HR: 10:20h
AN: G32A-01    [Abstracts]
TI: Delineating Block Boundaries of the Earth's Crust in the Pacific Northwest from GPS and Seismicity
AU: * Qamar, A I
EM: tony@ess.washington.edu
AF: University of Washington, Earth and Space Sciences PO Box 351310, Seattle, WA 98195 United States
AU: McCaffrey, R
EM: mccafr@rpi.edu
AF: Rensselaer Polytechnic Institute, Earth and Environmental Sciences, Troy, NY 12180-3590 United States
AU: King, R W
EM: rwk@chandler.mit.edu
AF: Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA 02139-4307 United States
AU: Vollick, J J
EM: vollij@rpi.edu
AF: Rensselaer Polytechnic Institute, Earth and Environmental Sciences, Troy, NY 12180-3590 United States
AB: GPS measurements indicate that much of the deformation in the Pacific Northwest occurs from the clockwise rotation of the "Oregon block" about a rotation pole located near the eastern end of the Oregon-Washington boundary. Strain rates of less than 1 nanostrain per year in Oregon (corrected for strain due to subduction along the Pacific coast)establish that the Oregon block is relatively rigid as it rotates at 0.8 degrees per million years. The Oregon block may also include part of southwest Washington but in the rest of Washington the rigid block model breaks down and there appears to be significant strain and north-directed compression in the Puget lowland. The details are likely important to understand the nature of earthquake hazards in the Pacific Northwest. In 2004 we reoccupied 60 GPS sites in northeast Oregon, eastern Washington and northern Idaho in order to better define the interaction of the rotating Oregon block and eastern Washington. We focused on sites first surveyed using high precision GPS in 1998 and reoccupied in 2001. Computed velocities at these sites have uncertainties of order 0.8mm/yr or less and indicate a marked change in velocity across the northwest trending Olympic Wallowa lineament, a major tectonic feature cutting through Washington and northeast Oregon. The recomputed velocities east of the Cascade mountains indicate that northeast Washington and northern Idaho move with the rest of stable North America and the observed strain pattern may also explain the increased earthquake activity in central Washington compared to central Oregon.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 1200 GEODESY AND GRAVITY
DE: 1208 Crustal movements--intraplate (8110)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting