A small but noticeable 3.6-magnitude earthquake happened Thursday at 12:41 pm, with an epicenter two miles southeast of Vallejo.
According to the US Geological Survey, a 3.6M earthquake rumbled just south of Vallejo Thursday afternoon, and miled shaking was felt in San Francisco, the East Bay, and parts of the North Bay.
The earthquake appears to have occurred along the Southampton Fault, which appears like a northern extension of the Calaveras Fault — a fault running under the East Bay and down to Hollister, just east of the Hayward Fault.
A swarm of small earthquakes along the Calaveras Fault occurred on Sunday morning, as the Chronicle reported, with the largest being 3.8M. The fault is thought to be capable of producing quakes as big as 6.7M, or thereabouts.
A map below shows the major and minor faults under the Bay Area, with the Southampton Fault appearing in yellow, labeled with the number 11. It crosses paths with the Franklin Fault, which leads directly out of the Calaveras Fault and under the city of Vallejo.
Connected faults are believed to be able to erupt together, potentially causing larger earthquakes. A study from almost a decade ago found that the Rodgers Creek and Hayward faults are interconnected, capable of causing a quake along a stretch that extends 115 total miles.
Map via USGS
