Napa Earthquake and Future Earthquakes in Northern California

The figure below from the Bill Ellsworth at the USGS is a depiction of the earthquake history of Northern California up to about 1990.  In the Bay Area, the last earthquake of significance was the magnitude ~6.9 Loma Prieta earthquake of October 17, 1989.  Last sunday's magnitude 6 Napa earthquake was in fact the strongest earthquake north of San Francisco and south of Eureka  since 1906. 

In terms of earthquake history, there was an earthquake similar to Loma Prieta in June 1838, about magnitude 6.8.  30 years later, on October 21, 1868, the magnitude ~6.9 Hayward fault earthquake occurred, rupturing the southern end of the fault.  It was known as the “great San Francisco earthquake” prior to 1906. 

Both of these events were part of the run-up to the 1906 San Francisco earthquake.  One of the other events was the 1892 magnitude 6.4 Vacaville-Winters earthquake on the Berryessa fault, just to the east of Napa.

With respect to last weekend’s Napa earthquake and its consequences, the occurrence of the earthquake in that particular location was somewhat unexpected, although in the greater Bay Area, future earthquakes of this size have a fairly high probability over the next 3 years. 

You can always go to our hazard viewer  to get a forecast for your regional area, or to estimate the potential damage to your residence.