UPDATE OF THE PACIFIC NORTHWEST GPS VELOCITY FIELD: A KEY TO THE ACTIVE TECTONICS OF CASCADIA

Surface velocities derived from GPS observations have allowed high resolution views of the active deformation and rotation of the Cascadia forearc and backarc as well as elastic strain accumulation. We present an update of the Pacific Northwest GPS velocity field presented earlier by McCaffrey et al. (Geophys. Jour. Int., 2007) and Payne et al. (Geology, 2008). The new velocity field combines new Scripps Orbit and Permanent Array Center (SOPAC) daily solutions for 1994-2009 for the Basin and Range Geodetic (BARGN), Eastern Basin and Range - Yellowstone (EBRY), Pacific Northwest Geodetic Array (PANGA), Plate Boundary Observatory (PBO), and Western Canada Deformation Array (WCDA) networks (http://sopac.ucsd.edu/processing/gamit) with our solutions using data from surveys conducted by Idaho National Laboratory, Massachusetts Institute of Technology, National Geodetic Survey, Geologic Survey of Canada, Rensselaer Polytechnic Institute, US Geological Survey, University of Washington, and others, 1991-2009. The new field reveals that the large-scale clockwise rotation seen in western Washington and Oregon also extends southward into southern Idaho and the Snake River Plain as well as into the northern Basin and Range of Nevada. The axes of rotation generally fall near the Oregon-Washington-Idaho border. We will present interpretations of the active tectonics of the Cascadia margin from northern California to SW British Columbia, based on this new field. Interpretations of the Snake River Plain region are presented by Payne et al. (this meeting).