More than 400 small earthquakes have hit a section of Southern California over the last few days.
Residents in the area have felt rattled. But experts don’t expect major seismic activity from the recent activity concentrated in the Riverside County community of Glen Avon that they are calling the Glen Avon Earthquake Swarm.
“Swarms of small magnitude events are relatively common in this area, extending from Riverside to Chino,” the Southern California Seismic Network said in a report. “Based on past historic recordings this swarm is only expected to generate events of magnitude less than 4.0.”
The network, a project by Caltech and the U.S. Geological Survey, said the area where the quakes have occurred has “no major mapped fault but relatively abundant small seismicity indicating a local network of small fractures and faults. Earthquakes in this area are probably related to the tectonic loading of the nearby San Jacinto and San Andreas faults.”
Most of the quakes have been below magnitude 3.0 and were not noticed by residents. But several have been felt.
“Recently, it’s been like a roller coaster. Like, I was minding my own business, and then the earth is like shaking and I don’t know what’s … going on,” resident Viriginia Hidalgo told KCBS-TV.
“It’s nonstop. They think I’m crazy. My husband is like, ‘You’re crazy. It’s a truck that’s passing by.’ No, it’s not a truck,” Joanna Lopez told KABC-TV.
It has been almost five years since California experienced its last earthquake of magnitude 6 or stronger. Scientists say this calm period will end, and they give warnings about seismic dangers ranging from the Big One on the San Andreas fault to catastrophes that could come from lesser-known faults, such as the Hayward or Newport-Inglewood.
Researchers also recently discovered that the state has experienced 10 times more earthquakes than previously known. They documented 1.8 million earthquakes in Southern California over the last decade, the vast majority so small that they had been undetectable to computing systems. Previously, only 180,000 earthquakes were on record for the last 10 years.
Scientists are now better able to identify previously undiscovered faults, detect patterns of moving earthquake swarms — like the one in Riverside County — and identify faint clusters of foreshocks that occur before a larger earthquake.