The first quake, which jolted residents just before 3:10 a.m., had a preliminary magnitude of 3.2 and was centered four miles south of Walnut Creek and 11 miles east-northeast of Oakland, according to the USGS.
The USGS said that the tremor had a depth of 5.3 miles.
A second earthquake with a preliminary magnitude of 2.4 was reported in the same location just before 3:20 a.m.
The aftershock had a depth of 4.1 miles, the USGS said.
Kristen Peters, Bay City News