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A series of small earthquakes has rattled northern California, with over two dozen minor tremors detected within 30 miles of the San Andreas Fault in the past day. The strongest and most recent was a magnitude 2.7 quake that struck at 10:14 a.m. ET Monday morning in The Geysers, a large geothermal field north of San Francisco known for frequent swarms of tiny tremors.
According to the United States Geological Survey (USGS), these quakes ranged between 2.5 and 2.7 in magnitude, and no injuries, damage, or tsunami warnings have been reported. Seismic activity of this type, called an "earthquake swarm," involves a series of small quakes that occur over days, weeks, or even months, often without a single dominant main shock.
The USGS and the California Institute of Technology continue to monitor the situation, as swarms have also recently been recorded in areas like San Ramon. Many of these events are shallow, making them widely felt but causing no significant damage.
Experts say that while these swarms are common in regions with complex fault systems, they do not necessarily signal a major earthquake is about to happen. However, California remains at high risk for a significant seismic event, as scientists estimate a 72 percent chance that a magnitude 6.7 or greater earthquake will strike the broader Bay Area between now and 2043.
More than 70 percent of Californians live within 30 miles of a major fault, increasing the potential impact of even moderate seismic events. While geothermal energy production at The Geysers can sometimes trigger minor quakes, the most significant hazards remain tied to natural fault movement.
Seismic agencies advise residents to review emergency plans and expect additional aftershocks, as there is about a 5 percent chance of a larger earthquake occurring in the 72 hours following a moderate quake, according to USGS estimates. Monitoring will continue in the coming days as scientists work to better understand the ongoing seismic activity.