CGS released two new and two revised Official Alquist-Priolo Earthquake Fault Zone maps, and eight new and two revised Official Seismic Hazard Zone maps.
Areas covered by new and revised AP Earthquake Fault Zone maps are within Los Angeles and Napa counties, and affect the cities of Beverly Hills, Culver City, Los Angeles, Napa, Santa Monica, Vallejo, and West Hollywood.
Areas covered by new and revised Seismic Hazard Zone maps are within Contra Costa, Riverside and San Mateo counties, and affect the cities of Antioch, Belmont, Brentwood, Burlingame, Foster City, Hillsborough, Menlo Park, Murrieta, Oakley, Redwood City, San Carlos, San Mateo, and Temecula.
CGS released a major revision to its Special Publication 42 (SP 42): Earthquake Fault Zones - A Guide for Government Agencies, Property Owners / Developers, and Geoscience Practitioners for Assessing Fault Rupture Hazards in California. SP 42 has been the primary guidance document since 1975 for providing background regarding the Alquist-Priolo Earthquake Fault Zoning Act (AP Act) and the assessment of surface fault rupture hazard. The 2018 edition is the latest update to this document, with a focus on providing more detailed guidance to government agencies, property owners, and geoscientists who are affected by the AP Act. This edition is freely available on the CGS website as a pdf download.
The Preliminary Geologic Map of the Cedarville 30’ × 60’ Quadrangle, Modoc County, California, by Thomas L.T. Grose, Anne E. Egger, and Matt D. O’Neal, is available as a downloadable PDF file with a companion pamphlet.
The Cedarville Quadrangle is the fourth and final map in a series of adjacent geologic maps, including (from south to north): Susanville, Eagle Lake, Alturas, and Cedarville. The Cedarville Quadrangle spans portions of the Basin and Range and Modoc Plateau geomorphic provinces, and is largely underlain by Tertiary age volcanic rocks and associated volcaniclastic sedimentary rocks. Major geologic features of the area include the Devils Garden Plateau, a region of horizontal strata with little structural relief, the Goose Lake Valley graben, the north-south – trending horst of the Warner Range and the Surprise Valley half graben. The Surprise Valley fault between the Warner Range and Surprise Valley is characterized by fresh scarps in modern alluvium associated with Holocene activity.
CGS is pleased to announce the release of a new geologic map, Geology of the Independence Lake and Hobart Mills 7.5’ Quadrangles, Sierra and Nevada Counties, California (Map Sheet 63), by Arthur Gibbs Sylvester and Gary L. Raines. The map is available only as a printed product from CGS Publications. Price is just $30 each.
This new map covers a portion of the northern Sierra Nevada, just north of Donner Lake and the town of Truckee. The map represents the work of the authors with contributions from 32 students and graduate teaching assistants. Cretaceous hornblende-biotite granodiorite, Miocene and Pliocene andesitic lava flows and volcaniclastic deposits are the principal rock types in the map region. Large areas are covered with Pleistocene glacial drift related to at least three stages of glaciation. Two major fault zones strike northwestward through the region. The faults represent the westward incursion of Basin and Range faulting into this part of the northeastern Sierra Nevada.
The California Geological Survey (CGS) is pleased to announce the release of earthquake regulatory zone maps as a web services product that can be incorporated into geographic information systems (GIS). Access to these maps via the internet provides an alternative to downloading individual 7.5-minute quadrangle maps and an automated way to maintain the most up-to-date versions on individual systems. The web-based earthquake hazard zone maps are now available at this URL:
https://spatialservices.conservation.ca.gov/arcgis/rest/services/CGS_Earthquake_Hazard_Zones and include:
- Alquist-Priolo Earthquake Fault Zones
- Alquist-Priolo Earthquake Fault Zone Fault Traces
- Seismic Hazard Zones for Earthquake-triggered Landslides
- Seismic Hazard Zones for Liquefaction
- Seismic Hazard Zones for Overlapping Areas of Landslide and Liquefaction
- Areas not evaluated for Landslide and Liquefaction Hazards.
Attributes included with these data provide links to reports on how the maps were prepared and to the PDF cartographic versions. Metadata pages are available at:
Access to the 7.5-minute quadrangle tile data is still available through the CGS Information Warehouse (http://maps.conservation.ca.gov/cgs/informationwarehouse). These data include GIS Shapefiles and metadata, GeoPDF cartographic maps, as well as associated reports.