Elastic scattering dominates high-frequency seismic attenuation in Southern California

Abstract

We measured high-frequency (1–10 Hz) spectral amplitudes of more than fifty thousand P and S crustal phases from Southern California earthquakes and separately inverted the two datasets for three-dimensional and frequency-dependent models of total attenuation. The independent estimates of the P and S attenuation factors are nearly equal, decay with wavenumber at approximately the same rate, and are strongly correlated in all three spatial dimensions. Attenuation is lower in batholithic regions, higher in deforming regions, and does not correlate with crustal temperatures. We explain the data by combining an absorption-band model of low-frequency anelastic attenuation with a Sato-Fehler scattering model featuring crustal velocity heterogeneities having an outer scale of 8 km, a fractal dimension of 3.85, and a root-mean-square relative amplitude that varies laterally from 5% to 10%. We conclude that elastic scattering from crustal heterogeneities, not anelastic dissipation, dominates high-frequency attenuation in Southern California. Our results disagree with attenuation models derived from coda-wave analysis.