Per USGS:
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.