San Jacinto fault, San Bernardino Valley section (Class A) No. 125a
Last Review Date: 1999-03-01
Compiled in cooperation with the California Geological Survey
citation for this record: Treiman, J.A., and Lundberg, M., 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, https://earthquakes.usgs.gov/hazards/qfaults, accessed 04/22/2019 07:00 PM.
This is the most seismically active fault in southern California, with significant earthquakes (larger than 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. 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), and include 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]. 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).
General: San Jacinto fault named by Lawson and others (1908 #4969). Later mapping of major parts of zone by Fraser (1931 #6379), Dibblee (1954 #6376) and Sharp (1967 #6397). Major named faults within the zone include the Claremont, Casa Loma, Clark, Buck Ridge, Coyote Creek, Superstition Mountain, and Superstition Hills faults. See section discussions for more detail.
Section: Section represented herein includes Lytle Creek fault (no. 400), Glen Helen fault (no. 402) and San Bernardino Valley portion of Claremont fault (no. 447) of Jennings (1994 #2878); also includes Rialto-Colton fault (no. 429 in Jennings, 1994 #2878) and Loma Linda fault; San Jacinto fault of Morton (in Fife and others, 1974 #6378) appears to be same as Claremont fault. Map of Morton (in Fife and others, 1974 #6378) implies that Loma Linda fault may be southeast extension of Glen Helen fault. Section includes Lytle Creek, Glen Helen, and San Bernardino segments of Sanders and Magistrale (Sanders and Magistrale, 1997 #6396). This section extends southeastward from just south of the Cucamonga fault to where the Loma Linda and Claremont faults join, north of San Jacinto Valley.
Fault ID: Refers to numbers 400 (Lytle Creek fault), 401 (San Jacinto fault), 402 (Glen Helen fault), 429 (Rialto-Colton fault), 447 (Claremont fault), 457 (Casa Loma fault), 458 (Hot Springs fault), 459 (Clark fault), 471 (Buck Ridge fault), 478 (Coyote Mountain fault), 479 & 480 (Coyote Creek fault), 504 (Superstition Hills fault), 505 (Superstition Mountain fault) and 506 (Wienert fault) of Jennings (1994 #2878); numbers 2 (Glen Helen fault), 3 (San Jacinto fault), 4 (Lytle Creek fault), 5 (Claremont fault), 6 (Casa Loma fault), 7 (Hot Springs fault), and 8 Clark fault) of Ziony and Yerkes (1985 #5931).
|County(s) and State(s)||
RIVERSIDE COUNTY, CALIFORNIA
SAN BERNARDINO COUNTY, CALIFORNIA
|Reliability of location||
Compiled at 1:24,000 scale.
Comments: Fault traces from State of California Alquist-Priolo Earthquake Fault Zone maps.
The San Jacinto fault zone is a major element of the San Andreas fault system in southern California, with historic earthquakes (if not ground rupture) associated with most of its sections. This dextral fault zone branches off from the San Andreas near Cajon pass and extends southeastward through the Peninsular Ranges for 240 km into southwestern Imperial Valley. Sharp (1967 #6397) believes that this is currently the most active strand of the San Andreas system in southern California, but is relatively young, with only about 24 km of total dextral offset. The fault zone may be divided into four principal sections: the Claremont, Clark, Coyote Creek and Superstition sections which are separated by major discontinuities (Sanders and Magistrale, 1997 #6396). The fault zone is further subdivided for seismic-hazard modeling purposes into from 5 to as many as 20 "segments" by various authors. The principal faults within the zone overlap in a right-stepping fashion, with a major overlap (50 km in length) occurring between the Clark and Coyote Creek faults.
|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||Right lateral|
Comments: Lytle Creek--65° SW.; Claremont (San Jacinto)--30–40° NE.
Site 125-4, San Bernardino: three-dimensional trench study documented deflection and offset of a buried Holocene channel; minimum slip rate determined using 14C-dating (Wesnousky and others, 1991 #6403).
Glen Helen fault marked by faceted ridges, scarp, linear and deflected drainages. Claremont fault marked by scarps, linear and deflected drainages, notches, benches and aligned gullies. Rialto-Colton fault has no recognized geomorphic expression and is known principally as a groundwater barrier (Morton in Fife and others, 1974 #6378; Hart, 1977 #6381).
|Age of faulted surficial deposits||Holocene fluvial deposits (Wesnousky and others, 1991 #6403); terrace deposits (cited by Wesnousky, 1986 #5305).|
|Most recent prehistoric deformation||
latest Quaternary (<15 ka)
Comments: Last event post-dates offset channel deposit dated 1931±109 yr BP (Wesnousky and others, 1991 #6403); pre-instrumental historic earthquakes possibly associated with this section include July 22, 1899 (M6.5), July 23, 1923 (M6.3), and April 21, 1918 (M6.8), but surface rupture is not reported from these events (Wesnousky, 1986 #5305).
Comments: from Wesnousky (1986 #5305)
Greater than 5.0 mm/yr
Comments: Reported slip rates include 12±6 mm/yr (Working Group on California Earthquake Probabilities, 1995 #4945) based on extrapolation of Anza data; 17 mm/yr for the past 0.7 m.y. (Morton and others, 1986 #6389); 6–13 mm/yr estimated by Prentice and others (1986 #6391); 10 mm/yr on Glen Helen/Lytle Creek faults (Wesnousky, 1986 #5305); 2.5 mm/yr for Lytle Creek fault only (Mezger and Weldon, 1983 #6386); 1.7–3.3 mm/yr minimum slip rate on one strand of Claremont fault, southwest of San Bernardino (Wesnousky and others, 1991 #6403). Slip rate assigned by Petersen and others (1996 #4860) for probabilistic seismic hazard assessment for the State of California was 12.0 mm/yr (with minimum and maximum assigned slip rates of 6.0 mm/yr and 18.0 mm/yr, respectively).
|Date and Compiler(s)||
Jerome A. Treiman, California Geological Survey
Matthew Lundberg, California Geological Survey
#6376 Dibblee, T.W., Jr., 1954, Geology of the Imperial Valley region, California, in Jahns, R.H., ed., Geology of southern California: California Division of Mines Bulletin 170, p. 21-28.
#6378 Fife, D.L., Rodgers, D.A., Chase, G.W., Chapman, R.H., Sprotte, E.C., and Morton, D.M., 1974, Geologic hazards in southwestern San Bernardino County, California: California Division of Mines and Geology Special Report 113, 40 p., 13 pls., scale 1:48,000 and 1:750,000.
#6379 Fraser, D.M., 1931, Geology of San Jacinto quadrangle south of San Gorgonio Pass, California—: Mining in California, California Department of Natural Resources, Division of Mines, v. 42, no. 4, p. 494-540.
#6381 Hart, E.W., 1977, Rialto-Colton fault: California Division of Mines and Geology, Fault Evaluation Report FER-30, 5 p.
#2878 Jennings, C.W., 1994, Fault activity map of California and adjacent areas, with locations of recent volcanic eruptions: California Division of Mines and Geology Geologic Data Map 6, 92 p., 2 pls., scale 1:750,000.
#4969 Lawson, A.C., chairman, 1908, The California earthquake of April 18, 1906—Report of the State Earthquake Investigation Commission: Washington, D.C., Carnegie Institution of Washington Publication 87.
#6386 Mezger, L.L., and Weldon, R.J., 1983, Tectonic implications of the Quaternary history of lower Lytle Creek, southeast San Gabriel Mountains: Geological Society of America Abstracts with Programs, v. 15, no. 5, p. 418.
#6389 Morton, D.M., Matti, J.C., Miller, F.K., and Repenning, C.A., 1986, Pleistocene conglomerate from the San Timoteo badlands, southern California—Constraints on strike-slip displacements on the San Andreas and San Jacinto faults: Geological Society of America Abstracts with Programs, v. 18, no. 2, p. 161.
#4860 Petersen, M.D., Bryant, W.A., Cramer, C.H., Cao, T., Reichle, M.S., Frankel, A.D., Lienkaemper, J.J., McCrory, P.A., and Schwartz, D.P., 1996, Probabilistic seismic hazard assessment for the State of California: California Department of Conservation, Division of Mines and Geology Open-File Report 96-08 (also U.S. Geological Open-File Report 96-706), 33 p.
#6391 Prentice, C.S., Weldon, R.J., and Sieh, K., 1986, Distribution of slip between the San Andreas and San Jacinto faults near San Bernardino, southern California: Geological Society of America Abstracts with Programs, v. 18, no. 2, p. 172.
#6396 Sanders, C., and Magistrale, H., 1997, Segmentation of the northern San Jacinto fault zone, southern California: Journal of Geophysical Research, v. 102, no. B12, p. 27,453-27,467.
#6397 Sharp, R.V., 1967, San Jacinto fault zone in the Peninsular Ranges of southern California: Geological Society of America Bulletin, v. 78, p. 705–730.
#5305 Wesnousky, S.G., 1986, Earthquakes, Quaternary faults, and seismic hazards in California: Journal of Geophysical Research, v. 91, no. B12, p. 12,587-12,631.
#6403 Wesnousky, S.G., Prentice, C.S., and Sieh, K.E., 1991, An offset Holocene stream channel and the rate of slip along the northern reach of the San Jacinto fault zone, San Bernardino Valley, California: Geological Society of America Bulletin, v. 103, p. 700-709.
#4945 Working Group on California Earthquake Probabilities, 1995, Seismic hazards in southern California—Probable earthquakes, 1994 to 2024: Bulletin of the Seismological Society of America, v. 85, no. 2, p. 379-439.
#5931 Ziony, J.I., and Yerkes, R.F., 1985, Evaluating earthquake and surface faulting potential, in Ziony, J.I., ed., Evaluating earthquake hazards in the Los Angeles region—An earth-science perspective: U.S. Geological Survey Professional Paper 1360, p. 43–91.