USING GPS TO INVESTIGATE SLIP RATES ALONG FAULTS IN A TRANSECT ACROSS THE PLATE BOUNDARY THROUGH SAN BERNARDINO, CA

The purpose of this study is to enhance our understanding of strain distribution among the faults of the plate boundary system in Southern California. Previous studies have suggested a discrepancy between slip rates measured geologically versus geodetically for the San Bernardino section of the San Andreas fault, with geologic studies yielding somewhat higher slip rates than geodetic studies. To investigate this possible discrepancy, since 2002 we have collected new Global Positioning System (GPS) data from sparsely surveyed areas within the San Bernardino Mountains and vicinity. After acquiring new velocities from 32 benchmarks, we used a one-dimensional elastic half-space method to model these data, along with additional crustal velocities from the Southern California Earthquake Center’s Crustal Motion Model 4 (CMM4) and from continuous GPS stations archived at the Plate Boundary Observatory. We used the maximum depth of seismicity to select locking depths for each fault. Using a spreadsheet macro, we tested over 6.75 million different slip rate combinations for 14 faults within a transect across the plate boundary through the San Bernardino Mountains. Our best fitting model assigns a slip rate of 6 mm/yr for the San Andreas fault and 14 mm/yr for the San Jacinto fault. These results are similar to prior geodetic studies and present a slightly lower San Andreas fault slip rate than what has been measured geologically for the past ~35 ka.