San Francisco has been shaken by a series of small earthquakes over 24 hours in California – the US state where a ‘Big One’ could happen at any moment. Friday’s seismic sequence began at 2:32 a.m., with a magnitude 2.7 temblor, followed by a magnitude 2.8 earthquake less than an hour later. A magnitude 3.3 earthquake hit at 5:28 a.m. The BART train service delayed trains after the magnitude 3 earthquakes Friday as a safety precaution.
Earthquake swarms like the one that began on Feb. 16 in the Danville area have been common over the past few decades, occurring in 1970, 1976, 1990, 2002, 2003 and 2015. They occur in the San Ramon Valley corridor along Interstate 680 between Walnut Creek and the Dublin and Pleasanton areas, said U.S. Geological Survey research geologist Belle Philibosian.