Sonoma County is bounded on the west and the east by earthquake faults. Four active or potentially active earthquake faults are identified within the County’s boundaries by the Alquist-Priolo Earthquake Fault Maps and represent the earthquake scenarios of greatest risk to Sonoma County. The Northern Segment of the San Andreas Fault lies off the west coast of the County, and crosses land at Bodega Bay, goes out to sea and crosses the County again from Fort Ross, past the community of Sea Ranch, exiting the County at its northern border. The Northern Hayward/Rodgers Creek Fault enters Sonoma County at San Pablo Bay and extends northward through the City of Santa Rosa. The Maacama Fault lies to the east of the Healdsburg Fault and continues northward, passing east of the City of Cloverdale. The Hayward/Rogers Creek fault system has the highest likelihood of an M 6.7 or greater earthquake occurring before 2036.
Other potential unknown faults that are at risk of affecting Sonoma County may exist but have not been identified or mapped. Although the epicenter of the magnitude 7.8 1906 San Francisco earthquake was not within Sonoma County’s boundaries, horizontal displacement along the San Andreas Fault averaged 15 feet in Sonoma County and caused major damage in Santa Rosa, Sebastopol, Healdsburg, Petaluma and other communities.
The last major earthquakes in Sonoma County occurred on October 1, 1969. Two earthquakes of Magnitudes 5.6 and 5.7 originated near the juncture of the Rodgers Creek and Healdsburg Faults, approximately two miles north of Santa Rosa. The potential for liquefaction in Sonoma County exists primarily in the wetlands areas adjacent to San Pablo Bay; along the Russian and Petaluma Rivers and Santa Rosa and Sonoma Creeks; the Laguna de Santa Rosa and Santa Rosa Plains.
Sonoma County Hazard Map
Locate the area where you live and click to determine the most damaging earthquake scenario for your area.
Source: USGS, 2013.