI) for that earthquake. The red star with a red ellipse shows the general location of several 17th century earthquakes with sparse felt data. Stars with 20th and 21st century years are earthquake epicenters located using instrument data. Years in boxes next to red outlines are reoccurrence rates. Red question marks indicate unknown reoccurrence rates for those respective faults. Those parts of the subduction zone not outlined by red are not expected to generate large earthquakes

(Public domain.)

Tectonics in Puerto Rico are dominated by the convergence between the North America and Caribbean plates, with the island being squeezed between the two. To the north of Puerto Rico, North America subducts beneath the Caribbean plate along the Puerto Rico trench. To the south of the island, and south of today’s earthquake, Caribbean plate upper crust subducts beneath Puerto Rico at the Muertos Trough. The January 6 earthquake, and other recent nearby events, are occurring in the offshore deformation zone bound by the Punta Montalva Fault on land and the Guayanilla Canyon offshore.

Visit the USGS event page for more information. For estimates of casualties and damage, visit the USGS Prompt Assessment of Global Earthquakes for Response (PAGER) website. If you felt any of these earthquakes, report your experience on the “USGS Did You Feel It?” website for this event.

USGS scientists expect that this event will trigger aftershocks, but these will decrease in frequency over time. You can view the aftershock forecast here.

The USGS operates a 24/7 National Earthquake Information Center in Colorado that can be reached for more information at 303-273-8500. Learn more about the USGS Earthquake Hazards Program.