A magnitude 4.2 earthquake struck Northern California on Wednesday, October 18, 2023, triggering the ShakeAlert early warning system in the Bay Area. The quake struck at 9:29 a.m. about 2 miles south-southwest of Isleton, a small town in Sacramento County, according to the U.S. Geological Survey (USGS). It was felt in Sacramento, Stockton, and other parts of the Central Valley, as well as in the Bay Area cities of San Francisco, Oakland, and Berkeley.
The ShakeAlert system detected the earthquake’s seismic waves and sent out alerts to smartphones and other devices in the Bay Area, giving people a few seconds to take cover before the shaking arrived. This is the first time that the ShakeAlert system has been triggered for an earthquake in the Bay Area.
There were no immediate reports of damage from the earthquake. However, some people reported feeling the shaking and hearing a loud boom.
Earthquakes are common in California, and the Bay Area is particularly vulnerable to large earthquakes. The San Andreas Fault, which runs through the Bay Area, is capable of producing a magnitude 7.9 earthquake or larger.
The ShakeAlert system is an important tool for early warning of earthquakes. It can give people precious seconds to take cover before the shaking arrives, which can help to reduce injuries and save lives.
What to do during an earthquake
If you are in an earthquake, the best thing to do is to drop, cover, and hold on. Drop to the ground, cover your head and neck with your arms, and hold on to a sturdy object until the shaking stops. If you are indoors, get under a table or desk. If you are outdoors, find a clear spot away from buildings, trees, and power lines.
After the earthquake, be aware of the possibility of aftershocks. Continue to monitor the news and follow the instructions of local officials.