[USGS] 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.
