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.
Maps of recent earthquakes and Shakemaps of the intensity of earthquake shaking are available from CISN (California Integrated Seismic Network), a cooperative project of CGS, USGS, CalEMA, Caltech and UC Berkeley.
Studies of historic earthquakes provide basic background for projecting future seismic hazards and losses. Search for more information on historical earthquakes. A map of historic earthquakes of greater than Magnitude 5.5 and earthquake catalogs. Lists of significant California earthquakes and earthquake anniversaries are available here.
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. Click here to view the new 2010 Fault Activity Map of California.
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, by the 2007 Working Group on California Earthquakes, gives the first statewide estimate of earthquake probabilities for the next 30 years.
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 500 years. These calculations for California are part of a cooperative project between USGS and CGS, and are part of the National Seismic Hazard Maps.
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.
The Seismic Hazard Zonation Program maps existing landslides, and designates landslide zones of required investigation that identify areas where a site-specific hazard study and report with recommended countermeasures must be completed before a work permit is approved to construct buildings.
The California Strong Motion Instrumentation Program (CSMIP) records the strong shaking of the ground and in structures during earthquakes throughout California. The measured ground strong shaking is used immediately after an event to assist in emergency response by agencies like CalEMA. Structural measurements are studied after events to analyze the performance of structures, with the goal of mitigating future earthquake impacts through improved building codes for safer, more earthquake resistant structures.