EarthWorks Geospatial Catalog

Faults: Offshore of Bolinas, California, 2009

Author(s)
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Description
This line shapefile contains fault lines for the offshore area of Bolinas, California. The map area straddles the right-lateral transform boundary between the North American and Pacific plates and is cut by several active faults that cumulatively form a distributed shear zone, including the San Andreas Fault, the eastern strand of the San Gregorio Fault, the Golden Gate Fault, and the Potato Patch Fault (Bruns and others, 2002; Ryan and others, 2008). These faults are covered by sediment (mostly unit Qms) with no seafloor expression, and are mapped using seismic-reflection data (see field activities S-8-09-NC and L-1-06-SF). The San Andreas Fault is the primary plate-boundary structure and extends northwest through the southern part of the map area before passing onshore at Bolinas Lagoon. This section of the San Andreas Fault has an estimated slip rate of 17 to 24 mm/yr (U.S. Geological Survey, 2010), and the devastating Great 1906 California earthquake (M 7.8) is thought to have nucleated on the San Andreas a few kilometers south of this map area offshore of San Francisco (e.g., Bolt, 1968; Lomax, 2005). The San Andreas Fault forms the boundary between two distinct basement terranes, Upper Jurassic and Lower Cretaceous melange and graywacke sandstone of the Franciscan Complex to the east, and Late Cretaceous granitic and older metamorphic rocks of the Salinian block to the west. Franciscan Complex rocks (unit KJf, undivided) form seafloor outcrops adjacent to the shoreline southeast of Stinson Beach that are commonly continuous with onshore coastal outcrops. Faults were primarily mapped by interpretation of seismic reflection profile data (see field activities S-8-09-NC and L-1-06-SF). The seismic reflection profiles were collected between 2006 and 2009.In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP) to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats and geology within the 3-nautical-mile limit of California's State Waters. CSMP has divided coastal California into 110 map blocks, each to be published individually as United States Geological Survey Open-File Reports (OFRs) or Scientific Investigations Maps (SIMs) at a scale of 1:24,000. Maps display seafloor morphology and character, identify potential marine benthic habitats and illustrate both the seafloor geology and shallow (to about 100 m) subsurface geology. Data layers for bathymetry, bathymetric contours, acoustic backscatter, seafloor character, potential benthic habitat and offshore geology were created for each map block, as well as regional-scale data layers for sediment thickness, depth to transition, transgressive contours, isopachs, predicted distributions of benthic macro-invertebrates and visual observations of benthic habitat from video cruises over the entire state. These data are intended for science researchers, students, policy makers, and the general public. This information is not intended for navigational purposes.The data can be used with geographic information systems (GIS) software to display geologic and oceanographic information. Additionally, this coverage can provide a geologic map for the public and geoscience community to aid in assessments and mitigation of geologic hazards in the coastal region and sufficient geologic information for land-use and land-management decisions both onshore and offshore. This information is not intended for navigational purposes.
Publisher
Geological Survey (U.S.)
Place(s)
California, Marin County (Calif.), and Pacific Ocean
Subject(s)
Coasts, Faults (Geology), Ocean bottom, Geoscientific Information, and Oceans
Year
2006-2009
Held by
Stanford
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Use and reproduction
This item is in the public domain. There are no restrictions on use.
Copyright
This work is in the Public Domain, meaning that it is not subject to copyright.
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