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Evidence for distributed clockwise rotation of the crust in the northwestern United States from fault geometries and focal mechanisms
Author(s) -
Brocher Thomas M.,
Wells Ray E.,
Lamb Andrew P.,
Weaver Craig S.
Publication year - 2017
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1002/2016tc004223
Subject(s) - geology , seismology , lineament , clockwise , basin and range topography , basin and range province , fault (geology) , quaternary , strike slip tectonics , induced seismicity , subduction , crust , slip (aerodynamics) , cenozoic , structural basin , tectonics , paleontology , rotation (mathematics) , geometry , physics , thermodynamics , mathematics
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.