Calaveras fault zone, Southern Calaveras section (Class A) No. 54c
Last Review Date: 1999-03-04
Compiled in cooperation with the California Geological Survey
citation for this record: Bryant, W.A., and Cluett, S.E., compilers, 1999, Fault number 54c, Calaveras fault zone, Southern Calaveras section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults, accessed 06/17/2019 07:49 AM.
Historically active major dextral strike-slip fault that is part of the larger San Andreas fault system. The fault zone extends for about 150 km from the San Ramon area southeast to about 30 km south of Hollister. The fault has a complex linkage to the San Andreas fault zone  along the subparallel Paicines fault, herein considered to be the southernmost part of the Calaveras fault zone. In general, the Calaveras fault zone is expressed as numerous strands that form a zone tens of meters to more than 500 m in width (1982 #5521). Locally the Paicines fault is expressed as a zone as much as 2 km wide. Various segmentation models have been proposed by Simpson and others (1992 #5527), Taylor (1992 #5531), Petersen and others (1996 #4860), Working Group on Northern California Earthquake Potential (1996 #1216), and Kelson and others (1998 #5518). In this compilation the fault is divided into 4 sections: from north to south they are the Northern Calaveras [54a], Central Calaveras [54b], Southern Calaveras [54c], and Paicines [54d] sections. There is a distinct change in slip rate and fault behavior north and south of the vicinity of Calaveras Reservoir. North of Calaveras Reservoir, the fault [54a] is characterized by a slip rate of 5–6 mm/yr (Kelson and others, 1996 #5284; Simpson and others, 1999 #5528), sparse seismicity, and it probably ruptures to the surface in moderate to large earthquakes based on interpretation of trench exposures by Kelson and others (1996 #5284) and Simpson and others (1999 #5528). South of Calaveras Reservoir, the fault zone [section 54b] is characterized by historic surface fault creep of as much as 15 mm/yr near the southern end of the central Calaveras fault (Galehouse and Lienkaemper, personal commun. reported in Kelson and others, 1998 #5518). The preferred late Holocene slip rate is 14±5 mm/yr (Kelson and others, 1998 #5518) for the central part of the Calaveras fault [54b]. No slip rates have been reported for the southern part of the Calaveras fault [54c], but historic surface fault creep rates of 4–12 mm/yr have been reported in the Hollister area (Schulz, 1989 #5526; Galehouse, 1999 #5500). The Paicines fault [54d] locally has evidence of historic fault creep at about 5 mm/yr (Harsh and Burford, 1982 #5323), although a partial Holocene dextral slip rate of 9 mm/yr was reported by Perkins and Sims (1988 #5522). An average recurrence interval of between 125 and 850 years was determined for the northern part of the Calaveras fault [54a] (Kelson and others, 1996 #5284; Simpson and others, 1999 #5528). Kelson and others (1998 #5518) reported a preliminary recurrence interval estimate of about 530 yrs for the central part of the Calaveras fault [54b]. No recurrence intervals have been determined for the southern part of the Calaveras fault [54c] and the Paicines [54d] fault. The central part of the Calaveras fault has had two moderate magnitude historical earthquakes (Mw 5.8 1979 Coyote Lake; Mw 6.3 1984 Morgan Hill) associated with minor surface fault rupture (Armstrong, 1979 #5501; Harms and others, 1984 #5511; Hart, 1984 #5517). A moderate magnitude earthquake may have occurred along the northern Calaveras fault in July 1861 according to Rogers and Halliday (1992 #5523) as suggested by a zone of cracking as much as 13 km long. Alternatively, the area where the cracking was reported is characterized by large-scale landsliding and the fractures could be interpreted as secondary shaking or landsliding rather than primary surface fault rupture.
Sections: This fault has 4 sections. There is insufficient data to document seismogenic segments. Petersen and others (1996 #4860) and the Working Group on Northern California Earthquake Potential (1996 #1216) proposed two segments for the Calaveras fault: a northern segment from Calaveras Reservoir north to the San Ramon area, and a southern segment from Calaveras Reservoir to south of Hollister. Taylor (1992 #5531) previously had proposed a similar segmentation model. Simpson and others (1992 #5527), proposed that the Calaveras fault north of the Calaveras Reservoir could be divided into three shorter segments: the Sunol segment, the San Ramon segment, and the Alamo segment. The Working Group on Northern California Earthquake Potential (1996 #1216) also considered these segments as comprising the Northern Calaveras fault. More recently, Kelson and others (1998 #5518) divided the Calaveras fault zone into 3 sections: the Northern Calaveras fault (Danville to Calaveras Reservoir), the Central Calaveras fault (Calaveras Reservoir to San Felipe Lake), and the Southern Calaveras (San Felipe Lake to just south of Hollister). The section boundaries described by Kelson and others (1998 #5518) are adopted for this compilation with the addition of a fourth section south of Hollister that comprises the Paicines fault. The Paicines section extends from the vicinity of the junction of the San Benito River and Tres Pinos Creek south to the vicinity of Stone Canyon. Thus, from north to south the sections are Northern Calaveras [54a], Central Calaveras [54b], Southern Calaveras [54c], and Paicines [54d].
General: The Calaveras fault zone was first mapped, but not named, by Lawson (1908 #4969). Wood (1916 #5259) named the structure the Sunol fault. This name was used until about 1951, when Crittenden (1951 #5509) used the combined name Sunol-Calaveras fault. The simpler name Calaveras fault is preferred herein.
Section: Named by Kelson and others (1998 #5518), the Southern Calaveras fault (section) extends from San Felipe Lake southeast to near the junction of the San Benito River and Tres Pinos Creek and is characterized by fault creep.
Fault ID: Refers to number 227 (Paicines fault) of Jennings (1994 #2878) and numbers C1, C2, C2a, and C2b of Working Group on Northern California Earthquake Potential (1996 #1216).
|County(s) and State(s)||
SANTA CLARA COUNTY, CALIFORNIA
SAN BENITO COUNTY, CALIFORNIA
|Reliability of location||
Compiled at 1:24,000 scale.
Comments: Location based on digital revisions to Jennings (1994 #2878) using original mapping by Bryant (1985 #4803), Dibblee (1979 #4834; 1979 #4835; 1979 #5510), Radbruch-Hall (1974 #1243), and Rogers (1993 #5438) at 1:24,000 scale.
Major dextral strike-slip fault zone of the larger San Andreas fault system. The Calaveras fault zone is located in the eastern San Francisco Bay region and generally trends along the eastern side of the East Bay Hills, bounds the western side of San Ramon Valley, extends into the western Diablo Range, bounds the eastern side of Santa Clara Valley, extends into Hollister Valley, and eventually joins the San Andreas fault zone  along the eastern part of the Gabilan Range. The northern extent of the fault zone is somewhat conjectural. One theory is that the fault zone transfers slip to the Concord fault zone  in a right-releasing step-over (Oppenheimer and MacGregor-Scott, 1992 #5520; Working Group on Northern California Earthquake Probabilities, 1996 #1216). Alternatively, the slip may continue northward along reverse and dextral-reverse faults in the East Bay Hills (Page, 1982 #5521). Page (1982 #5521) estimated that cumulative late Cenozoic dextral offset is about 20±4 km. Sarna-Wojcicki (1992 #5265) reported about 13±7 km of cumulative dextral offset in the past 6 m.y. along the Calaveras —Concord  trend on the basis of offset of the Roblar Tuff.
|Length (km)||This section is 24 km of a total fault length of 156 km.|
|Average strike||N24°W (for section) versus N31°W (for whole fault)|
|Sense of movement||
Comments: The Southern Calaveras section is delineated by geomorphic features indicative of dextral strike-slip faulting. Evidence of historical dextral surface fault creep along the Southern Calaveras fault include measurements from creep-meter stations (Schulz, 1989 #5526), alignment arrays (Galehouse, 1999 #5500), and offset engineered structures (Rogers and Nason, 1971 #5524).
Comments: Many site-specific fault rupture investigations done in compliance with the Alquist-Priolo Earthquake Fault Zoning Act (Hart and Bryant, 1997 #4856) have exposed near vertical faults in unconsolidated alluvium.
Several site-specific fault rupture investigations involving trenching done in compliance with the Alquist-Priolo Earthquake Fault Zoning Act (Hart and Bryant, 1997 #4856) have been performed along traces of the Southern Calaveras section. These sites are not enumerated herein.
The Southern Calaveras section is marked by geomorphic features characteristic of historic and late Holocene dextral strike-slip displacement, such as linear scarps in alluvium, ponded alluvium, closed depressions, linear tonal contrasts on alluvium, pressure ridges, and dextrally offset roads and other structures due to surface fault creep (Rogers and Nason, 1971 #5524; Radbruch-Hall, 1974 #1243; 1979 #5503; 1981 #5506, 1981 #4805; Schulz, 1989 #5526; Rogers, 1993 #5438; Galehouse, 1999 #5500).
|Age of faulted surficial deposits||The Southern Calaveras section is in Hollister Valley, an alluvial-filled basin. Distinctive pressure ridges consisting of deformed Pliocene-Pleistocene San Benito Gravel locally mark the trace of the fault (Rogers, 1993 #5438). Well defined linear scarps along active traces of the Southern Calaveras section have developed on late Holocene alluvium and floodplain deposits. Radiocarbon dates of 2,190±45 yr BP for alluvial unit Qyfm and 3,720±90 yrs BP for alluvial unit Qyff, both offset along the Southern Calaveras section, were reported by Rosenberg (1998 #5525).|
|Most recent prehistoric deformation||
latest Quaternary (<15 ka)
Comments: Timing of the most recent event has not been determined. There is abundant geomorphic evidence of Holocene offset and historic fault creep.
Greater than 5.0 mm/yr
Comments: Slip rates have not been determined for the Southern Calaveras section. Horizontal dispacement rates for the sections north and south of the Southern Calaveras section have been reported by Kelson and others (1998 #5518) for the Central Calaveras section [54b] (preferred 14±5 mm/yr) and by Perkins and Sims (1988 #5522) for the Paicines fault [54d] (9 mm/yr, partial slip rate).
|Date and Compiler(s)||
William A. Bryant, California Geological Survey
Sereyna E. Cluett, California Geological Survey
#5501 Armstrong, C.F., 1979, Coyote Lake earthquake of 6 August 1979: California Geology, v. 32, no. 32, p. 248-251.
#5503 Bryant, W.A., 1979, Calaveras fault, Hollister quadrangle: California Division of Mines and Geology Fault Evaluation Report FER-94, microfiche copy in Division of Mines and Geology Open-File Report 90-11, 19 p., scale 1:24,000.
#5506 Bryant, W.A., 1981, Calaveras fault, San Felipe quadrangle: California Division of Mines and Geology Fault Evaluation Report FER-114, microfiche copy in California Division of Mines and Geology Open-File Report 90-11, scale 1:24,000.
#4803 Bryant, W.A., 1985, Faults in the southern Hollister area, San Benito County, California: California Division of Mines and Geology Fault Evaluation Report FER-113, microfiche copy in California Division of Mines and Geology Open-File Report 90-11.
#5509 Crittenden, M.D., Jr., 1951, Geology of the San Jose-Mt. Hamilton area, California: California Division of Mines Bulletin 157, 1 pl., scale 1:62,500.
#4834 Dibblee, T.W., Jr., 1979, Preliminary geologic map of the Paicines quadrangle, San Benito and Monterey Counties, California: U.S. Geological Survey Open-File Report 79-290, 1 sheet, scale 1:24,000.
#4835 Dibblee, T.W., Jr., 1979, Preliminary geologic map of the Cherry Peak quadrangle, San Benito County, California: U.S. Geological Survey Open-File Report 79-703, 1 sheet, scale 1:24,000.
#5510 Dibblee, T.W., Jr., 1979, Preliminary geologic map of the Tres Pinos quadrangle, San Benito County, California: U.S. Geological Survey Open-File Report 79-702, 1 sheet, scale 1:24,000.
#5500 Galehouse, J.S., 1999, Theodolite measurement of creep rates on San Francisco Bay region faults: U.S. Geological Survey, Summaries of National Earthquake Hazards Reduction Program, v. 40, USGS Contract 99-HQ-GR-0084 (electronic version available on line at http://erp-web.er.usgs.gov).
#5511 Harms, K.K., Clark, M.M., Rymer, M.J., Bonilla, M.G., Harp, E.L., Herd, D.G., Lajoie, K.R., Lienkaemper, J.J., Mathieson, S.A., Perkins, J.A., Wallace, R.E., and Ziony, J.I., 1984, The April 24, 1984 Morgan Hill, California, earthquake: The search for surface faulting, in Bennett, J.H., and Sherburne, R.W., eds., The 1984 Morgan Hill, California earthquake: California Division of Mines and Geology Special Publication 68, p. 149-160.
#5323 Harsh, P.W., and Burford, R.O., 1982, Alignment-array measurements of fault slip in the eastern San Francisco Bay area, California, in Hart, E.W., Hirschfeld, S.E., and Schulz, S.S., eds., Proceedings Conference on Earthquake Hazards in the eastern San Francisco Bay Area: California Division of Mines and Geology Special Publication 62, p. 251-260.
#5517 Hart, E.W., 1984, Evidence for surface faulting associated with the Morgan Hill, earthquake of April 24, 1981, in Bennett, J.H., and Sherburne, R.W., eds., The 1984 Morgan Hill, California earthquake: California Division of Mines and Geology Special Publication 68, p. 161-173.
#4856 Hart, E.W., and Bryant, W.A., 1997, Fault-rupture hazard zones in California: California Division of Mines and Geology Special Report 42, 38 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.
#5518 Kelson, K.I., Baldwin, J.N., and Randolph, C.E., 1998, Late Holocene slip rate and amounts of coseismic rupture along the Central Calaveras fault, San Francisco Bay Area, California: Technical report to U.S. Geological Survey, National Earthquake Hazards Reduction Program Final Technical Report, Reston, Virginia, under Contract 1434-HQ-97-GR-03151, 26 p.
#5284 Kelson, K.I., Simpson, G.D., Lettis, W.R., and Haraden, C.C., 1996, Holocene slip rate and earthquake recurrence of the northern Calaveras fault at Leyden Creek, northern California: Journal of Geophysical Research, v. 101, no. B3, p. 5961-5975.
#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.
#5520 Oppenheimer, D.H., and MacGregor-Scott, N., 1992, The seismotectonics of the Eastern San Francisco Bay region, in Borchardt, G., and others, eds., Proceedings of the Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area: California Department of Conservation, Division of Mines and Geology Special Publication 113, p. 11-16.
#5519 Oppenheimer, D.H., Bakun, W.H., and Lindh, A.G., 1990, Slip partitioning of the Calaveras fault, California, and prospects for future earthquakes: Journal of Geophysical Research, v. 95, no. B6, p. 12,083-12,0958483-8498.
#5521 Page, B.M., 1982, The Calaveras fault zone of California—An active pl. boundary element, in Hart, E.W., Hirschfeld, S.E., and Schulz, S.S., eds., Proceedings of Conference on Earthquake Hazards in the Eastern San Francisco Bay Area: California Department of Conservation, Division of Mines and Geology Special Publication 62, p. 175-184.
#5522 Perkins, J.A., and Sims, J.D., 1988, Late Quaternary slip along the Calaveras fault near Hollister, California: Eos, Transactions of the American Geophysical Union, v. 69, no. 44, p. 1420.