Earthquakes and Faults

The California Geological Survey studies earthquakes to help Californians plan and build earthquake resistant communities. We record the strong ground motion from earthquakes, study the distribution of historic earthquakes and evaluate faults that are the source of earthquakes. We combine that information to prepare maps showing the potential for ground shaking, fault rupture, liquefaction and seismically induced landsliding.

Recent Earthquakes

Trinet logo Maps of recent earthquakes and ShakeMaps of the intensity of earthquake shaking are available from California Integrated Seismic Network.

Historical Earthquakes

Historic earthquake damageStudies of historical earthquakes provide basic background for projecting future seismic hazards and losses. Search for more information on historical earthquakes and earthquake catalogs, as well as a list of significant California earthquakes


Fault rupture Faults are planes of weakness in the earth’s crust where one side has moved relative to the other. They are recognized and mapped by sheared and displaced rock units and by the distinctive landforms created by repeated rupture of the earth’s surface. Descriptions of significant active faults are included in the USGS Quaternary fault and fold database. Digital maps of Quaternary faults are available for download from CGS. Faults that represent a hazard of surface rupture are included in Alquist-Priolo Earthquake Fault Zones. Also see Fault Activity Map of California.

Earthquake Probabilities

PSHA map Earthquake probabilities are calculated by projecting earthquake rates based on earthquake history and fault slip rates. The result is expressed as the probability that an earthquake of a specified magnitude will occur on a fault or within an area. The Uniform California Earthquake Rupture Forecast version 3, by the Working Group on California Earthquake Probabilities, includes an update of input data and new methodology since Uniform California Earthquake Rupture Forecast version 2 (2008).

Earthquake Shaking Hazards

PSHA map Earthquake shaking hazards are calculated considering earthquake magnitudes and rates, the decrease in earthquake shaking with distance, and amplification of shaking by soils. The result is expressed as the level of ground shaking (as a percentage of gravity) that on average occurs every 2,500 years. These calculations for California are part of a cooperative project between USGS and CGS, and are part of National Seismic Hazard Maps.

Earthquake Loss Estimation

The effects of potential earthquakes are described by statewide earthquake loss estimation and planning scenarios. An earthquake planning scenario is a description of a hypothetical earthquake, including projected ground shaking, damage, social disruption and economic losses. The long term effects of possible earthquakes also can be estimated and described as annualized losses: the average loss or casualties per year. Earthquake loss estimation and planning scenarios provide useful information in preparing emergency response plans, developing earthquake hazard mitigation strategies, and evaluating the nature and scope of response and recovery efforts prior to the earthquakes.