HR: 0800h
AN: G51B-0833    [Abstracts]
TI: High-resolution imaging of the anticipated 2005 Cascadia ETS slip transient
AU: * Melbourne, T
EM: tim@geology.cwu.edu
AF: Central Washington University, 400 University Way, Ellensburg, WA 98926 United States
AU: Flake, R
EM: rex@geology.cwu.edu
AF: Central Washington University, 400 University Way, Ellensburg, WA 98926 United States
AU: Santillan, M
EM: marcelo@geology.cwu.edu
AF: Central Washington University, 400 University Way, Ellensburg, WA 98926 United States
AU: Miller, M M
EM: meghan@geology.cwu.edu
AF: Central Washington University, 400 University Way, Ellensburg, WA 98926 United States
AU: Szeliga, W
EM: walter@geology.cwu.edu
AF: Geo Scie and CIRES, University of Colorado, Boulder, CO 80309 United States
AU: Bilham, R
EM: bilham@stripe.colorado.edu
AF: Geo Scie and CIRES, University of Colorado, Boulder, CO 80309 United States
AU: Suszek, N
EM: suszek@colorado.edu
AF: Geo Scie and CIRES, University of Colorado, Boulder, CO 80309 United States
AB: Ten slow thrust-slip events along the northern Cascadia megathrust have been identified to date with a 14-month periodicity, and the next event is due in late summer, 2005. In anticipation, a variety of instrumentation has been installed specifically designed to elucidate the detailed relationship between deformation transients and the seismic signature that accompanies them. A particular target is to constrain the role of fault and pore fluids in triggering transient creep. Roughly 30 continuous, geodetically monumented GPS receivers from the Pacific Northwest Geodetic Array (PANGA) are currently joined by ~20 stations from the Plate Boundary Observatory, which together will provide thorough spatial coverage of the surface deformation field from this next event. Supplementing these instruments are two biaxial long-baseline tiltmeters each of 500 m length. One lies within the southern Puget Sound region of Washington State, near a region of active transient deformation, and the other in northern Puget Sound near the US-Canadian border. The tiltmeters are based on the original Michaelson (1922) design and comprised of buried, half-filled 8" diameter PVC tubes and level throughout their lengths to «". The two tiltmeters show remarkable long term stability and ultra-low instrument noise levels of fractions of a nanoradians over several hours. Model tilts computed from slip distributions inverted from GPS offsets measure as high as several microradians, indicating an effective SNR for LBT detection of slow earthquakes in excess of ~1,000. At the corners of the tiltmeter vaults, L4 seismometers are buried at ~3 meters depth and sample at 40 sps, with three instruments per cluster. In conjunction with nearby instruments from the Pacific Northwest Seismic Network (PNSN), these instruments permit correlation of small static tilt signals to seismic tremor. Finally, an absolute gravity meter has been running continuously since early August 2005 at the southern tiltmeter package and will continue until the event is finished. The anticipated 2005 event will be the first captured simultaneously on such a broad suite of instruments, and at the current writing (9/6/2005) increased rates of observed tremor in the northern Puget region suggest the 2005 event may be nearing initiation. Inferences about the ETS process and the 2005 event in particular from these measurements will be presented.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Geodesy [G]
MN: Fall Meeting 2005