UC Riverside

We revisit the question of whether the Rodgers Creek fault in northern California is creeping, a question with implications for seismic hazard. Using imagery acquired by Envisat between 2003 and 2010, we process two persistent scatterer interferometric synthetic aperture radar (InSAR) data sets, one from an ascending track and the other from a descending track, covering the northernmost segment of the Rodgers Creek fault between the cities of Santa Rosa and Healdsburg. The two different viewing geometries provided by the two different tracks allow us to distinguish vertical velocities, which may reflect nontectonic deformation processes, from fault-parallel velocities, which can be used to identify creep. By measuring offsets in InSAR line-of-sight velocity from 12 fault-perpendicular profiles through both data sets, we identify seven locations where we have a high degree of confidence that creep is occurring (estimated creep rate is more than two standard deviations above zero). The preferred creep rates at these locations are in the range 1.9–6.7 mm/yr, consistent within uncertainty with alignment array measurements. Creep is probable (P≥0.70) at another three locations, defining a creeping zone ∼20 km long in total, extending northwest from Santa Rosa. We also estimate the map patterns of fault-parallel and vertical velocities in the region covered by both data sets; these suggest that the Rodgers Creek fault immediately southeast of Santa Rosa remains locked.