The Hayward fault has had a couple of jolts in recent days. The southern San Andreas had several events in the past few days.
https://www.chicagotribune.com/91619408-132.html
Seismologists are worried the recent earthquake swarm at the Salton Sea will temporarily increase the likelihood of a major quake in Southern California.
CBS in San Francisco:
PIEDMONT (CBS SF) — Mother Nature jolted East Bay residents out of their beds for a second straight day as a 3.5 magnitude earthquake struck the Hayward Fault near Piedmont, authorities said.
According to the U.S. Geological Survey, the temblor struck at 6:11 a.m. 3 miles north of Piedmont. Nearly in the same spot as Wednesday’s 3.4 magnitude quake that struck near Tunnel Road and Highway 13.
The quake was felt most strongly in Berkeley and Oakland, but residents in San Francisco also reported a strong jolt.
Map of magnitude 3.5 earthquake that struck near Piedmont on January 17, 2019. (USGS)
BART shut down trains for a short time to inspect its tracks for damage. The transit agency said to expect 10-20 minute delays.
There were no reports of injuries of damage.
On the KPIX 5 Facebook page, several local residents said the quake jolted them awake.