Geodetic exploration of the elastic properties across and within the northern San Andreas Fault zone

Abstract

Relying on densely spaced GPS data collected between 1996 and 2007 and on InSAR data spanning the 1992–2001 time period, we explore the effects of lateral rheological heterogeneities across the San Andreas Fault near Point Reyes on the interseismic velocity field. We evaluate heterogeneous elastic dislocation models, including an asymmetric model with contrasting rigidities on either side of the San Andreas Fault and models with a narrow compliant fault zone that lead to high near-fault strain rates. We show that we cannot resolve a compliant zone from interseismic surface displacement measurements unless independent constraints on the locking depth exist. We infer an 18 ± 1 mm yr − 1 slip rate on the San Andreas Fault with a 10 ± 2 km locking depth and a 40% higher rigidity to the SW of the fault. At Bodega Bay, GPS and EDM data suggest a compliant zone on the SAF with a 50-to-60% rigidity decrease, but 25 km further south we find no evidence for a weak fault zone. This suggests substantial variability in fault zone properties along the San Andreas Fault.