Experts weigh in on earthquake swarms as shaking continues south of Salton Sea
BRAWLEY, Calif. (KESQ) – A large cluster of earthquakes centered in the Brawley area, south of the Salton Sea, continued to shake this week.
Well over 350 earthquakes have rattled the area since the weekend, though many of them have been microquakes – typically under magnitude 2.0. In just the past 24 hours, nearly two dozen of these types of temblors have been quietly rumbling under Brawley, as seen below.
A few of the quakes, though, have been on the larger side. A magnitude 4.5 quake struck on Saturday night, with a magnitude 4.7 one just after midnight on Sunday. The United States Geological Survey (USGS) provided an aftershock forecast after those two larger quakes, found here.
There's a difference between mainshock-aftershock earthquakes and earthquake swarms. "In a swarm, there's no obvious main shock. It doesn't necessarily decay the way we expect an aftershock sequence to decay," said an expert with the agency.
The quakes so far have been centered in between two major fault lines: the infamous San Andreas Fault and the Imperial Fault Zone. That area is referred to as the Brawley Seismic Area on fault maps published by the California Department of Conservation. Experts told News Channel 3 that the swarm activity has been decaying since the swarm started over the weekend, and even though there is a nonzero chance seismic activity in that area could jump to the San Andreas Fault, that chance remains low.
"The interesting thing about this swarm and many of the swarms in the Brawley areas, they actually go perpendicular to [those two faults]. So there may be almost more structure that might connect between the two faults or really get to be a complication between the two faults," revealed Andy Michael, a geophysicist with the U.S. Geological Survey who has been tracking the latest swarm in Brawley.
"Whenever we see a swarm in this area, people want to raise the possibility that it could jump on to the San Andreas Fault and create a larger earthquake. Certainly, that's within the realm of possibility," he continued. "But again, the way that the swarm is decaying, we would think that any large future earthquakes due to the swarm are unlikely."
Experts believe the Brawley Seismic Zone is prone to these earthquake swarms due to its proximity to a lot of geothermal activity. Several volcanoes, like Salton Buttes, just a few kilometers to the north, are indicative of that.
"What we think causes the swarms, especially in an area like Brawley, where you have geothermal processes and we have geothermal energy being produced or actually fluids moving at depth," said Michael. "When these fluids move, they create stress or they lubricate faults. Both things can be happening. And then we get a lot of smaller earthquakes being released. So it's sort of a part of a normal process in that area."
Michael pointed to a series of swarms that produced a magnitude 5.4 earthquake in 2012. Regardless of how normal these swarms are, though, he said it's a good reminder on preparedness.
Meanwhile, News Channel 3 previously reported on how local preparedness groups used this cluster of quakes as a reminder for valley residents to stay prepared. You can find that report by clicking here.
"These swarms get our attention," said Michael. "People can expect to continue feeling some small earthquakes, but really the overall risk is something we have to live with all the time, so people should remember to be prepared."
