Poster #220, Seismology

Ambient noise attenuation tomography of Love & Rayleigh waves applied to the Ramona reservation linear array across the San Jacinto Fault Zone with amplitude correction for focusing/defocusing

Xin Liu, Gregory C. Beroza, & Yehuda Ben-Zion
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Poster Presentation

2021 SCEC Annual Meeting, Poster #220, SCEC Contribution #11463
We study seismic properties of near-surface fault zone structure from ambient noise data. The amplitude of the seismic wavefield contains information on seismic attenuation, which is sensitive to rock damage associated with concentrated fractures within the fault zone, and possibly fluids. We extract amplitude decay information with uncertainty from the noise interferometry functions of seismic data recorded by a dense linear array of 65 3-C sensors across the San Jacinto Fault Zone at the Ramona reservation north of Anza, California. Because of the strong heterogeneity due to the complex fault structure in the near surface, we apply a frequency-dependent amplitude correction for focusing/de...focusing effects using inverted phase velocity maps by solving the transport equation. Then we estimate the attenuation structure based on the linear station-triplet method (Liu et al. 2015; Allmark et al. 2018) for both Love and Rayleigh waves. The focusing/defocusing correction significantly improves the Rayleigh wave attenuation tomography results by providing a more accurate representation of strong lateral velocity variations, while it only slightly alters the Love wave attenuation results. The attenuation tomography indicates strong attenuation (low Q values) correlated with known San Jacinto Fault surface traces and damage zone structure. The results also suggest radial anisotropy of shear attenuation, which is expressed by the distinct sensitivity of SH and SV modes to different fracture orientations.