THE SOUTHERN SAN ANDREAS FAULT EVALUATION (SOSAFE) PROJECT

Simple ridge-transform steps in the Gulf of California grade into complex steps across the Imperial Valley and Little San Bernardino Mountains, as penetrative deformation of the continental crust transfers right-lateral shear strain inboard. Transform shear makes its way inboard of the Sierra Nevada as blocks large and small detach and raft away from North America. The San Andreas fault system may lock up one day, as slip rates adjust through space and time, but until then one has reason to ponder the hazards posed. Hence, the Southern San Andreas Fault Evaluation (SoSAFE) Project will better define the past 2000 years of earthquake occurrence, as well as slip rates along this hazardous and intensively scrutinized fault system. The information obtained is expected to enhance our ability to forecast the occurrence of future destructive earthquakes along the fault system and to better predict aspects of fault system behavior. On January 8-9, 2007 for the sesquicentennial commemoration of the great 1857 Fort Tejon earthquake on the southern San Andreas fault, the Southern California Earthquake Center (SCEC) held a SoSAFE science workshop. Work conducted by SoSAFE researchers is being funded by the USGS Multi-Hazards Initiative through SCEC. SoSAFE paleoseismologists are now making systematic use of the NSF-funded B4 Project LiDAR data set along the entire southern San Andreas and San Jacinto, throughout the B4 coverage area. The SoSAFE Project will furthermore link with NSF's GeoEarthScope and its funding of geochronological support, using radiocarbon and other new dating facilities and methods. Coordinated studies employ novel dating methods and emphasize cross-validation of methods and field sampling techniques to gain a better understanding of actual uncertainties in geologically estimated slip rates over time spans of up to several tens of thousands of years. For example, papers by Sharp et al. and Fletcher et al. at this meeting use U-series dating to re-examine the age of an offset alluvial fan at Biskra Palms Oasis that had been previously dated by cosmogenic methods. At this location, the geodetic slip rate is nearly twice as high as geologic; both rates are reasonably well constrained. This site therefore provides a testing ground for studying the uncertainties in all methods used, and in addressing possible slip rate variation through time.