As of 3:27 a.m., there have been eight aftershocks since 2:41 a.m., the strongest being a measure 2.7.
BART is running 15-20 minute delays to inspect tracks for any possible earthquake damage.
Many people in the East Bay and as far south as San Jose say the quake woke them up.
There are no immediate reports of any damage.
@abc7newsBayArea felt it in south San Jose. My dog woke me up and then I felt a quick jolt. My dog is probably the best warning system yet!— Lorral_thebluecoat (@LorralWhaley) July 21, 2015
@abc7newsBayArea We felt it here in Downtown San Jose. One small shake followed by a slightly larger one.— rλan delucchi (@ryanonsrc) July 21, 2015
@abc7newsBayArea and peeps..don't forget to report that you felt it on the USGS site. Short survey.— mary b (@zukeferd) July 21, 2015
If you would like to report that you felt the initial measure 4.0 earthquake at 2:41 a.m., click here to report it to USGS.
If you see news where you live, tag your photos and videos on Twitter, Instagram, or Facebook with #abc7now.
Stay with ABC7News.com for the latest updates and tune into ABC7 News starting at 4 a.m. for live updates.
Prepare NorCal: Disaster preparedness resources