Characterization of the San Andreas Fault by Fault-Zone Trapped Waves at Seismic Experiment Site, Parkfield, California: A Review

Yong-Gang Li

Published April 30, 2022, SCEC Contribution #14318

The San Andreas Fault (SAF) at Parkfield, California has been taken as a seismic experimental site since the 1970s. The San Andreas Fault Observatory at Depth (SAFOD) measured a ~200-m-wide damage zone with a seismic velocity reduction of ~25–30% within the mature SAF at ~3 km depth. Observations and 3-D finite-difference simulations of fault-zone trapped waves (FZTWs) recorded in a sequence of seismic experiments conducted at the Parkfield SAF characterized a low-velocity waveguide in the SAF, likely extending from the surface to ~7-km depth with a width taper from ~200 m to ~100 m, within which seismic wave velocities are reduced by 20–40% and Q is 15–50. The FZTW data recorded before and after the 2004 M6 Parkfield earthquake show that the SAF co-seismically weakened with seismic wave velocities reduced by ~2.5% and consequently healed with seismic velocity recovery by ~1.25% within approximate three months after the mainshock. This chapter is a retrospective review of the results from our previous experiments at the Parkfield SAF, California, we expect that it will be valuable for researchers who are carrying out seismic experiments at the active faults to develop the community models of seismic wave velocity, fault structure and earthquake forecasting in the China Seismic Experimental Site (CSES) and global earthquake regions.

Key Words
San Andreas fault, fault-zone trapped (guided) wave, waveguide effect, dispersion, strong motion, earthquake hazard, propagator matrix, finite-difference simulation, rupture zone width and depth, co-seismic damage, post-seismic healing, seismic experimental site, SAFOD, CSES.

Citation
Li, Y. (2022). Characterization of the San Andreas Fault by Fault-Zone Trapped Waves at Seismic Experiment Site, Parkfield, California: A Review. In Li, Y., & (Eds.), China Seismic Experimental Site - Theoretical Framework and Ongoing Practice, (, pp. 203-245) Not Hispanic or Latino, Singapore: Springer Nature & Higher Education Press https://doi.org/10.1007/978-981-16-8607-8_11.

Related Projects & Working Groups
Seismology