Salton Sea Earthquake Activity Returns to Normal Levels
Reduced activity for the swarm of earthquakes beneath the Salton Sea that began on August 10, 2020.
Last update: 08/14/2020 12pm Pacific
08/14/2020:
Over the past 5 days, we have been carefully monitoring the earthquake swarm in the Salton Sea. We are pleased to report that the earthquake activity has returned to typical pre-swarm levels. Since the swarm activity has subsided, we will no longer be updating this forecast; however, this does not mean the risk of a larger earthquake is gone. The southernmost section of the San Andreas Fault is capable of rupturing in large magnitude earthquakes (magnitude 7+), the last of which occurred more than 300 years ago. In a typical week, there is approximately a 1 in 10,000 chance of a magnitude 7+ earthquake on the southernmost San Andreas Fault. As noted below, the likelihood of a large earthquake has now returned to this typical long-term level. This swarm did not decrease the potential for a larger earthquake in the future and Southern California continues to be one of the most seismically active areas in the nation.
The earthquake swarm that began on August 10th continues to quiet down, producing no earthquakes of magnitude 2 and larger in the last 24 hours (as of noon August 14th). This is compared to a peak of 54 earthquakes on August 10th, the day of the M4.6 mainshock, which remains the largest earthquake so far. Our updated probabilities for the following three scenarios reflect this reduction in activity.
Historically, this area has seen swarms before – most recently in 2001, 2009, and 2016. During the last swarm in 2016, there were three bursts of activity separated by relatively quiet periods before the swarm ended. Past swarms in this area have remained active for 1 to 20 days, with a typical duration of about a week.
While the swarm appears to have died down for the moment, this area may have future bursts of activity that will impact the probabilities discussed below.
The following three scenarios describe possibilities of what could happen from 13 August to 21 August.
Only one of these scenarios will occur within the next week. These scenarios include the possibility of earthquakes on and off the San Andreas Fault.
- Scenario One (Most likely, about 99% chance): Earthquakes occur as normal, but none will be larger than magnitude 5.4 within the next 7 days.
Moderately sized earthquakes may occur (magnitude in the range M4.5-M5.4), which could cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M3.0+) may be felt by people close to the epicenters.
- Scenario Two (Less likely, about 1 in 1000 chance): A larger earthquake (magnitude 5.5 to 6.9) occurs within the next 7 days.
A less likely scenario is a somewhat larger earthquake (up to a M6.9). Earthquakes of this size could cause damage around the Salton Sea area and would be followed by additional aftershocks.
- Scenario Three (Least Likely, about 1 in 10,000 chance): A much larger earthquake (magnitude 7 or higher) occurs within the next 7 days.
A much less likely scenario, compared with the previous two scenarios, is a much larger earthquake (i.e., M7.0 and above). While this scenario has a very small probability of occurring, if such an earthquake were to occur, it would have serious impacts in the region and would be followed by its own aftershocks.
What people can do about earthquakes
The U.S. Geological Survey advises everyone to be aware of the possibility of future earthquakes, especially when in or around vulnerable structures such as unreinforced masonry buildings. This swarm may lead to larger and potentially damaging earthquakes in the future, so remember to: Drop, Cover, and Hold on if you feel shaking or receive a ShakeAlert message. When there are more earthquakes, the chance of a large earthquake is greater, which means that the chance of damage is greater.
Please refer to preparedness information provided by your local and state emergency management offices.
About our earthquake forecasts
No one can predict the exact time or place of any earthquake, including aftershocks or events in swarms. Our earthquake forecasts give us an understanding of the chances of having more earthquakes within a given time period in the affected area. We calculate this earthquake forecast using a statistical analysis based on past earthquakes.
One uncertain aspect of this swarm is whether there will be any additional bursts of activity. The chance of large earthquakes will again be elevated in any future swarm.
We are carefully monitoring activity throughout the region and will continue to provide information to help people stay safe and care for themselves and each other.
Earthquake Forecast for the Salton Sea Swarm of August 2020
08/13/2020:
Over the past 3 days, we have been carefully monitoring the Salton Sea for ongoing earthquake activity. The earthquake swarm that began on August 10th continues to quiet down, producing only 1 earthquake of magnitude 2 and larger in the last 24 hours (as of noon August 13th). This is compared to a peak of 54 earthquakes on August 10th, the day of the M4.6 mainshock, which remains the largest earthquake so far. Our updated probabilities for the following three scenarios reflect this reduction in activity; however, the risk of a large earthquake remains elevated due to the swarm when compared to background levels.
The southernmost section of the San Andreas Fault is capable of rupturing in large magnitude earthquakes (magnitude 7+), the last of which occurred more than 300 years ago. In a typical week, there is approximately a 1 in 10,000 chance of a magnitude 7+ earthquake on the southernmost San Andreas Fault. For the next week, we estimate an elevated chance of such an earthquake to be less than 1 in 1,000.
Historically, this area has seen swarms before – most recently in 2001, 2009, and 2016. During the last swarm in 2016, there were three bursts of activity separated by relatively quiet periods before the swarm ended. Past swarms in this area have remained active for 1 to 20 days, with a typical duration of about a week, so this swarm may have future bursts of activity that will in turn impact the probabilities discussed below.
The following three scenarios describe possibilities of what could happen from 13 August to 21 August.
Only one of these scenarios will occur within the next week. These scenarios include the possibility of earthquakes on and off the San Andreas Fault.
- Scenario One (Most likely, about 99% chance): Earthquakes continue but none will be larger than magnitude 5.4 within the next 7 days.
The most likely scenario is that the rate of earthquakes in the swarm will decrease over the next 7 days. Some moderately sized earthquakes may occur (magnitude in the range M4.5-M5.4), which could cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M3.0+) may be felt by people close to the epicenters.
- Scenario Two (Less likely, about 1% chance): A larger earthquake (magnitude 5.5 to 6.9) could occur within the next 7 days.
A less likely scenario is a somewhat larger earthquake (up to a M6.9). Earthquakes of this size could cause damage around the Salton Sea area and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
- Scenario Three (Least Likely, less than 1% chance): A much larger earthquake (magnitude 7 or higher) could occur within the next 7 days.
A much less likely scenario, compared with the previous two scenarios, is that the ongoing swarm could trigger an earthquake significantly larger than the M4.6 that occurred on the 10 August (i.e., M7.0 and above). While this is a very small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
08/12/2020:
Over the past 48 hours, we have been carefully monitoring the Salton Sea for ongoing earthquake activity. The earthquake swarm continues to quiet down, so far producing only 2 earthquakes of magnitude 2 and larger today (August 12th), compared to 54 on August 10th, the day of the M4.6 mainshock, which remains the largest earthquake so far, and 10 on August 11th. Our updated probabilities for the following three scenarios reflect this reduction in activity; however, the risk of a large earthquake is still considerably elevated due to the swarm when compared to background levels.
The southernmost section of the San Andreas Fault is capable of rupturing in large magnitude earthquakes (magnitude 7+), the last of which occurred more than 300 years ago. In a typical week, there is approximately a 1 in 10,000 chance of a magnitude 7+ earthquake on the southernmost San Andreas Fault. For the next week, we estimate an elevated chance of such an earthquake to be about 1 in 1,000.
Historically, this area has seen swarms before – most recently in 2001, 2009, and 2016. During the last swarm in 2016, there were three bursts of activity separated by relatively quiet periods before the swarm ended. Past swarms in this area have remained active for 1 to 20 days, with a typical duration of about a week, so this swarm may have future bursts of activity that will in turn impact the probabilities discussed below.
The following three scenarios describe possibilities of what could happen from 12 August to 20 August.
Only one of these scenarios will occur within the next week. These scenarios include the possibility of earthquakes on and off the San Andreas Fault.
- Scenario One (Most likely, about 99% chance): Earthquakes continue but none will be larger than magnitude 5.4 within the next 7 days.
The most likely scenario is that the rate of earthquakes in the swarm will decrease over the next 7 days. Some moderately sized earthquakes may occur (magnitude in the range M4.5-M5.4), which could cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M3.0+) may be felt by people close to the epicenters.
- Scenario Two (Less likely, about 1% chance): A larger earthquake (magnitude 5.5 to 6.9) could occur within the next 7 days.
A less likely scenario is a somewhat larger earthquake (up to a M6.9). Earthquakes of this size could cause damage around the Salton Sea area and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
- Scenario Three (Least Likely, less than 1% chance): A much larger earthquake (magnitude 7 or higher) could occur within the next 7 days.
A much less likely scenario, compared with the previous two scenarios, is that the ongoing swarm could trigger an earthquake significantly larger than the M4.6 that occurred on the 10 August (i.e., M7.0 and above). While this is a very small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
08/11/2020:
In the past 24 hours, we have been carefully monitoring the Salton Sea for ongoing earthquake activity. The earthquake swarm has quieted down relative to yesterday, so far producing only 10 earthquakes of magnitude 2 and larger today, compared to 54 yesterday, including the M4.6 mainshock on August 10, which is the largest earthquake so far. Our updated probabilities for the following three scenarios reflect this reduction in activity; however, the risk of a large earthquake is still considerably elevated due to the swarm when compared to background levels.
The southernmost section of the San Andreas Fault is capable of rupturing in large magnitude earthquakes (magnitude 7+), the last of which occurred more than 300 years ago. In a typical week, there is approximately a 1 in 10,000 chance of a magnitude 7+ earthquake on the southernmost San Andreas Fault. For the next week, we estimate an elevated chance of such an earthquake to be about 1 in 1,000.
Historically, this area has seen swarms before – most recently in 2001, 2009, and 2016. During the last swarm in 2016, there were three bursts of activity separated by relatively quiet periods before the swarm ended. Past swarms in this area have remained active for 1 to 20 days, with a typical duration of about a week, so this swarm may have future bursts of activity that will in turn impact the probabilities discussed below.
The following three scenarios describe possibilities of what could happen from 11 August to 19 August.
Only one of these scenarios will occur within the next week. These scenarios include the possibility of earthquakes on and off the San Andreas Fault.
- Scenario One (Most likely, about 98% chance): Earthquakes continue but none will be larger than magnitude 5.4 within the next 7 days.
The most likely scenario is that the rate of earthquakes in the swarm will decrease over the next 7 days. Some moderately sized earthquakes may occur (magnitude in the range M4.5-M5.4), which could cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M3.0+) may be felt by people close to the epicenters.
- Scenario Two (Less likely, about 2% chance): A larger earthquake (magnitude 5.5 to 6.9) could occur within the next 7 days.
A less likely scenario is a somewhat larger earthquake (up to a M6.9). Earthquakes of this size could cause damage around the Salton Sea area and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
- Scenario Three (Least Likely, less than 1% chance): A much larger earthquake (magnitude 7 or higher) could occur within the next 7 days.
A much less likely scenario, compared with the previous two scenarios, is that the ongoing swarm could trigger an earthquake significantly larger than the M4.6 that occurred on the 10 August (i.e., M7.0 and above). While this is a very small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
08/10/2020:
The largest earthquake that has occurred, as of this release, is a magnitude 4.6 at 8:56 AM PDT on August 10. This earthquake and the associated swarm are located approximately 8 miles from the southern end of the San Andreas Fault. This area has also seen swarms in the past – most recently, in 2001, 2009, and 2016. Past swarms have remained active for 1 to 20 days, with an average duration of about a week.
During this earthquake swarm, the probability of larger earthquakes in this region is significantly greater than usual. The southernmost section of the San Andreas Fault is capable of rupturing in large magnitude earthquakes (magnitude 7+), but the last earthquake that strong was more than 300 years ago. In a typical week, there is approximately a 1 in 10,000 chance of a magnitude 7+ earthquake on the southernmost San Andreas Fault. That probability is significantly elevated while swarm activity remains high.
The following three scenarios describe possibilities of what could happen from 10 August to 18 August.
Only one of these scenarios will occur within the next week. These scenarios include the possibility of earthquakes on and off the San Andreas Fault.
- Scenario One (Most likely, about 80% chance): Earthquakes continue but none will be larger than magnitude 5.4 within the next 7 days.
The most likely scenario is that the rate of earthquakes in the swarm will decrease over the next 7 days. Some moderately sized earthquakes may occur (magnitude in the range M4.5-M5.4), which could cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M3.0+) may be felt by people close to the epicenters.
- Scenario Two (Less likely, about 19% chance): A larger earthquake (magnitude 5.5 to 6.9) could occur within the next 7 days.
A less likely scenario is a somewhat larger earthquake (up to a M6.9). Earthquakes of this size could cause damage around the Salton Sea area and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
- Scenario Three (Least Likely, approximately 1% chance): A much larger earthquake (magnitude 7 or higher) could occur within the next 7 days.
A much less likely scenario, compared with the previous two scenarios, is that the ongoing swarm could trigger an earthquake significantly larger than the M4.6 that occurred on the 10 August (i.e., M7.0 and above). While this is a very small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
What people can do about earthquakes
The U.S. Geological Survey advises everyone to be aware of the possibility of future earthquakes, especially when in or around vulnerable structures such as unreinforced masonry buildings. This swarm may lead to larger and potentially damaging earthquakes in the future, so remember to: Drop, Cover, and Hold on if you feel shaking or receive a ShakeAlert message. When there are more earthquakes, the chance of a large earthquake is greater, which means that the chance of damage is greater.
Please refer to preparedness information provided by your local and state emergency management offices.
About our earthquake forecasts
No one can predict the exact time or place of any earthquake, including aftershocks or events in swarms. Our earthquake forecasts give us an understanding of the chances of having more earthquakes within a given time period in the affected area. We calculate this earthquake forecast using a statistical analysis based on past earthquakes.
One uncertain aspect of this swarm is how long the elevated earthquake activity will last. We include this uncertainty in swarm duration in our forecasts. The chance of large earthquakes will remain elevated as long as the swarm continues. About half of the swarms in this area are over within a week. We will update our forecast as swarm activity increases or decreases, or if larger earthquakes occur.
We are carefully monitoring activity throughout the region and will continue to provide information to help people stay safe and care for themselves and each other.
Updated forecasts will be released on the USGS Earthquake Hazard Program website.
For media inquires, please contact Paul Laustsen at plaustsen@usgs.gov.
For More Information
- What is the difference between aftershocks and swarms?
- Earthquake Preparedness (Cal OES - California Governor's Office of Emergency Services)
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