Joint Inversion of Fault Zone Head Waves and Direct P Arrivals for Crustal Structure of the Bear Valley Section of the San Andreas
LEWIS, M. A. and BEN-ZION, Y., University of Southern California, Los Angeles, CA 90089, firstname.lastname@example.org; and MCGUIRE, J., Woods Hole Oceanographic Institution, Woods Hole , MA, 02543, email@example.com
Major faults that have accumulated significant amounts of slip may juxtapose rock with different elastic properties. When an earthquake occurs on the fault in such an arrangement, fault zone head waves (FZHW) may be recorded at instruments within the slower medium in addition to the usual direct waves. FZHW spend the majority of their propagation paths traveling through the fault zone and are thus sensitive to the fault zone structure. Inversions based on a joint analysis of FZHW and direct P waves can provide a high-resolution image for the velocity structure in the immediate vicinity of the fault zone. This is done here for the Bear Valley region of the San Andreas Fault, utilizing data from a dense temporary array of seismometers. Within the operational period, ~1,200 located events were recorded by the array. Data from additional six stations form the Northern California Seismic Network allow us to fill in some spatial gaps. Our joint direct-P and head-wave travel-time inversion confirms the presence of a strong velocity contrast across this section on the San Andreas and shows how it varies with depth and also along-strike. Understanding the structure of large strike-slip faults can be an important step toward the understanding of dynamic earthquake processes.