A series of nearly 300 earthquakes has struck under the desert town of Brawley near the Mexico border, 130 miles east of San Diego. The largest temblor measured magnitude 3.7.
The seismically active region connects the San Andreas and Imperial faults. Both are capable of major quakes, but the cluster of magnitude 3s and 2s is not necessarily a precursor to a big one, said geologist Pat Abbott, who lectures and leads field trips for the Smithsonian on all continents and oceans of the world.
The activity is more likely the continuation of tectonic plates pulling apart, he said.
"For 5-and-a-half million years, Baja California, San Diego are pulling away from Mexico and that is experienced with hundreds or thousands of earthquakes in these swarms in the warm rock in the Brawley area," Abbott explained.
"Do these small earthquakes lead to the big ones? Oh they might," he said. "You never know what day we’re going to have a big earthquake in California."
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Similar clusters of quakes hit near the region in September and October. The most recent large quake to strike Brawley was a magnitude 5.4 in 2012.
The last time the southern section of the San Andreas Fault ruptured was in 1680. Scientists estimate a big rupture usually occurs once every 150 or 200 years.
San Diego County is surrounded by several active faults capable of unleashing large quakes up to a magnitude 7 or higher, including the San Jacinto, Elsinore and offshore faults.
