Shallow structure and deformation along the San Andreas fault in Cholame Valley, California, based on high-resolution reflection profiling

Journal Article · Tue Apr 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB04p05003· OSTI ID:5009789

Shedlock, K M; Harding, S T ^[1]; Brocher, T M ^[2]

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1. Geological Survey, Golden, CO (United States)
2. Geological Survey, Menlo Park, CA (United States)

The mapped active traces of the San Andreas fault are separated by a 1-km-wide right-stepping offset in Cholame Valley. The authors collected 18 km of high-resolution seismic reflection data specifically designed to image the San Andreas fault zone in the shallow crust surrounding this offset. The reflection profiles and available well data indicate that west of the mapped active traces of the San Andreas fault the shallow subsurface structure of the crust consists of thin ({le} 400 m thick), offset packages of reflections, laterally coherent on the scale of tens of meters, overlying deformed clastic sedimentary rocks. East of the San Andreas fault, the structure of the shallow crust in southern Cholame Valley is characterized by thick packages of reflections, laterally coherent on the scale of kilometers, overlying the Franciscan complex. All of the strata east of the fault (within Cholame Valley) dip toward the San Andreas fault and the offset, into an approximately 1-km-deep sedimentary basin abutting the south strand of San Andreas fault. The offset in Cholame Valley is characterized by a gentle downwarping of sediments into the offset, the presence of many small faults and discontinuous reflections between the traces of the main fault, localized subsidence abutting the main strike-slip fault, the formation of a basin, near the offset, that is about as deep as the jog is wide, and the southward propagation of the deformation associated with the offset. Strain field modeling based on simple geometries of the San Andreas and associated faults successfully predicts the general features of the observed topography and subsurface structure of southern Cholame Valley, including subsidence and basin formation near the offset, a discontinuous San Andreas fault plane, and at least one fault in southeastern Cholame Valley.

• OSTI ID: 5009789
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B4; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
GEOLOGIC FAULTS
GEOMORPHOLOGY
CONTINENTAL CRUST
DEFORMATION
GEOLOGIC HISTORY
GEOLOGIC STRATA
GEOLOGIC STRUCTURES
GROUND SUBSIDENCE
INCLINED STRATA
MAPPING
REFLECTIVITY
SEDIMENTARY ROCKS
SEISMIC SURVEYS
THICKNESS
TOPOGRAPHY
VALLEYS
WELL LOGGING
DEVELOPED COUNTRIES
DIMENSIONS
EARTH CRUST
FEDERAL REGION IX
GEOLOGIC FRACTURES
GEOLOGY
GEOPHYSICAL SURVEYS
NORTH AMERICA
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
ROCKS
SURFACE PROPERTIES
SURVEYS
USA
580000* - Geosciences