Present-day strain accumulation and slip rates associated with southern San Andreas and eastern California shear zone faults

We present the first results from a dense network of 36 campaign and 46 continuous GPS stations located in the Eastern Transverse Ranges Province (ETR), a transition zone between the southernmost San Andreas fault (SSAF) and eastern California shear zone (ECSZ). We analyzed the campaign data together with available data from continuous GPS stations for the period 1994-2009. We used the GPS velocity estimates to constrain elastic block models to investigate fault-loading rates representing four hypotheses characterized by different fault-block geometries. Fault-block scenarios include blocks bounded by the east-striking left-lateral Pinto Mountain, Blue Cut, and Chiriaco faults of the ETR; blocks bounded by a right-lateral north-northwest striking structure (the "Landers-Mojave earthquake line") that cuts obliquely across the ETR and mapped Mojave Desert faults; and combinations of these end-member hypotheses. Each model implies significantly different active fault geometries, block rotation rates, and slip rates for ETR and ECSZ structures. All models suggest that SSAF slip rate varies appreciably along strike, generally consistent with rates derived from tectonic geomorphology and paleoseismology, with a maximum of ∼23 mm/yr right-lateral along the southernmost Coachella Valley strand, decreasing systematically to <10 mm/yr right-lateral through the San Gorgonio Pass region. Slip rate estimates for the San Jacinto fault are ∼12 mm/yr for all models tested. All four models fit the data equally well in a statistical sense. Qualitative comparison among models and consideration of geologic slip rates and other independent data reveals strengths and weaknesses of each model.