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Science Tour - 3D/4D mapping of the San Andreas Fault Zone

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Generalized geologic map of northern California showing the San Andreas Fault System and structural elements associated with regional plate tectonics

Northern California regional geology: This maps shows a target investigation area for surficial geology and geophysical mapping in northern California. The region is known for its history of large and damaging earthquakes. Surficial mapping has helped to define the location of faults and the character of bedrock assemblages. These structural elements are partly understood in the framework of a working plate tectonic model in the northern California region. The San Andreas Fault Zone is interpreted as a transform boundary between the North American Plate and the Pacific Plate. North of a major fault triple junction, the Gorda Plate is actively being subducted under the North American Plate. (Through geologic time, the subducting plate has been providing source materials for the volcanic formation of the Cascade Range.) Sandwiched between the San Andreas Fault Zone and the more stable craton of the North American Plate is a section of earth crust referred to as the "Humboldt Plate" (described by Herd, 1978). The Humboldt Plate is a geologically complex region underlain by ancient oceanic crust and younger overlying sediments that have split into mountain-range sized blocks bounded by faults that have been evolved and migrated over time. The goals of scientific investigations have to unravel the geologic history of the region, particularly over the past 30 million years, to help create a better understanding of how the fault system has evolved over time. Resolving the geometric detail and history of the fault systems and the rocks they interact with are crucial to helping resolve key scientific questions, particularly related to earthquake hazards particularly for faults in the region along the eastern margin of the "Humboldt Block" where millions of people currently live.
Graphic provided by Robert McLaughlin
Herd, R. G., 1978, Intercontinental plate boundary east of Cape Mendocino, northern California: Geology, v. 6, p. 721-725/

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