Spatial variations of shear wave anisotropy near the San Jacinto Fault Zone in Southern California

Zefeng Li, Zhigang Peng, Yehuda Ben-Zion, & Frank L. Vernon

Published October 31, 2015, SCEC Contribution #6111

We examine crustal anisotropy at several scales along and across the San Jacinto Fault Zone (SJFZ) by systematically measuring shear wave splitting (SWS) parameters. The analyzed data are recorded by 86 stations during 2012-2014, including five linear dense arrays crossing the SJFZ at different locations, and other standalone stations within 15 km from the main fault trace. Shear phase arrivals and SWS parameters (fast directions and delay times) are obtained with automated methods. The quality is then assessed using multiple criteria, resulting in 23000 high quality measurements. We find clear contrast of fast directions between the SW and NE sides of the SJFZ. Stations on the SW side have fast directions consistent overall with the maximum horizontal compression direction (SHmax), while stations on the NE side show mixed patterns likely reflecting lithological/topographic variations combined with fault zone damage. The fast directions in the Anza gap section with relatively simple fault geometry agree with the inferred SHmax, and the delay times at an array within that section are smaller than those observed at other across-fault arrays. These indications of less pronounced damage zone in the Anza section compared to other segments of the SJFZ are correlated generally with geometrical properties of the surface traces. Significant variations of fast directions on several across-fault arrays, with station spacing on the orders of a few tens of meters, suggest that shallow fault structures and near-surface layers play an important role in controlling the SWS parameters.

Key Words
Shear wave anisotropy, San Jacinto Fault, Southern California

Li, Z., Peng, Z., Ben-Zion, Y., & Vernon, F. L. (2015). Spatial variations of shear wave anisotropy near the San Jacinto Fault Zone in Southern California. Journal of Geophysical Research: Solid Earth, 120(12), 8334–8347. doi: 10.1002/2015JB012483.

Related Projects & Working Groups
A systematic measurement of shear wave anisotropy in southern California