Active Tectonics Impact on Society (1986) / Chapter Skim
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1. Active Tectonics Along the Western Continental Margin of the Conterminous United States
1. Active Tectonics Along the Western Continental Margin of the Conterminous United States
Pages 20-29
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From page 20... ...
This mobility is measured and documented 20 by employing many approaches, some instrumental and others through geomorphic and geologic mapping, which are described elsewhere in this volume. In this short paper I review briefly the nature of the crustal deformation taking place at present and back into the geologic past for the past half-million years or so along the western continental margin.
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From page 21... ...
The limited areas where strain patterns and styles of deformation have changed significantly are at plate boundaries' and especially at junctures such as near the Mendocino triple junction. Locally within major plates, as along braided fault zones, deformation styles evolve through time but across limited areas.
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From page 22... ...
CROWELL 5oo X P L A N A T I O N Boundary of active tectonic realm Faults and fracture zones Oblique subduction zone Growing spreading center Base of continental slope Shoreline at present Aoo' ~X ~ FIGURE 1.1 Map showing active-tectonic realms along the western margin of the conterminous United States. Boundaries between realms are transitional.
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From page 23... ...
Transverse Ranges One of the most active regions tectonically in western North America lies athwart the northwestern trend of mountain ranges fringing the continent and is appropriately named the Transverse Ranges. To the southeast the Peninsular Ranges parallel the trend of the continental margin, and to the northwest so do the Coast Ranges, Great Valley of California, and the Sierra Nevada.
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From page 24... ...
The San Fernando earthquake of February 9, 1971, was located within the Transverse Ranges on a fault dipping northward beneath the San Gabriel Mountains (Grantz et al., 1971; Oakeshott, 1975a)
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From page 25... ...
Shear stress between the two lithospheric plates is apparently spread across a region running through broad lowlands near the city of Santa Rosa. The belt of displacements includes the San Andreas Fault on the west and extends well to the east into the high Coast Ranges, roughly on line northwestward from the active Calaveras and Concord Faults.
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From page 26... ...
In fact, wrench faulting forming ahead of the arrival of the San Andreas transform system is recognized 120 km north of the triple junction (Kelsey and Cashman, 1983~. Oregon and Washington Coast Ranges From the Mendocino triple junction, coastal mountain ranges extend on northward from within California through Oregon and Washington.
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From page 27... ...
They will also help in characterizing the style and timing of crustal movements on slices within fault zones themselves. Vast proportions of the mobile belt extending inland from the Pacific Coast are not continuously underlain by young datable strata or datable geomorphic surfaces and so do not lend themselves to geomorphic or geologic study aimed at demarcating episodes of active deformation through time.
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From page 28... ...
(1973~. Tectonic evolution of the Transverse Ranges province as related to the San Andreas Fault system, Stanford Univ.
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From page 29... ...
. Geologic cross section of the central Oregon continental margin, Geol.
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