Shallow crustal heterogeneity in Southern California estimated from earthquake coda waves

Nori Nakata, Hongjian Fang, Malcolm C. White, & Arben Pitarka

Published August 12, 2019, SCEC Contribution #9471, 2019 SCEC Annual Meeting Poster #003

High-frequency scattered waves contain important information to reveal small-scale structure such as heterogeneities of velocities and attenuation, which should be considered and included for high-frequency ground motion modeling. Here, we are imaging the 3D scatterer structure in southern California with high spatial resolution using earthquake wavefields. We propose two methods to image the heterogeneities. One is using high-frequency earthquake coda waves. High-frequency earthquake coda waves have been used for studying small-scale heterogeneities of subsurface structures (Aki 1969; Aki and Chouet, 1975). Nishigami (2000) applied the recursive stochastic inversion to image the 3D distribution of scatterers around the San Andreas fault in the central California using local earthquakes and found that the scatterer distribution is related to the geometry of the fault system (Figure 1). We modify Nishigami's method for multi-scattering theory and apply it to Southern California datasets with about 30,000 earthquakes recorded by 300 stations. The second method is using peak delay time of envelope arrival time at different frequencies. We compute pseudo travel-time tomography of the peak delay time, and the tomograms are the proxy of the scattering coefficients of the area. The tomogram shows strong heterogeneities around major faults.

Key Words
heterogeneity, imaging

Nakata, N., Fang, H., White, M. C., & Pitarka, A. (2019, 08). Shallow crustal heterogeneity in Southern California estimated from earthquake coda waves. Poster Presentation at 2019 SCEC Annual Meeting.

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