Spatial Variations of Upper Crustal Anisotropy Along the San Jacinto Fault Zone in Southern California: Constraints From Shear Wave Splitting Analysis

Abstract

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.

Mantle Flow in the Vicinity of the Eastern Edge of the Pacific‐Yakutat Slab: Constraints From Shear Wave Splitting Analyses

“…The splitting parameters were measured and ranked following the procedures described in Liu and Gao (2013) for XKS and Jiang et al (2021) for local S waves, and are briefly summarized below. For XKS splitting, the procedures were developed based on the minimization of transverse energy technique (Silver & Chan, 1991).…”

Seismic anisotropy in the upper crust around the north segment of Xiaojiang faults in the SE margin of Tibetan Plateau

“…Seismic anisotropy in the crust is ubiquitous [Crampin, 1978;Crampin et al, 1984Crampin et al, , 2003Crampin et al, , 2008Gao et al, 1998Gao et al, , 2011Savage, 1998;Gao and Crampin, 2006;Kaviris et al, 2015Kaviris et al, , 2018Crampin and Gao, 2018;Cao et al, 2019;Jiang et al, 2021]. The characteristics of the crustal deformation, deep tectonic structure, and evolution mechanism of the geodynamics can be learned from the anisotropic information [Silver and Flesch, 2007;Kong et al, 2016;Yang et al, 2017;Huang et al, 2018;Zhang et al, 2018;Zheng et al, 2018;Jiang et al, 2021]. Shear-wave splitting (SWS) measurement is one of the effective ways to obtain the anisotropic parameters.…”