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Brief Report for Calaveras fault zone, Central Calaveras fault section (Class A) No. 54b

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Compiled in cooperation with the California Geological Survey

citation for this record: Bryant, W.A., and Cluett, S.E., compilers, 1999, Fault number 54b, Calaveras fault zone, Central Calaveras fault section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website,, accessed 09/20/2014 01:54 AM.

Synopsis General: 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 [1] 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), but there is insufficient data at this time to substantiate seismogenic segments. 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 [section 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 mm/yr ? 5 mm/yr (Kelson and others, 1998 #5518) for the central part of the Calaveras fault [section 54b]. No slip rates have been reported for the southern part of the Calaveras fault [section 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 [section 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].
Physiographic province(s) PACIFIC BORDER
Length (km) This section is 64 km of a total fault length of 156 km.
Average strike N31°W (for section) versus N31°W (for whole fault)
Sense of movement Dextral
Dip Direction V
Historic earthquake
Most recent prehistoric deformation Latest Quaternary (<15 ka)
Slip-rate category Greater than 5.0 mm/yr
Date and Compiler(s) 1999
William A. Bryant, California Geological Survey
Sereyna E. Cluett, California Geological Survey