A magnitude 4.0 earthquake struck Sonoma County on Sunday afternoon, triggering emergency alerts across Northern California, including parts of San Francisco, according to the U.S. Geological Survey.
The quake hit at approximately 3:30 p.m. and was centered near Glen Ellen. Residents reported gentle shaking in Santa Rosa, and the initial tremor was followed by several aftershocks. About 10 minutes later, a 3.1-magnitude aftershock was recorded, followed by another quake measuring 3.4 near the Sonoma County community of Kenwood at 4:04 p.m.
Early readings initially estimated the quake at magnitude 4.9, which is strong enough to activate the state’s earthquake alert system. The magnitude was later revised to 4.2 and then downgraded to 4.0.
While the specific fault responsible has not been identified, the Rodgers Creek Fault runs through the area. That fault extends beneath San Pablo Bay, where it connects with the well-known Hayward Fault.
According to the USGS, earthquakes of this size generally carry about a 5% chance of being followed by a larger quake within a week. Events that produce multiple aftershocks are considered slightly more likely to be foreshocks, though a larger follow-up quake would not necessarily indicate a major seismic event.
Earlier in the weekend, two smaller earthquakes measuring 2.8 and 2.7 struck near San Ramon in the East Bay. That area has experienced dozens of minor quakes in recent weeks, a pattern experts say is typical and not usually a warning sign of a larger earthquake.
No damage or injuries related to Sunday’s quakes were immediately reported.
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