Ventura fault (Class A) No. 91
Last Review Date: 2002-02-19
Compiled in cooperation with the California Geological Survey
citation for this record: Perry, S., and Bryant, W.A., compilers, 2002, Fault number 91, Ventura fault, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults, accessed 04/23/2024 11:50 PM.
| Synopsis |
Ventura fault is a north-dipping reverse-oblique slip fault that is expressed at the surface as a monocline with secondary normal faulting (Sarna-Wojcicki and others, 1976 #1316; Smith, 1976 #6030; Smith, 1978 #6031). Prentice and Powell (1991 #6025) reported evidence of steeply north-dipping faults between 4.5 and 9 m below the surface in borings; otherwise trench investigations done in compliance with California's Alquist-Priolo Earthquake Fault Zoning Act (Hart and Bryant, 1997 #4856) have only exposed secondary normal faults related to monoclinal flexure. There is disagreement as to the seismogenic potential of the fault: Yeats (1982 #6032; 1982 #6033) suggests that the fault is a bending moment fault with no potential for large, damaging earthquakes; Sarna-Wojcicki and others (1976 #1316) and Sarna-Wojcicki and Yeats (1982 #6028) concluded that the Ventura and Pitas Point [180] faults do have the potential for producing damaging earthquakes. Clark and others (1984 #2876) reported late Pleistocene to Holocene dip-slip rate of 0.8-2.4 mm/yr, based on south-facing scarp observed by Sarna-Wojcicki and others (1976 #1316) across Harmon alluvial fan. Various studies (e.g., Sarna-Wojcicki and others, 1976 #1316; Yerkes and others, 1987 #6035; Yerkes and Lee, 1987 #6037; Dahlen, 1989 #6020) have presumed that the onshore Ventura fault is an extension of the offshore Pitas Point fault [180], because of their similar strike and inferred end points west of Ventura (Sarna-Wojcicki and others, 1976 #1316). In this compilation, the Ventura fault name is used for the onshore north-dipping reverse-oblique fault. The offshore Pitas Point fault [180] will be considered separately. |
| Name comments |
Fault first suggested by Putnam (1942 #6026), who noted that terraces in the Ventura area were disrupted by several vertical and south-dipping high angle reverse faults. Ogle and Hacker (1969 #6023) show a north-dipping reverse fault along the south margin of the Ventura Avenue anticline. First named Ventura Foothills fault by Quick (1973 #6027) and Nichols (1974 #6022). Sarna-Wojcicki and others (1976 #1316), who provide the most detailed mapping of the fault, named the fault the Ventura fault and associated this onshore fault with the offshore Pitas Point fault [180]. Ziony and others (1985 #5931) refer to this fault zone as the Pitas Point-Ventura fault. The name Pitas Point fault [180] has also been assigned to the Ventura fault. Fault ID: Refers to number 336 (Ventura fault) of Jennings (1994 #2878) and number 55 (Pitas Point-Ventura fault) of Ziony and others (1985 #5931). |
| County(s) and State(s) |
VENTURA COUNTY, CALIFORNIA |
| Physiographic province(s) |
PACIFIC BORDER |
| Reliability of location |
Good Compiled at 1:24,000 scale. Comments: Location of fault from Qt_flt_ver_3-0_Final_WGS84_polyline.shp (Bryant, W.A., written communication to K.Haller, August 15, 2017) attributed to 1:24,000-scale map by Smith (1976 #6030) augmented by 1:750000-scale map by Jennings (1994 #2878).
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| Geologic setting |
The Ventura fault is a north-dipping reverse-oblique slip fault located in the western Transverse Ranges geomorphic province. The fault extends from the mouth of the Ventura River eastward to near the town of Saticoy. Some workers consider that the Ventura fault extends westward offshore and connects with the Pitas Point fault [180] (e.g., Sarna-Wojcicki and others, 1976 #1316; Yerkes and others, 1987 #6035). Total displacement along the Ventura fault is not well documented. Ogle and Hacker (1969 #6023) reported an apparent vertical separation of 245 m of the Pleistocene Las Posas Formation.
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| Length (km) | 13 km. |
| Average strike | N89°W |
| Sense of movement |
Reverse, Left lateral
Comments: Ogle and Hacker (1969 #6023) reported a 245 m vertical separation of the base of the Pleistocene Los Posas Formation based on oil well data, although they associated this displacement with the Pitas Point fault [180]. Sarna-Wojcicki and others (1976 #1316) and Yerkes and others (1987 #6035) reported that fault is primarily reverse with a component of sinistral strike-slip displacement, based on geomorphic expression of the fault and selected focal plane solutions. Yerkes and others (1987 #6035) estimated 3:1 vertical to horizontal displacement components.
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| Dip |
55°-65° N.
Comments: Dip reported by Yerkes and others (1987 #6035).
|
| Paleoseismology studies |
There have been 28 site-specific investigations using trenching in compliance with the Alquist-Priolo Earthquake Fault Zoning Act (Hart and Bryant, 1997 #4856). These studies principally have attempted to locate Holocene active traces of the Ventura fault. Specific paleoseismic investigations have not been attempted.
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| Geomorphic expression |
The 10-km-long fault is delineated by a south-facing scarp on late Pleistocene and Holocene alluvium.
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| Age of faulted surficial deposits | Fault offsets early to mid-Pleistocene San Pedro Formation (Sarna-Wojcicki and others, 1976 #1316), 80-ka marine terrace deposits (Yerkes and others, 1987 #6035). Sarna-Wojcicki and others (1976 #1316) mapped Holocene Harmon Canyon alluvial fan as offset. |
| Historic earthquake | |
| Most recent prehistoric deformation |
latest Quaternary (<15 ka)
Comments: Timing of the most recent paleoevent is poorly constrained. Sarna-Wojcicki and others (1976 #1316) reported that Harmon Canyon alluvial fan is offset by the Ventura fault. Amino acid racemization ages of rodent bones recovered from 4 m depth below the fan surface range from 5,700 yr BP to 6,300 yr BP (Sarna-Wojcicki and others, 1976 #1316). Clark and others (1984 #2876) estimated age range of 5.7 ka to 15 ka for alluvial fan surface, based on data from Sarna-Wojcicki and others (1976 #1316).
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| Recurrence interval | |
| Slip-rate category |
Between 0.2 and 1.0 mm/yr
Comments: 0.4 mm/yr vertical component reported by Yerkes and others (1987 #6035); value is uplift rate in last 80 ka, based on interpretation of deformation in emergent marine terraces. Clark and others (1984 #2876) and Petersen and Wesnousky (1994 #6024) reported a dip-slip rate of 0.8-2.4 mm/yr, based on the maximum scarp height of 12-13.9 m (assuming fault dips 60? to 90?) reported for the fault (Sarna-Wojcicki and others, 1976 #1316) and an assumed age of 5.7-15 ka, the age range of the Harmon alluvial fan. However, Sarna-Wojcicki and others (1976 #1316) reported age of for the surface of the Harmon alluvial fan is 5.7-6.3 ka, based on amino acid racemization of rodent bones found about 4 m below the fan surface. Slip rate assigned by Petersen and others (1996 #4860) for probabilistic seismic hazard assessment for the State of California was 1.0 mm/yr (with minimum and maximum assigned slip rates of 0.5 mm/yr and 1.5 mm/yr, respectively). |
| Date and Compiler(s) |
2002
Sue Perry, Southern California Earthquake Center/U.S. Geological Survey William A. Bryant, California Geological Survey |
| References |
#2876 Clark, M.M., Harms, K.H., Lienkaemper, J.J., Harwood, D.S., Lajoie, K.R., Matti, J.C., Perkins, J.A., Rymer, M.J., Sarna-Wojcicki, A.M., Sharp, R.V., Sims, J.D., Tinsley, J.C., III, and Ziony, J.I., 1984, Preliminary slip rate table and map of late Quaternary faults of California: U.S. Geological Survey Open-File Report 84-106, 12 p., 5 plates, scale 1:1,000,000. #6020 Dahlen, M.Z., Osborne, R.H., and Gorsline, D.S., 1990, Late Quaternary history of the Ventura mainland shelf, California: Marine Geology 94, p. 317–340. #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. #6022 Nichols, D.R., 1974, Surface faulting, in Seismic and safety elements of the resources plan and program: Ventura County Planning Department, section 11, p. 1-35, 1 pl. #6023 Ogle, B.A., and Hacker, R.N., 1969, Cross section coastal area Ventura county, in Geology and oil fields of coastal areas, Ventura and Los Angeles basins, California: Pacific Section American Association of Petroleum Geologists, Society of Exploration Geophysicists, and Society of Economic Paleontologists and Mineralogists, 44th Annual Meeting Field Trip, Guidebook. #6024 Petersen, M.D., and Wesnousky, S.G., 1994, Fault slip rates and earthquake histories for active faults in southern California: Bulletin of the Seismological Society of America, v. 84, no. 5, p. 1,608-1,649. #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. #6025 Prentice, C.D., and Powell, J.R., 1991, Ventura fault, in Blake, T.F., and Larson, R.A., eds., Engineering geology along the Simi-Santa Rosa fault system and adjacent areas, Simi Valley to Camarillo, Ventura County, California: Southern California Section, Association of Engineering Geologists, 1991 Annual Field Trip, August 24, 1991, field trip guidebook, p. 288-295. #6026 Putnam, W.C., 1942, Geomorphology of the Ventura region, California: Geological Society of America Bulletin, v. 53, p. 691-754, 5 pls. #6027 Quick, G.L., 1973, Preliminary microzonation for surface faulting in Ventura, California area, in Moran, D.E., Slosson, J.E., Stone, R.O., and Yelverton, C.A., eds., Geology, seismicity, and environmental impact: Association of Engineering Geologists, Special Publication, p. 257-262. #6028 Sarna-Wojcicki, A.M., and Yerkes, R.F., 1982, Comment on article by R. S. Yeats on "Low-shake faults of the Ventura Basin, California", in Cooper, J.D., ed., Neotectonics in Southern California: Geological Society of America Cordilleran Section, 78th Annual Meeting, Volume and Guidebook, p. 17-20. #1316 Sarna-Wojcicki, A.M., Williams, K.M., and Yerkes, R.F., 1976, Geology of the Ventura fault, Ventura County, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-781, 3 sheets, scale 1:6,000. #6030 Smith, T.C., 1976, Ventura fault: California Division of Mines and Geology Fault Evaluation Report FER-13, microfiche copy in California Division of Mines and Geology Open-File Report 90-12 with supplements dated September 21, 1977; March 23, 1978; and April 18, 1978, 14 p., scale 1:24,000. #6031 Smith, T.C., 1978, Ventura fault: California Division of Mines and Geology Supplement #3 to Fault Evaluation report FER-13, microfiche copy in Division of Mines and Geology Open-File Report 90-12, 12 p. #6032 Yeats, R.S., 1982, Reply [to Sarna-Wojcicki and Yerkes], in Cooper, J.D., ed., Neotectonics in southern California: Geological Society of America Cordilleran Section, 78th Annual Meeting, Volume and Guidebook, p. 21-23. #6033 Yeats, R.S., 1982, Low-shake faults of the Ventura Basin, California, in Cooper, J.D., ed., Neotectonics in southern California: Geological Society of America Cordilleran Section, 78th Annual Meeting, Volume and Guidebook, p. 3-16. #6037 Yerkes, R.F., and Lee, W.H.K., 1987, Late Quaternary deformation in the western Transverse Ranges, in Recent reverse faulting in the Transverse Ranges: U.S. Geological Survey Professional Paper 1339, p. 71–82. #6035 Yerkes, R.F., Sarna-Wojcicki, A.M., and Lajoie, K.R., 1987, Geology and Quaternary deformation of the Ventura area, in Recent Reverse Faulting in the Transverse Ranges: U.S. Geological Survey Professional Paper 1339, p. 169-178. #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. |