Earthquake swarm rattles Calif., more than 100 quakes reported in 24 hours
A swarm of earthquakes, the largest a magnitude-4.9, rattled Southern California near the Mexico border Wednesday evening into Thursday morning. No damage or injuries were reported. More than 100 quakes of magnitude 2.5 and above have struck the remote Imperial County since 9 a.m. Thursday, according to the U.S. Geological Survey. Seismologist Lucy Jones said this is one of the largest swarms ever in the Imperial Valley - and this region historically sees the most active swarms in Southern California. The 4.9-magnitude temblor hit just after 5:30 p.m. and was centered about 2 1/2 miles northeast of Westmorland, a city of around 2,300 people near the Salton Sea, an inland desert lake. A 3.6-magnitude quake was reported five miles from Brawley, Calif. as recently as 7:46 a.m. Thursday. Jones said the quakes were in the Brawley seismic zone, where such swarms are common. It produced a magnitude-5.8 earthquake in 1981, Jones said in a tweet.
The zone is a network of small faults connecting the larger Imperial fault and the huge San Andreas fault. However, Jones said the current swarm was too far away to raise the low odds of affecting the San Andreas. "Today's M4.9 fault is ~2 miles across, so it can affect quakes within ~5 miles," Jones wrote on Twitter. "The only faults nearby are small. In other words, there is no scientific reason to predict a big quake in another location today." An average of 234 earthquakes with magnitudes between 3.0 and 4.0 occur per year in California and Nevada, according to a recent three-year data sample, the LA Times reported.
https://www.sfgate.com/bayarea/article/Earthquake-swarm-California-Imperial-Brawley-15612222.php