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Convergence rates across the Ventura Basin, California

by Huftile, Gary J.

Abstract (Summary)
Four cross sections are balanced and retrodeformed to 250±50 ka and

975±75 ka to yield crustal shortening amounts and rates for the western

Transverse Ranges of California. The cross sections compare the shortening

that occurs along a transfer zone in which displacement is transferred eastward

from a surface reverse fault (Red Mountain fault) to a blind thrust, to a

combination of both a surface reverse fault (San Cayetano fault) and the blind

thrust, and to a surface reverse fault (Modelo lobe segment of the San

Cayetano fault). Deformation can be separated into three phases: (1) pre-

Vaqueros (pre-late Oligocene-early Miocene) tilting in the hanging-wall block

of the Oak Ridge fault that is coincident with normal faulting farther south at

Big Mountain and to the east in the east Ventura basin, (2) Pliocene reverse

faulting and folding, and (3) Quaternary deformation. Crustal shortening rates

have increased through time. For the four cross sections, crustal shortening

rates were 4±4 mm/y, 5±2 mm/y, 6±5 mm/y, and 14±6 mm/y for the interval

between 250 ka and 975 ka. Since 250±50 ka, crustal shortening rates

increased to 23±12 mm/y, 29±7 mm/y, 27±11 mm/y, and 25±11 mm/y. But

crustal convergence rates determined by Global Positioning System (GPS)

surveys, taken over an interval of 2.7 years, indicate a shortening rate of only

7±2 mm/y across the basin. The discrepancy between a rate of strain over a

short, recent time period of little seismic activity, and a faster rate determined

by the offset of bedrock horizons over several hundred thousand years indicates

that much of the present crustal movement is being stored as elastic strain that

could result in the release of energy in damaging earthquakes.

Bibliographical Information:

Advisor:Yeats, Robert S.

School:Oregon State University

School Location:USA - Oregon

Source Type:Master's Thesis

Keywords:plate tectonics california ventura basin geology structural stratigraphic faults

ISBN:

Date of Publication:05/21/1992

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