Investigating disagreements between geologically and geodetically estimated slip rates for the San Bernardino and San Gorgonio Pass sections of the San Andreas fault. This award is supporting work aimed at better understanding the rate of slip along the southern San Andreas fault, in a region where highly discordant rates have been reported over different time intervals. The Holocene or latest Pleistocene slip rate (15 to 25 millimeters/year) of the San Bernardino section of the San Andreas fault is 3 to 5 times greater than rates based on elastic modeling of geodetic data (generally less than or equal to 5 millimeters/year). This is one of the largest known discrepancies between present rates of strain accumulation and the rate of Holocene to latest Pleistocene strain release. Does this discrepancy indicate that this section of the fault is no longer as active as it once was? Or is it a result of non-uniform rates of strain accumulation throughout the earthquake cycle? Geodetic data are sparse from the San Bernardino Mountains, along the northeast side of this section of the fault. Thus, before these questions about the cause of the rate discrepancy can be fully resolved, it is important to know to what extent the apparently low rate of geodetic strain accumulation may be an artifact of limited geodetic data in the region. Such information has important implications for assessing hazard associated with fault movement along this part of the San Andreas Fault System. To address these questions, researchers from California State University, San Bernadino an colleagues from the University of Arizona are collecting new survey-mode Global Positioning System (GPS) data from this region in order to provide a refined estimate of the present rate of elastic strain accumulation along the San Bernardino and San Gorgonio Pass sections of the San Andreas fault. Professor Sally McGill (California State University, San Bernardino) leads a team of undergraduate students and high school teachers (accompanied by some of their students) in an annual, week-long campaign to collect new survey-mode GPS data. During each summer from 2009-2011 the team collects 4 to 5 days of GPS data from 25 sites in the San Bernardino Mountains and vicinity. These data are processed and modeled by Sigrún Hreinsdóttir and Rick Bennett (University of Arizona), along with contemporaneous GPS data from up to 25 nearby stations from the Plate Boundary Observatory (PBO) and Southern California Integrated Geodetic Network (SCIGN) networks. This project supports undergraduate students, high school teachers and high school students at a variety of levels. Each summer, eight undergraduate students and six high school teachers with some of their students participate in the week-long data collection campaign. McGill works with the teachers to develop posters and lesson plans that bring their research experience back into the classroom. Each year, two of the undergraduate students develop research projects using the GPS data and continue working on the project throughout the summer, analyzing the time-series and conducting one-dimensional elastic and elastic-viscoelastic modeling for fault slip rates. They present results at professional meetings and are encouraged toward graduate school in the Earth sciences. Special efforts are made to recruit these students from populations that are under-represented in the geosciences, which is facilitated by the fact that California State University, San Bernardino is a Hispanic-serving institution at which 36 percent of the 52 geology majors are from under-represented groups. The education and outreach component of this proposal is being evaluated by an external consultant, Robert deGroot.
