Quaternary Fault and Fold Database of the United States

qfaults web comp As of January 12, 2017, the USGS maintains a limited number of metadata fields that characterize the Quaternary faults and folds of the United States. For the most up-to-date information, please refer to the interactive fault map.

Santa Ynez fault zone, South Branch section (Class A) No. 87c

Last Review Date: 2000-08-01

citation for this record: Treiman, J.A., compiler, 2000, Fault number 87c, Santa Ynez fault zone, South Branch section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults, accessed 05/13/2024 10:35 PM.

Synopsis General: Other than the basic geologic map location from Dibblee (1950 #5977; 1966 #5978) and a few other local studies, very little is known about most of this fault zone. Paleoseismic studies have been done in only two localities--the Alegria Canyon site along the Santa Ynez, South Branch section [87c] and the Rancho San Marcos site near the assigned section boundary between the Santa Ynez, Western section [87b] and Santa Ynez, Eastern sections [87d]. Although the latter study site, demonstrating Holocene displacement, is tentatively placed in the Santa Ynez, Eastern section [87d], the majority of this section (especially in Ventura County) is very poorly studied with respect to recency of activity. The South Branch is a little better known as a result of investigations in the late 1970's and early 1980's for a proposed Liquefied Natural Gas (LNG) facility (Envicom, 1978 #5981; Yerkes and others, 1980 #5993; Rice and others, 1981 #5986) as well as an earlier study cited by Hart (1978 #5983).

Sections: This fault has 4 sections.
Name comments General:

Section: Section name is taken from the Santa Ynez, South Branch. Santa Ynez, South Branch section [87c] extends from the coast about 4 km west of Highway 101 northeast to its intersection with the Santa Ynez Western section [87b].

Fault ID: Refers to numbers 301 (Pacifico fault), 320 (Santa Ynez fault) and 321 (Santa Ynez fault, south branch) of Jennings (1994 #2878) and number 44 (Santa Ynez fault) of Ziony and Yerkes (1985 #5931).
County(s) and State(s) SANTA BARBARA COUNTY, CALIFORNIA
Physiographic province(s) PACIFIC BORDER
Reliability of location Poor
Compiled at 1:750,000 scale.

Comments: Location digitized from 1:750,000 map of Jennings (1994 #2878).

Geologic setting Santa Ynez fault, an east-west structure along the north side of the Santa Ynez and Topatopa Ranges, is largely responsible for the uplift of these ranges (Dibblee, 1982 #5980). The fault has several kilometers of vertical displacement but also a strong, but unknown sinistral component (Dibblee, 1982 #5980); fault (along with Santa Ynez River fault) is modeled to accommodate clockwise rotation of the Transverse Ranges (Hornafius and others, 1986 #5922).

Length (km) This section is 14 km of a total fault length of 148 km.
Average strike N47°E (for section) versus N83°E (for whole fault)
Sense of movement Reverse

Comments: Yerkes and others (1980 #5993).

Dip 60°

Comments: at shoreline (Yerkes and others, 1980 #5993)

Paleoseismology studies Site 87c-1, Alegria Canyon: several trenches excavated in 1970 and partially re-excavated in 1977 exposed faulted stream terrace of inferred Holocene age and late-Pleistocene marine terrace; age control based on terrace elevation and relative soil development (Envicom, 1978 unpublished studies cited by Hart, 1978 #5983; Yerkes and others, 1980 #5993).

Geomorphic expression seafloor scarp (Yerkes and others, 1980 #5993).

Age of faulted surficial deposits Possible Holocene stream terrace and late Pleistocene marine terrace at Alegria Canyon (Yerkes and others, 1980 #5993).
Historic earthquake
Most recent prehistoric deformation late Quaternary (<130 ka)

Comments: Timing of most recent event based on displacement of inferred Holocene stream terrace (Yerkes and others, 1980 #5993).

Recurrence interval 10 k.y.

Comments: Envicom (1978 #5981) report refers to possibility of "numerous episodes of movement since approximately 40,000 to 50,000"; although "numerous" is not clarified. The consultants infer that Holocene movement may have occurred, implying a recurrence of less than 10 k.y.
Slip-rate category Between 0.2 and 1.0 mm/yr

Comments: Slip-rate range of 0.2 to more than 0.6 mm/yr from Clark and others (1984 #2876) is vertical component only from offset fluvial gravels; Yerkes and others (1980 #5993) suggest that the vertical to lateral ratio may be close to 1.7:1.
Date and Compiler(s) 2000
Jerome A. Treiman, California Geological Survey
References #5974 Arnold, R., and Anderson, R., 1907, Geology and oil resources of the Santa Maria oil district, Santa Barbara County, California: US Geological Survey Bulletin 322, 161 p.

#5975 Clark, D.G., Slemmons, D.B., Caskey, S.J., and dePolo, D.M., 1994, Seismotectonic framework of coastal central California, in Alterman, I.B., McMullen, R.B., Cluff, L.S., and Slemmons, D.B., eds., Seismotectonics of the central California Coast Ranges: Geological Society of America Special Paper 292, p. 9-30.

#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.

#5977 Dibblee, T.W., Jr., 1950, Geology of southwestern Santa Barbara County, California: [California] Division of Mines Bulletin 150, 95 p., 17 pls.

#5978 Dibblee, T.W., Jr., 1966, Geology of the central Santa Ynez Mountains, Santa Barbara County, California: California Division of Mines and Geology Bulletin 186, 99 p., 4 pls.

#5979 Dibblee, T.W., Jr., 1978, Analysis of geologic-seismic hazards to Point Conception LNG terminal site: Technical report to County of Santa Barbara, March 1978, 72 p.

#5980 Dibblee, T.W., Jr., 1982, Geology of the Santa Ynez-Topatopa Mountains, southern California, in Fife, D.L., and Minch, J.A., eds., Geology and mineral wealth of the California Transverse Ranges: South Coast Geological Society, Annual Symposium and Guidebook Number 10, p. 40-56.

#5981 Envicom, 1978, Engineering geologic investigation of potentially active faults, Hollister Ranch, Santa Barbara County, California: Consultants report, January 4, 1978, 8 p. plus attachments (on file with Fault Evaluation Report FER-12 at California Division of Mines and Geology, San Francisco office).

#5982 Hall, C.A., Jr., 1978, Origin and development of the Lompoc-Santa Maria pull-apart basin and its relation to the San Simeon-Hosgri strike-slip fault, western California, in Silver, E.A., and Normark, W.R., eds., San Gregorio-Hosgri fault zone, California: California Division of Mines and Geology Special Report 137, p. 25-31.

#5983 Hart, E.W., 1978, Supplement #1 to fault evaluation report FER-12 [Santa Ynez fault, south branch]: California Division of Mines and Geology Fault Evaluation Report FER-12, microfiche copy in California Division of Mines and Geology Open-File Report 90-12, 2 p.

#5922 Hornafius, J.S., Luyendyk, B.P., Terres, R.R., and Kamerling, M.J., 1986, Timing and extent of Neogene tectonic rotation in the western Transverse Ranges, California: Geological Society of America Bulletin, v. 97, p. 1476-1487.

#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.

#5962 Petersen, M.D., and Wesnousky, S.G., 1994, Review, fault slip rates and earthquake histories for active faults in southern California: Bulletin of the Seismological Society of America, v. 84, no. 5, p. 1608-1649.

#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.

#5986 Rice, S.J., Treiman, J.A., Borchardt, G., Jones, A.L., Mualchin, L., Chapman, R.H., and Sherburne, R.W., 1981, Geologic and seismic hazards evaluation of the proposed Little Cojo Bay LNG terminal site, Point Conception, California: California Division of Mines and Geology Open File Report OFR 82-22, 68 p.

#5989 Sylvester, A.G., and Darrow, A.C., 1979, Structure and neotectonics of the western Santa Ynez fault system in southern California: Tectonophysics, v. 52, p. 389-405.

#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.

#5993 Yerkes, R.F., Greene, H.G., Tinsley, J.C., and Lajoie, K.R., 1980, Seismotectonic setting of Santa Barbara Channel area, southern California: U.S. Geological Survey Open-File Report OFR 80-299, 24 p., 2 pls.

#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.