Evidence for distributed clockwise rotation of the crust in the northwestern United States from fault geometries and focal mechanisms

Tectonics
By: , and 

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Abstract

Paleomagnetic and GPS data indicate that Washington and Oregon have rotated clockwise for the past 16 Myr. Late Cenozoic and Quaternary fault geometries, seismicity lineaments, and focal mechanisms provide evidence that this rotation is accommodated by north directed thrusting and right-lateral strike-slip faulting in Washington, and SW to W directed normal faulting and right-lateral strike-slip faulting to the east. Several curvilinear NW to NNW trending high-angle strike-slip faults and seismicity lineaments in Washington and NW Oregon define a geologic pole (117.7°W, 47.9°N) of rotation relative to North America. Many faults and focal mechanisms throughout northwestern U.S. and southwestern British Columbia have orientations consistent with this geologic pole as do GPS surface velocities corrected for elastic Cascadia subduction zone coupling. Large Quaternary normal faults radial to the geologic pole, which appear to accommodate crustal rotation via crustal extension, are widespread and can be found along the Lewis and Clark zone in Montana, within the Centennial fault system north of the Snake River Plain in Idaho and Montana, to the west of the Wasatch Front in Utah, and within the northern Basin and Range in Oregon and Nevada. Distributed strike-slip faults are most prominent in western Washington and Oregon and may serve to transfer slip between faults throughout the northwestern U.S.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Evidence for distributed clockwise rotation of the crust in the northwestern United States from fault geometries and focal mechanisms
Series title Tectonics
DOI 10.1002/2016TC004223
Volume 36
Issue 5
Year Published 2017
Language English
Publisher American Geophysical Union
Contributing office(s) Earthquake Science Center
Description 32 p.
First page 787
Last page 818
Country United States
State British Columbia, Oregon, Washington
Other Geospatial Vancouver Island