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Imaging the Fault Damage Zone of the San Jacinto Fault Near Anza With Ambient Noise Tomography Using a Dense Nodal Array
Author(s) -
Wang Yadong,
Allam Amir,
Lin FanChi
Publication year - 2019
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2019gl084835
Subject(s) - geology , seismology , tomography , fault (geology) , rayleigh wave , shear (geology) , fault plane , seismic tomography , surface wave , geophysics , mantle (geology) , physics , petrology , optics
We apply the double‐beamforming tomography to a monthlong temporary dense seismic array to obtain high‐resolution images of the San Jacinto Fault's damage zone. We obtain Rayleigh waves between 0.3‐ and 0.8‐s periods via vertical‐vertical noise cross correlation, apply double beamforming to obtain phase velocities, and apply a piecewise 1‐D least squares inversion to obtain shear velocities in the top 300 m. We observe a ~200‐m‐wide low‐velocity zone that narrows with depth, which we interpret as the main damage zone in addition to two other ~100‐m‐wide subsidiary zones corresponding to secondary damaged structures, agreeing with the distribution of fault zone trapped waves produced by local earthquakes. The primary damage zone asymmetry indicates that materials on the northeast side of the fault are stiffer at seismogenic depth and suggests that large San Jacinto earthquakes tend to nucleate to the southeast and propagate to the northwest.