Reconciling patterns of interseismic strain accumulation with thermal observations across the Carrizo segment of the San Andreas Fault

Abstract

The Carrizo segment of the San Andreas Fault separates rocks of the Salinian Block southwest of the fault characterized by high heat flow (~ 75–95 mW/m 2) and shallow seismicity (<~ 10 km depth), from rocks of the Franciscan Complex and Great Valley Group northeast of the fault associated with low heat flow (50–60 mW/m 2) and deeper seismicity (<~ 20 km depth). GPS data from this region suggest that the northeast side of the fault accommodates more interseismic strain than the southwest side. We show that by incorporating variations in depth to the brittle ductile transition inferred based on heat flow and seismicity data, we fit the geodetic data well and achieve agreement with geologically accepted long-term average slip rates with a ~ 20 km wide zone with low Young's modulus NE of the fault. This wide compliant zone is consistent with observations suggesting that the presence of large overpressures may be decreasing the elastic moduli in this region.