A moderate earthquake struck Sonoma County on Sunday afternoon, setting off emergency alerts across Northern California and being felt as far south as San Francisco.
4.0 Magnitude Quake Shakes North Bay
According to the United States Geological Survey (USGS), a magnitude 4.0 earthquake occurred at around 3:30 p.m. on Sunday. The quake was centered near Glen Ellen in Sonoma County.
Residents in nearby areas, including Santa Rosa, reported gentle shaking. While there were no immediate reports of damage, the tremor was strong enough to get people’s attention.
Aftershocks Follow the Initial Earthquake
About 10 minutes after the main quake, a smaller 3.1 magnitude aftershock was recorded. Later, at 4:04 p.m., another earthquake measuring 3.4 magnitude struck near Kenwood.
These aftershocks are common following moderate earthquakes and usually decrease in strength over time.
Emergency Alerts Sent Across the Bay Area
Emergency earthquake alerts were sent to smartphones across a wide area, including San Francisco. Initially, the earthquake was estimated to be as strong as 4.9 magnitude, which explains why alerts were triggered.
Earthquake alerts are typically issued for quakes measuring 4.5 magnitude or higher. After further analysis, the USGS revised the quake’s strength first to 4.2 and then to 4.0.
Possible Fault Involved
The exact fault responsible for the earthquake has not yet been confirmed. However, the quake occurred near the Rodgers Creek Fault, which runs through central Sonoma County and under San Pablo Bay.
Under the bay, the Rodgers Creek Fault connects with the well-known Hayward Fault, one of the most active faults in the Bay Area.
Could This Be a Foreshock?
Many residents wonder whether a quake like this could be a warning sign of something larger.
The USGS estimates that any given earthquake has about a 5% chance of being followed by a stronger one within a week. Earthquakes that produce multiple aftershocks are slightly more likely to be foreshocks.
However, experts stress that a “larger quake” does not automatically mean a major disaster like the long-feared “Big One.” It simply refers to an earthquake stronger than the initial event.
Recent Earthquake Activity in the East Bay
Earlier in the weekend, shortly before 11 p.m. Saturday, two smaller earthquakes struck about 2 miles southeast of San Ramon in the East Bay. These quakes measured 2.8 and 2.7 magnitude and occurred at a depth of about 5 miles.
The San Ramon area has experienced dozens of small earthquakes in recent weeks. Seismologists say this kind of activity is common and usually does not signal a major earthquake.
Conclusion
The 4.0 earthquake in Sonoma County served as a reminder of Northern California’s active seismic landscape. While aftershocks followed and alerts reached much of the Bay Area, experts say there is no immediate indication of a major earthquake. Residents are encouraged to stay informed and review earthquake safety plans as seismic activity continues across the region.
