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 first 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 1,694 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 increase in the raypath length normalized splitting times is observed after the 03/11/2013 M4.7 earthquake, which is probably 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.


Geosciences and Geological and Petroleum Engineering

Research Center/Lab(s)

Center for High Performance Computing Research

Keywords and Phrases

California; crustal anisotropy; San Jacinto Fault; shear wave splitting; stress field

Geographic Coverage

Southern California

International Standard Serial Number (ISSN)

2169-9313; 2169-9356

Document Type

Article - Journal

Document Version

Final Version

File Type





© 2020 American Geophysical Union, All rights reserved.

Publication Date

01 Apr 2021


Article Location