USGS says the quake was 6.9 kilometers (4.2 miles) deep and hit around 11:42 a.m. PT.

About 100,000 people received an advanced notification from the Earthquake Warning California app.

“Advance notice varied from two seconds for those very near the epicenter to 18 seconds for those in the San Francisco,” Ferguson said.

Preliminary reports do not indicate any significant damage or injuries, the emergency services office told CNN.

Dr. Annemarie Baltay, a USGS seismologist, said Tuesday “there could be 10-15 aftershocks of magnitude 3 or greater in the next week.”

“Aftershocks of this magnitude and duration are totally normal for an event of this type,” she said. “If you do feel shaking don’t forget to drop, cover and hold on.”

The USGS did report another earthquake Tuesday.

This time a 3.6 magnitude that struck around 3:08 p.m. PT. Preliminary information from USGS shows the earthquake was 7.2 kilometers (4.5 miles) deep.