HR: 0800h
AN: T51C-0694    [Abstracts]
TI: Geophysical characterization of the Muckleshoot Basin, northwestern Washington State
AU: * Carley, S
EM: scarley@lssu.edu
AF: Lake Superior State University, Department of Geology and Physics, Sault Ste. Marie, MI 49783, United States
AU: Liberty, L M
EM: lml@cgiss.boisestate.edu
AF: Boise State University, Department of Geosciences 1910 University Dr, Boise, ID 83725-1536, United States
AU: Pratt, T L
EM: tpratt@ocean.washington.edu
AF: U.S. Geological Survey, School of Oceanography Box 357940 University of Washington, Seattle, Wa 98195, United States
AB: We characterize the Muckleshoot Basin and examine its relationship with the Tacoma and White River fault systems to the west and east, respectively. The Muckleshoot Basin, located east of Tacoma, Washington, was initially defined by seismic tomography data as a 20x25 km basin that extends to 7-9 km depth. A new analysis of gravity and vintage industry seismic-reflection data suggests that the Muckleshoot basin extends east to the base of the Cascades and is segmented into two sub-basins that exhibit post-Neogene deformation. A new 25-km high-resolution seismic-reflection transect indicates that the basin extends to within 10 km of Puget Sound. Along this seismic profile, we observe approximately 1 km of Plio-Pleistocene deposits above steeply dipping Tertiary strata. Isostatic gravity and the new seismic data also suggest that an uplift tied to the active Tacoma fault beneath Puget Sound extends east to the Muckleshoot Basin. The saddle that bisects the Muckleshoot Basin is also along strike with the White River fault that crosses the Cascades Range. We tentatively suggest that the Tacoma fault system extends to the White River fault through the Muckleshoot Basin, a total distance that exceeds 100 km. A fault of this length, if substantiated, would pose a significantly higher seismic hazard within the densely populated Puget Lowland area than current models suggest.
DE: 7221 Paleoseismology (8036)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8108 Continental tectonics: compressional
DE: 8123 Dynamics: seismotectonics
SC: Tectonophysics [T]
MN: 2007 Fall Meeting