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Brief Report for San Jacinto fault, San Bernardino Valley section (Class A) No. 125a

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Compiled in cooperation with the California Geological Survey

citation for this record: Treiman, J.A., and Lundberg, M.Matthew, compilers, 1999, Fault number 125a, San Jacinto fault, San Bernardino Valley section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website,, accessed 08/28/2014 05:14 PM.

Synopsis General: This is the most seismically active fault in southern California, with significant earthquakes (>M5.5), including surface rupturing earthquakes in 1968 (M6.6 Borrego Mountain earthquake) and 1987 (M6.6 Superstition Hills and M6.2 Elmore Ranch earthquakes), and numerous smaller shocks within each of its main sections. The fault zone in this compilation is divided from north to south into: San Bernardino section [125a], San Jacinto Valley section [125b], Anza section [125c], Coyote Creek section [125d], Borrego Mountain section [125e], Superstition Hills section [125f], and Superstition Mountain section [125g]. Slip rates in the northern half of the fault system are around 12 mm/yr but are only around 4 mm/yr for faults in the southern half where strands overlap or are sub-parallel.

Sections: This fault has 7 sections. Sections taken from segments defined by Working Group on California Earthquake Probabilities (1995 #4945) and by Petersen and others (1996 #4860); Sanders and Magistrale (1997 #6396) defined 18 segments based on inferred and observed historic ruptures and bends or steps in the continuity of the faults (these "segments" are listed under the seven sections described herein). Wesnousky (1986 #5305) divided the fault zone into nine segments, including the entire Claremont fault in the northern segment, including the Casa Loma fault with the Clark fault, and distinguishing the Hot Springs, Thomas Mountain and Buck Ridge faults as separate segments, in addition to the Coyote Creek, Borrego Mountain, Superstition Hills and Superstition Mountain sections as used by Working Group on California Earthquake Probabilities (1995 #4945).
Physiographic province(s) PACIFIC BORDER
Length (km) This section is 51 km of a total fault length of 244 km.
Average strike (for section) versus N58°W (for whole fault)
Sense of movement
Dip Direction NE; SW
Historic earthquake
Most recent prehistoric deformation Latest Quaternary (<15 ka)
Slip-rate category Greater than 5.0 mm/yr
Date and Compiler(s) 1999
Jerome A. Treiman, California Geological Survey
Matthew Lundberg, California Geological Survey