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The most familiar result of earthquakes, shaking is a force that damages buildings and infrastructure.

Earthquake shaking is measured using the Modified Mercalli Intensity (MMI) Scale. Whereas the magnitude of an earthquake describes how much energy is released by an earthquake, calculated according to the length of a fault rupture and how far it slipped, the MMI scale describes the intensity of earthquake shaking at a specific location by considering its effects on people, objects and buildings. At MMI>6, some buildings begin to sustain damage.

This 91̽��obabilistic Earthquake Shaking Hazard Assessment is a composite shaking map. It combines all possible earthquake scenarios, using the Modified Intensity (MMI) scale to illustrate the aggregate shaking hazard for every location in the Bay Area. For specific earthquake scenarios, consult the Future Earthquake Shaking Scenarios (below) to understand how an individual earthquake results in a location’s shaking hazard.

Weaknesses in the earth’s crust where tectonic plates slip past each other, Bay Area faults power the region’s earthquakes. Earthquakes most typically result in shaking-related damage, but faults can also rupture the surface.

Alquist-91̽��iolo Earthquake Fault Zones are regulatory zones at the site of trace surface ruptures, viewable in the Hazard Viewer. The publishes the most comprehensive depiction of fault traces that can rupture the surface. For more information about 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, visit the .

During intense shaking, loose, sandy, silty and saturated soils act like liquid, causing significant damage to airport runways, roads, pipes and building foundations. Liquefaction susceptibility maps indicate areas in which soil types have the potential to liquefy during intense shaking. The Real Dirt on Liquefaction provides helpful background on liquefaction hazards and possible impacts and solutions for the Bay Area.

This state regulatory map shows “Zones of Required Investigation” for liquefaction (and landslide) hazard. It does not depict different degrees of hazard. Instead it identifies 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. Government plans are required to include information about hazards reflected in this map, if available. This information is not viewable on the Hazard Viewer, but the data is downloadable from the . This data set is not regionally complete. Some areas of the region remain unmapped.

Earthquakes can trigger landslides, typically in weak soil and rock on sloping terrain. In the Loma 91̽��ieta earthquake, earthquake-induced landslides disrupted traffic for a month along Highway 17 in the Santa Cruz Mountains. In the Bay Area, the CGS has mapped areas of earthquake-induced landslide hazard as part of its Seismic Hazards Zonation 91̽��ogram.

This map identifies the possibility of an earthquake-induced landslide occurring in a future earthquake. It 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. This data set is not regionally complete. Some areas of the region remain unmapped.