Earthquakes in the San Francisco Bay Region result from accumulation of energy as the Pacific Plate slides past the North American Plate. The fact that a devastating earthquake occurred in 1906 — the San Francisco earthquake — is common knowledge. Larger earthquakes generally affect larger areas; the 1906 earthquake caused extensive damage in San Francisco, Oakland, San Jose and Santa Rosa. More recently, the 1989 Loma Prieta earthquake caused extensive damage in the Santa Cruz Mountains, as well as in Oakland and San Francisco tens of miles away. But many moderate to great earthquakes (over magnitude 6.0) have affected the Bay Area; 22 such events have occurred in the last 160 years — for an average of one every seven years, and future large earthquakes are a certainty. Learn more.
Jump to information about: Liquefaction | Faults | Landslides
Shaking Hazard Map
Source: USGS 2013
This map shows the composite shaking hazard across the Bay Area based on all earthquake scenarios and likelihood information using the Modified Mercalli Intensity (MMI) scale.
To view additional earthquake hazard information, including interactive maps, select a county by clicking on the map or on one of the links below:
Statewide Earthquake Information (California Geological Survey)
Future Earthquake Shaking Scenarios
Source: USGS, 2013.
Liquefaction happens when loosely packed sandy or silty materials saturated with water are shaken hard enough to lose strength and stiffness. Liquefied soils behave like a liquid and are responsible for tremendous damage in an earthquake, causing pipes to leak, roads and airport runways to buckle, and building foundations to be damaged.
Official California Seismic Hazards Zone Map
Source: California Geological Survey (CGS) Seismic Hazards Zonation Program
These maps are State regulatory maps that show “Zones of Required Investigation” for liquefaction (and landslide) hazard. They do not depict different degrees of hazard, rather they identify zones within which site specific studies will be required for new construction. Sellers of properties within a “Zone of Required Investigation” must disclose that fact to prospective buyers.
Liquefaction Susceptibility Map
Mapping Approach – This map shows areas with water-saturated sandy and silty materials that are susceptible to liquefaction if shaken hard enough. This map is not a substitute for a site-specific investigation by a licensed geologist or geotechnical engineer.
Liquefaction Hazard Maps
Source: USGS Open-File Reports 02-296 and 2008-1270
The map predicts the approximate percentage of each designated area that will liquefy and show surface manifestations of liquefaction such as sand boils and ground cracking.
Faults are weaknesses in the earth’s crust that allow plates to slide past each other. Earthquakes occur when forces underground cause the faults beneath us to rupture and suddenly slip. If the rupture extends to the surface, we see movement on a fault (surface rupture). Because faults are weaknesses in the rock, earthquakes tend to occur over and over on these same faults. Strong earthquakes can occur when the fault rupture does not extend to the surface, and fault-related damage is rare when compared to shaking-related damage. More information from USGS.
Alquist-Priolo Earthquake Fault Zone Maps
Source: California Geological Survey from CD-ROM 2001-04 (2001), Official Map of Alquist-Priolo Earthquake Fault Zones.
The California Geological Survey publishes maps of the active faults in the Bay Area that reach the surface as part of its work to implement the requirements of the Alquist-Priolo Earthquake Fault Zone Act. These maps show not only the most comprehensive depiction of fault traces that can rupture the surface, but also the zones in which cities and counties must require special geologic studies to prevent the building of structures intended for human occupancy and in which the surface rupture hazard must be disclosed in real estate transactions.
Earthquakes can trigger landslides on hillsides that can result in significant property damage, injury and loss of life. The only way to know for certain if you home is on an active landslide is for a geotechnical engineer to perform an assessment.
Source: California Geologic Survey (CGS) Seismic Hazards Zonation Program
This map is derived from State-mandated regulatory maps that show “Zones of Required Investigation” for landslide (and liquefaction) hazard. They do not depict different degrees of hazard, rather they identify zones within which site-specific studies will be required for new construction. These zone maps also are used in real estate transactions – sellers of properties within a “Zone of Required Investigation” must disclose that fact to prospective buyers.