HR: 1340h
AN: S23B-1381    [Abstracts]
TI: Plumbing the depths of Seattle's basins with noise correlation
AU: * Delorey, A A
EM: adelorey@u.washington.edu
AF: Earth and Space Sciences, University of Washington, Earth and Space Sciences University of Washington Johnson Hall 070, Box 351310, Seattle, WA 98195-1310, United States
AU: Vidale, J E
EM: john.vidale@gmail.com
AF: Earth and Space Sciences, University of Washington, Earth and Space Sciences University of Washington Johnson Hall 070, Box 351310, Seattle, WA 98195-1310, United States
AB: Seismic hazard assessments depend heavily on near-surface S-wave velocity models. Local S-wave velocity models have traditionally been constructed from P-wave models using a deterministic relationship between P- wave and S-wave velocity, or by interpolating within widely spaced observations of geologic structure. Direct measurement of local S-wave velocities can be difficult due to a lack of local seismicity and because S-waves are not well excited by active source experiments. Shallow S-wave velocities are determined by near-surface geology, which in the Seattle area is a combination of crystalline rock, glacial till, young alluvium, and artificial fill. Because geology and therefore ground shaking can vary considerably within such an urban area, improving the accuracy and resolution of shallow S-wave models is the key to improving seismic hazard assessments and predictions for ground shaking. Short-period surface-wave noise cross-correlation tomography has the potential to improve S-wave velocity models in urban areas with dense arrays of short period and broadband instruments. We apply this technique to the Seattle area for the purposes of developing a new shallow S-wave model for the region for use in hazard assessment. By using data from the SHIPS array as well as permanent stations from the PNSN, we have inter- station distances as short as a few kilometers. This allows us to extract very short period surface waves, which are sensitive to shallow basin structure. Initial results show that both broadband and short-period stations can yield useable cross-correlations. The mean Rayleigh wave group velocity at a period of 5 seconds is ~2.1 km/s in the basins around Puget Sound, with most velocities falling between 1.6 and 2.6 km/s, in contrast to the 2.8 km/s average velocity measured in central and eastern Washington.
DE: 7205 Continental crust (1219)
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
DE: 8169 Sedimentary basin processes
SC: Seismology [S]
MN: 2007 Fall Meeting