Informed land-use decisions require information about California’s geologic and seismic hazards. Most local governments and many state agencies lack expertise or information about such hazards and, therefore, must rely on the California Geological Survey to provide such information. Emergency response officials require geologic hazards information to effectively and efficiently plan for future geologic events and develop response activities to such disasters.
The purpose of the Regional Geologic and Hazards Mapping Program is to identify, in space and time, where significant geologic and seismic hazards exist or are likely to exist so that informed land use and emergency response planning decisions can be made. These decisions will reduce or mitigate the dangers to life, property and public safety resulting from such hazards.
Alquist-Priolo Earthquake Fault Zoning Act
Studies of faults result in estimates of maximum earthquake magnitudes and long-term slip rates that are the basic input for seismic hazard calculations. Consensus values are compiled by CGS in cooperation with USGS. Faults that represent a hazard of surface rupture are included in Alquist-Priolo Earthquake Fault Zones.
Probabilistic Seismic Hazards Assessment
Seismic hazards are calculated considering consensus values for earthquake rates based on earthquake history, fault slip rates, and site soil types. The seismic hazard information is combined considering the potential for earthquakes on all seismic sources, and the level of ground shaking that would be caused by those earthquakes. The result is expressed as the level of ground shaking (expressed as a percentage of gravity) that on average occurs every 500 years. These statewide estimates of seismic hazards can then be used to estimate the potential of future earthquake losses.
Historical Earthquakes (and Earthquake Catalogs)
Studies of historic earthquakes provide basic background for projecting future seismic hazards and losses. 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.
Regional Geologic Mapping
CGS's Regional Geologic Mapping Project maps and compiles the geology of the state at various scales with the objective of developing a statewide geologic map database. Collaboration with the U.S. Geological Survey under STATEMAP and SCAMP augments this project.
Landslides, Caltrans Corridor Mapping
The Caltrans Highway Corridor Mapping project began in 2000, and maps existing landslides and potential slope instabilities along the major interstate highways that slice through California's mountainous areas.
Estimating damage done from future earthquakes.
CGS reviews a number of environmental documents and provides comments relating to geologic hazards and issues that apply directly to assessing the potential impacts of land-use modification. As part of this process, CGS provides site reviews on consulting reports in geology, seismology, and geotechnical engineering for public school and hospital construction.
Mineral Hazards Project
The Mineral Hazards Project provides maps, technical information and advice, and monitors activities about minerals-related environmental and public health issues such as naturally occurring heavy metals, asbestos, mercury and radon. Staff are involved in a CalFed funded project to provide information on natural sources of mercury as well as mercury from historic mercury mining activities in the Cache Creek watershed in the Coast Ranges north of San Francisco. As a follow-up to recommendations of the State Air Resources Board (ARB) Asbestos Task Force, staff prepared a statewide map of potential asbestos host rocks. Staff also completed a pilot project to identify areas more likely to contain naturally occurring asbestos (NOA) in western El Dorado County, that serves as a model for NOA studies in other areas of the state. The Project is entering into an interagency agreement with Caltrans, to provide information on NOA occurrence for use in highway construction and maintenance projects throughout the state. Staff will also develop information on NOA for use in training of Caltrans staff. Staff are working with DHS to develop a statewide map and database on radon occurrence, and have completed studies in Santa Barbara and Ventura counties to identify source rocks and soils associated with radon detected in homes and commercial buildings. Staff also completed studies of radon occurrence in schools in various areas of the state. The Project is also under contract with the U.S. Geological Survey to provide up-dated information on certain precious- and base-metal mines throughout the state for use in mineral resource as well as environmental studies.