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Spatial Variations of Upper Crustal Anisotropy along the San Jacinto Fault Zone in Southern California: Constraints from Shear Wave Splitting Analysis
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  • Enyuan Jiang,
  • Kelly H Liu,
  • Yuan Gao,
  • Xiaofei Fu,
  • Stephen S. Gao
Enyuan Jiang
Missouri University of Science and Technology
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Kelly H Liu
Missouri University of Science and Technology
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Yuan Gao
Key Laboratory of Earthquake Prediction, Institute of Earthquake Forecasting, China Earthquake Administration
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Xiaofei Fu
Northeast Petroleum University
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Stephen S. Gao
Missouri University of Science and Technology

Corresponding Author:sgao@mst.edu

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To discern spatial and explore possible existence of temporal variations of upper crustal anisotropy in an ~15 km section of the San Jacinto Fault Zone (SJFZ) that is composed of the Buck Ridge and Clark faults in southern California, we conduct a systematic shear wave splitting investigation using local S-wave data recorded by three broadband seismic stations located near the surface expression of the SJFZ. An automatic data selection and splitting measurement procedure is firstly applied, and the resulting splitting measurements are then manually screened to ensure reliability of the results. Strong spatial variations in crustal anisotropy are revealed by 1694 pairs of splitting parameters (fast polarization orientation and splitting delay time), as reflected by the dependence of the resulting splitting parameters on the location and geometry of the raypaths. For raypaths traveling through the fault zones, the fast orientations are dominantly WNW-ESE which is parallel to the faults and may be attributed to fluid-filled fractures in the fault zones. For non-fault-zone crossing raypaths, the fast orientations are dominantly N-S which are consistent with the orientation of the regional maximum compressive stress. A three-dimensional model of upper crustal anisotropy is constructed based on the observations. An apparent increase in the raypath length normalized splitting times is observed after the 03/11/2013 M4.7 earthquake, which is largely attributable to changes in the spatial distribution of earthquakes before and after the M4.7 earthquake rather than reflecting temporal changes of upper crustal anisotropy.
Apr 2021Published in Journal of Geophysical Research: Solid Earth volume 126 issue 4. 10.1029/2020JB020876