A swarm of earthquake activity is hitting the Salton Buttes area down in Southern California.
There have now been about 115 total quakes in this swarm since it got going in the middle of the night, though it technically started with a single one on Sunday afternoon.
The biggest quake was a M4.6 at 8:56 AM PDT on August 10, 2020. This is also the area’s biggest quake since 2012 when a similar swarm happened.
The numbers of quakes of different magnitudes are as follows:
- M4.0-4.9: 3
- M3.0-3.9: 11
- M2.0-2.9: 41
- rest being below M1.9
Quakes are occurring between 1-9 km below the Salton Sea.
This area, along with the Brawley Seismic Zone just to the south in the Imperial Valley, is prone to earthquake swarms.
There have been about three significant swarms in the past 20 years (2001, 2009, and 2016). The past swarms have remained active for 1 to 20 days, with an average duration of about a week.
The present one is certainly significant because of the size of the three biggest quakes so far, and its location just about 8 miles (12 km) from the southern end of the San Andreas Fault.
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.
Scenario One (Most likely, about 80% chance)
Earthquakes continue but none will be larger than M5.4 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 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, around 1% chance)
A much larger earthquake (M7.0 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.
So 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. So be ready!