QUANTIFYING TEMPORAL STRESS CHANGES USING SHEAR-WAVE ANISOTROPY IN THE SAN JACINTO FAULT ZONE

As a shear wave travels through an anisotropic medium, it is polarized into two waves with different velocities. When the waves are recorded by a seismometer, the angle between the fast and slow waves and the delay time between them can be calculated. This information can then be used to determine both the polarization and the degree of anisotropy in the ray path. Shear-wave splitting measurements of this type have long been used to determine the degree of anisotropy in the shallow crust. This anisotropy can be caused by a number of different factors, including geologic layering, preferred mineral alignment, or microcrack orientation. In this study, we examine whether temporal changes in anisotropy can be used as a proxy for changes in the stress state of the crust. We performed shear-wave splitting analysis on events of magnitude greater than 1.5 in the data-rich San Jacinto Fault Zone, California. With this dataset spanning over a decade, we seek to identify temporal patterns in shear-wave fast direction and delay time that may yield insight into the evolving stress state in an active fault system.