San Francisco’s Next 'Big One' Could More Likely be 'Big ONES'

The San Francisco Bay Area’s next big seismic event could be another great quake like the infamous 1906 temblor, or perhaps more likely, the region could possibly be struck by a series of earthquakes, according to a new study published in the Bulletin of Seismological Society of America.

The Bay Area has a long seismic history, as its location straddles the both the northwest-moving Pacific Plate and the southeast-moving North American plate.

Stresses on these plates accumulate as their progress is impeded by their slow grind against each other.

Once built up to capacity, energy is released in the form of an earthquake along one of the area’s main faults.

While the San Andreas may be the most well known, several other faults are present and equally as dangerous: the Calaveras, Concord-Green Valley, Greenville, Hayward-Rodgers Creek and San Gregorio faults.
San Francisco Bay Area’s Earthquake History

Written earthquake history of the San Francisco Bay region began in 1776, when the Mission Dolores and the Presidio began keeping records of felt earthquakes and their ensuing damage.

This new study provides a window of insight of nearly 200 additional years worth of earthquakes, obtaining data from as early as the year 1600. Researchers created trenches across known faults to both observe previous recent surface ruptures as well as to date paleoearthquakes. They dated the ancient quakes by using radiocarbon dating of detrital charcoal and determining the presence of non-native pollen grains.

Researchers discovered that between 1690 and 1776, when record keeping began, that a cluster of earthquakes ranging from M6.6 to M7.8 occurred on the Calaveras fault (north segment), Hayward fault (north and south segments), Rodgers Creek fault, San Andreas fault (North Coast and San Juan Bautista segments) and the San Gregorio fault.

These earthquakes likely released an amount of energy equivalent to the release of the giant 1906 quake. DecodedScience