Oak Ridge fault, Ventura fold belt, and the Sisar decollement, Ventura basin, California

Journal Article · Thu Dec 01 00:00:00 EST 1988 · Geology; (USA)

DOI:https://doi.org/10.1130/0091-7613(1988)016<1112:ORFVFB>2.3.CO;2· OSTI ID:7144834

Yeats, R S; Huftile, G J; Grigsby, F B ^[1]

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1. Oregon State Univ. Corvallis (USA)

The rootless Ventura Avenue, San Miguelito, and Rincon anticlines (Ventura fold belt) in Pliocene -Pleistocene turbidites are fault-propagation folds related to south-dipping reverse faults rising from a decollement in Miocene shale. To the east, the Sulfur Mountain anticlinorium overlies and is cut by the Sisar, Big Canyon, and Lion south-dipping thrusts that merge downward into the Sisar decollement in lower Miocene shale. Shortening of the Miocene and younger sequence is {approximately} 3 km greater than that of underlying competent Paleogens strata in the Ventura fold belt and {approximately} 7 km greater farther east at Sulfur Mountain. Cross-section balancing requires that this difference be taken up by the Paleogene sequence at the Oak Ridge fault to the south. Convergence is northeast to north-northeast on the base of earthquake focal mechanisms, borehole breakouts, and piercing-point offest of the South Mountain seaknoll by the Oak Ridge fault. A northeast-trending line connecting the west end of Oak Ridge and the east end of Sisar fault separates an eastern domain where late Quaternary displacement is taken up entirely on the Oak Ridge fault and a western domain where displacement is transferred to the Sisar decollement and its overlying rootless folds. This implies that (1) the Oak Ridge fault near the coast presents as much seismic risk as it does farther east, despite negligible near-surface late Quaternary movement; (2) ground-rupture hazard is high for the Sisar fault set in the upper Ojai Valley; and (3) the decollement itself could produce an earthquake analogous to the 1987 Whittier Narrows event in Low Angeles.

• OSTI ID: 7144834
• Journal Information: Geology; (USA), Vol. 16:12, Issue 12; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
GEOLOGIC DEPOSITS
TECTONICS
DEFORMATION
EARTHQUAKES
FORECASTING
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
HAZARDS
RISK ASSESSMENT
SEDIMENTARY BASINS
SEISMOLOGY
SHALES
FEDERAL REGION IX
GEOLOGIC FRACTURES
NORTH AMERICA
ROCKS
SEDIMENTARY ROCKS
SEISMIC EVENTS
USA
580000* - Geosciences