Magnitude 4.1 earthquake hits Northern California, prompts early warning

A magnitude 4.1 earthquake hit the southwest Sacramento County area Wednesday morning, close to Contra Costa, Solano and San Joaquin counties, the U.S. Geological Survey said.

The earthquake was reported at 9:29 a.m. and prompted an early warning, which was sent widely to cellphones across Northern California. The earthquake early warning system can send out alerts through the MyShake app, as well as through the Android operating system and an Amber Alert-style system; a test drill on the app is scheduled for Thursday at 10:19 a.m., on International ShakeOut Day.

Many people who live in the most highly populated areas of the San Francisco Bay Area and Sacramento area did not feel shaking from Monday’s earthquake. The strongest shaking, felt near the epicenter, was light, according to the U.S. Geological Survey, just enough to rattle dishes.

The preliminary epicenter in the southwestern tip of Sacramento County was about four miles southeast of Rio Vista, a city in eastern Solano County, and about 10 miles northeast of Oakley and 13 miles northeast of Antioch, which are in Contra Costa County.

In the past 10 days, there have been two earthquakes of magnitude 3.0 or greater centered nearby.

An average of 25 earthquakes with magnitudes between 4.0 and 5.0 occur per year in California and Nevada, according to a recent three year data sample.

The earthquake occurred at a depth of 6.7 miles. Did you feel this earthquake? Consider reporting what you felt to the USGS.

Find out what to do before, and during, an earthquake near you by signing up for our Unshaken newsletter, which breaks down emergency preparedness into bite-sized steps over six weeks. Learn more about earthquake kits, which apps you need, Lucy Jones’ most important advice and more at latimes.com/Unshaken.

A first draft of this story was automatically generated by Quakebot, a computer application that monitors the latest earthquakes detected by the USGS. A Times editor reviewed the post before it was published, then a Times staff writer updated the story. If you’re interested in learning more about the system, visit our list of frequently asked questions.