Note: Archived report may contain descriptions that are not current.
San Jacinto fault, San Jacinto Valley section (Class A) No. 125b
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 125b, San Jacinto fault, San Jacinto Valley section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults, accessed 02/19/2019 05:12 AM.
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 San Jacinto Valley portion of Claremont fault (no. 447), Hot Springs fault (no. 458), and Casa Loma fault (no. 457) of Jennings (1994 #2878); also Park Hill fault. Preceding faults correspond to four segments of Sanders and Magistrale (1997 #6396). Claremont fault named by Fraser (1931 #6379), but the name has been applied both to the Holocene fault at the southwest margin of the San Timoteo badlands (Fraser, 1931 #6379; Jennings, 1994 #2878) and to an older sub-parallel fault strand roughly 0.5-1.0 km to the northeast (Department of Water Resources, 1959 #6377; Rogers, 1965 #505; Shuler,1953 #6881). However, current usage of the name is for the Holocene main strand of the fault zone in the San Bernardino-San Jacinto Valley area (Hart, 1977 #6381; Kahle, 1987 #6880; Morton, D.M., personal commun., 1999); Hot Springs fault named and diagrammatically mapped by R.T. Hill (as shown by Arnold, 1918 #6373) and later remapped by Fraser (1931 #6379); Casa Loma fault named by (Department of Water Resources, 1959 #6377); Park Hill fault named by (Department of Water Resources, 1959 #6377); the southeastern part of the Casa Loma fault has also been called the Bautista Creek fault (Department of Water Resources, 1959 #6377). The southern end of the main part of this section is at the concealed juncture where the Casa Loma and Claremont faults join to form the Clark fault (Working Group on California Earthquake Probabilities, 1995 #4945); although the subsidiary Hot Springs fault continues further to the southeast, overlapping the northern Anza section.
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
|Reliability of location||
Compiled at 1:24,000 scale.
Comments: Traces based on 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 59 km of a total fault length of 244 km.|
|Average strike||(for section) versus N58°W (for whole fault)|
|Sense of movement||
Right lateral, Normal
Comments: Claremont fault is principally dextral with perhaps some reverse (Proctor, 1962 #6392); Casa Loma appears to be mainly normal (Department of Water Resources, 1959 #6377), but Rasmussen (1981 #6393) reports evidence of dextral component.
Comments: San Jacinto [Claremont] fault measured in aqueduct tunnel (Department of Water Resources, 1959 #6377); Casa Loma fault dips 35?-53? NE.
Claremont fault marked by faceted ridges, notches, scarps, linear gullies and ponded alluvium. Casa Loma fault marked by sinuous scarps, linear gullies and ponded alluvium. Hot Springs fault marked by scarps. Area between Claremont and Casa Loma faults is a sediment filled graben and area between Casa Loma and Park Hill faults is a pressure ridge.
|Age of faulted surficial deposits||Fault offsets Holocene younger alluvium in San Jacinto Valley (Morton, 1972 #6387, 1978 #6388); Plio-Pleistocene Bautista beds of Fraser (1931 #6379).|
|Most recent prehistoric deformation||
latest Quaternary (<15 ka)
Comments: Historic pre-instrumental events include M6.8 or 6.9 on the Claremont fault (04/21/1918) and M6.4 on the Casa Loma (12/25/1899).
Comments: Estimate for Casa Loma fault (Rasmussen, 1981 #6393).
Greater than 5.0 mm/yr
Comments: Reported slip rates include Working Group on California Earthquake Probabilities (1988 #5494) estimate of 12.0?6.0 mm/yr based on data from the Clark fault, to the south, 8-12 mm/yr (Sharp, 1981 #6398); 13-26 mm/yr, between 43-67 ka and 7-13 mm/yr between 305-700 ka (Kendrick and others, 1994 #6383); Wesnousky (1986 #5305) assigned 10 mm/yr. 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
#6373 Arnold, R., 1918, Topography and fault system of the region of the San Jacinto earthquake: Bulletin of the Seismological Society of America, v. 8, p. 68-73.
#6377 Department of Water Resources, 1959, Appendix B—Geology of San Jacinto and Elsinore units, in Santa Ana river investigation: California Department of Water Resources Bulletin 15, p. 99-126.
#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.
#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.
#6880 Kahle, J.E., 1987, The San Jacinto fault zone (the Claremont, Casa Loma, and related faults) in the Lakeview and El Casco quadrangles, Riverside County, California: California Division of Mines and Geology, unpublished Fault Evaluation Report FER-179, July 21, 1987, 9p.
#6383 Kendrick, K., McFadden, L., and Morton, D., 1994, Soils and slip rates along the northern San Jacinto fault, in McGill, S.F., and Ross, T.M., eds., Geological investigations of an active margin: Geological Society of America, Cordilleran Section, 27th Annual Meeting, San Bernardino, Guidebook, p. 146-151.
#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.
#6387 Morton, D.M., 1972, Geology of the Lakeview and Perris (7 1/2") quadrangles, Riverside County, California: California Division of Mines and Geology Map Sheet 19, scale 1:24,000.
#6388 Morton, D.M., 1978, Geologic map of the Sunnymead quadrangle, Riverside County, California: U.S. Geological Survey Open-File Report 78-22, scale 1:24,000.
#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.
#6392 Proctor, R.J., 1962, Geologic features of a section across the Casa Loma fault, exposed in an aqueduct trench near San Jacinto, California: Geological Society of America Bulletin, v. 73, p. 1293-1296.
#6393 Rasmussen, G.S., 1981, Nature of surface rupture and recurrence interval, Casa Loma fault, in Brown, A.R., and Ruff, R.W., eds., Geology of the San Jacinto Mountains: South Coast Geological Society, Annual field trip, Guidebook 9, p. 48-54.
#505 Rogers, T.H., compiler, 1965, Geologic map of California, Olaf R. Jenkins edition, Santa Ana sheet: California Division of Mines and Geology, 2 sheets, scale 1:250,000.
#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.
#6398 Sharp, R.V., 1981, Variable rates of late Quaternary strike slip on the San Jacinto fault zone, southern California: Journal of Geophysical Research, v. 86, no. B3, p. 1754-1762.
#6881 Shuler, E.H., 1953, Geology of a portion of the San Timoteo Canyon badlands near Beaumont, California: Los Angeles, University of Southern California, unpublished M.S. thesis, 106p.
#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.
#5494 Working Group on California Earthquake Probabilities, 1988, Probabilities of large earthquakes occurring in California on the San Andreas fault: U.S. Geological Survey Open-File Report 88-398, 62 p.
#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.