The Southern California/ Mexico Border region was shaken by a swarm of earthquakes in the Imperial Valley on Wednesday afternoon, according to the U.S. Geological Survey (USGS).
The quakes started around 4:45 p.m. northeast of Westmorland near Brawley, with the largest quake, a 4.9 magnitude, occurring at 5:51 p.m., the USGS said.
That quake was felt as far as Oceanside and Tijuana, according to the USGS.
The quakes have, so far, ranging from magnitude 2.5 to 4.9.
According to USGS here is what may be reasonable to expected:
1. Scenario One (Most likely): Earthquakes continue, possibly including earthquakes up to magnitude 5.4.
The most likely scenario is that the rate of earthquakes in the swarm will decrease over the next 7 days. Some additional moderately sized earthquakes (M4.5 to 5.4) may occur, which could cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M3.0+) may be felt by people close to the epicenters.
2. Scenario Two (Less likely): 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 could occur (up to a M6.9). Earthquakes of this size could cause damage around the area close to the earthquakes that have already occurred and would be followed by aftershocks that would increase the number of smaller earthquakes per day. This scenario occurred in a previous swarm in the area – in 1981, when a swarm in this region included a magnitude 5.8 earthquake.
3. Scenario Three (Least Likely): 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 M4.9 that occurred on the 30 September (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 an earthquake alert powered by the ShakeAlert earthquake early warning system. When there are more earthquakes, the chance of a large earthquake is greater, which means that the chance of damage is greater.
Earthquakes like they happened today usually won’t cause injuries or much damages, but earthquakes 7 or larger could become devastating.
The largest earthquake that has occurred, as of this release, is a magnitude 4.9 at 5:31 PM PDT. This earthquake and the associated swarm are located in an area of diffuse seismic activity between the San Andreas fault in the north and the Imperial fault to the south. This area has also seen swarms in the past –notably the 1981 Westmorland swarm, which included a M5.8 earthquake, and the 2012 Brawley swarm, which included a M5.4 earthquake. Past swarms have remained active for 1 to 20 days, with an average duration of about a week. The current swarm is occurring about 40 kilometers (25 miles) to the south of the swarm that occurred near Bombay Beach in August 2020.
In a typical week, there is approximately a 3 in 10,000 chance of a magnitude 7+ earthquake in the vicinity of this swarm. During this earthquake swarm, the probability of larger earthquakes in this region is significantly greater than usual. Currently, the swarm is rapidly evolving, and we expect to update this forecast with more specific probability information as we collect more data.
