Mapping the extent of fault creep on the Maacama and Rodgers Creek faults in northern California using PS-InSAR

In this study we map the distribution of fault creep from persistent scatterer InSAR (PSI) and estimate the creep rate along the Rodgers Creek and Maacama faults. Fault creep, slow aseismic slip occurring along a fault, is poorly constrained on northern California faults due to the low density of observations along their extents. The Rodgers Creek and Maacama faults both show evidence of fault creep through offset cultural features, such as offset sidewalks and fences, and at alinement arrays placed in locations where creep has been inferred (McFarland et al., 2009). Using PSI, we can constrain the extent of fault creep which can give insight into seismic hazard in the region. Creep reduces the fault area capable of rupturing in an earthquake so, by mapping the areas where creep is occurring, we can infer where the fault is locked (not creeping) thus, we can find areas where the fault is accumulating strain for a future earthquake. We processed a 39 image ERS dataset using the StaMPS PSI code (Hooper et al., 2004), spanning 1992-2000, along the southern Maacama fault and northern Rodgers Creek fault (track 113, frames 2817 & 2835). We estimate fault creep two ways. First, by using profiles through our PSI data to measure the line-of-sight (LOS) velocity changes occurring at the fault. Second, by using elastic dislocation modeling to estimate the lateral and depth distribution of creep on the Rodgers Creek and Maacama faults. We identify fault creep along the Maacama fault around the cities of Ukiah and Willits with LOS velocity rates between 0.1 - 1.6 mm/yr and 1.8 - 1.9 mm/yr, respectively. If projected into the fault parallel direction, and assuming pure right-lateral strike-slip motion, these rates correspond to creep rates of 0.3 - 4.1 mm/yr in Ukiah, and 4.2 - 4.8 mm/yr in Willits. Additional InSAR data from other satellites (e.g. Envisat, ALOS-1, ALOS-2, Sentinel-1A, and Sentinel-1B) and different ERS tracks will be used to supplement these findings.