Site Response, Basin Amplification and Anelastic and Scattering Attenuation in Washington and Oregon Determined from Seismograms From the Pacific Northwest Seismic Network

Session: Regional Earthquake Centers: Highlights and Challenges
Type: Oral
Date: 4/28/2020
Time: 03:30 PM
Room: 215 + 220
Description: 

Recordings from regional seismic networks provide valuable information on earthquake ground motions that improve seismic hazard assessments and our understanding of earthquake processes. I used seismograms from the Pacific Northwest Seismic Network to quantify site response, sedimentary basin amplification and crustal attenuation. Relative amplifications of 1-3 Hz shear waves at over 100 sites in Washington and Oregon were determined from coda amplitudes at a fixed elapsed time after the origin time for a set of M3-4 earthquakes. The observed site amplifications are correlated with Vs30 values inferred from surficial geology and topography. Sites on deep basins (Seattle, Tacoma, Tualatin) have higher 1 Hz amplification than non-basin sites with the same inferred Vs30. Basin sites do not show significant amplification at 3 Hz, relative to non-basin sites with the same Vs30. Sites on artificial fill and Holocene alluvium display strong amplification at 1 Hz. The time decay of seismic coda was compared with the decay of S-wave amplitudes with propagation time to constrain the anelastic and scattering Q values in the crust. Initial results indicate that most of the S-wave attenuation in the crust at 1-3 Hz is caused by anelasticity rather than scattering. Distance decays of coda-normalized S-wave amplitudes from M3-4 earthquakes are compared for various paths in the region.

Presenting Author: Arthur Frankel

Authors