Frequency‐Dependent Attenuation of P and S Waves in Southern California

Yu-Pin Lin, & Thomas H. Jordan

Published July 20, 2018, SCEC Contribution #8002

Accurate 3-D models of crustal attenuation structure are important for simulating seismic wavefields at high frequencies (f > 1 Hz). In this study, we collected P and S waveforms from 160 regional earthquakes (3.3 ≤ M ≤ 5.7) recorded at 218 broadband stations of Southern California Seismic Network and measured spectral amplitudes of P and S waves in the 1-10 Hz band using integrals over wavelet transforms. We accounted for source structure and geometrical spreading by referencing the spectral amplitudes to values computed from 1-D synthetic seismograms. We first inverted the spectral amplitude data for a 1-D, frequency-dependent crustal attenuation model, obtaining a consistent logarithmic derivative α=dlnQ/dlnf=0.4 ±0.05 for both P and S waves, which is on the low side of that found in most previous studies. Consistent with previous work [e.g., Hauksson and Shearer, 2006], the best-fitting model shows QP/QS < 1 throughout the crust, and this relation plus the frequency dependence suggests that the attenuation at high frequencies is dominated by strong scattering effects [Sato et al., 2012]. The inversions accounted for frequency-dependent variations in the source spectrum and site response. The source spectra roll off at an average rate n of about 2 for both wave types. The station residuals reflect the unresolved attenuation and scattering structure near the surface, and they show stronger attenuation in the Los Angeles region and weaker attenuation in the Peninsular Ranges and Mojave block.

Citation
Lin, Y., & Jordan, T. H. (2018). Frequency‐Dependent Attenuation of P and S Waves in Southern California. Journal of Geophysical Research: Solid Earth, 123(7), 5814-5830. doi: 10.1029/2018JB015448.