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Southern California hit by earthquake swarms with largest measuring 4.9 magnitude, bigger quake 'less likely'

An expert said that the current quakes are near the 1981 Westmoreland earthquake, located in the seismically active Imperial Valley
(Getty Images)
(Getty Images)

A swarm of earthquakes has hit the south of the Salton Sea in the city of Westmoreland on September 30. It produced 240 earthquakes as of 8 pm Pacific Standard Time, with the largest measuring a magnitude of 4.9, according to the United States Geological Survey (USGS). The agency is monitoring the seismic activity in the area.

Westmoreland city sits in the Imperial Valley in Southeastern California. The current quakes are near the 1981 Westmoreland earthquake, located in the seismically active Imperial Valley, according to Dr. Lucy Jones, a seismologist at Dr. Lucy Jones Center. With a magnitude of 5.8, it severely damaged 12 buildings in the city back then.

"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," USGS Earthquakes tweeted

Screenshot of Latest Earthquakes showing the Westmoreland Earthquake Swarm beginning Sep 30, 2020. Earthquakes are shown as circles with the most recent in red.(Public domain.)

In just two and a half hours, the Westmoreland swarm has had 45 quakes of magnitude 3 and above. “One of the largest swarms we have had in the Imperial Valley – and it is historically the most active swarms in SoCal,” Dr Jones tweeted.


"Earthquake swarms in the Imperial Valley/Salton Trough are generally over within a few days," Zachary Ross, a seismologist, and assistant at Caltech tweeted. "The Imperial Valley has produced many swarms like this in the past. 2012 Brawley swarm, 2005 Obsidian Buttes, 1981 Westmoreland.

USGS has predicted some possibilities on how the swarms might evolve in the coming days. They predict that the earthquakes may continue but will decrease over the next 7 days. It is also possible that the region could witness earthquakes of magnitude 5.5 to 6.9 hitting but is less likely. A quake larger than a magnitude is the least likely outcome, they said.

The agency wants people to stay alert, especially when in or around vulnerable structures. "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," they wrote on their website. "When there are more earthquakes, the chance of a large earthquake is greater, which means that the chance of damage is greater."