Distribution of fault creep along northern California faults from Sentinel-1

While fault creep, slow aseismic slip of a fault, is known to occur along the Bartlett Springs and Maacama faults in northern California, the spatial-temporal characteristics of the creep remains poorly understood. Observations are challenged due to the dense vegetation and mountainous region. Advanced time-series Interferometric Synthetic Aperture Radar (InSAR) processing techniques, can be used to increase the spatial density of observations. Earlier publications using historic data from the ERS and Envisat showed promising results but lacked the spatial resolution, predominantly due to the irregular sampling of observations and the issue of vegetation. The Sentinel-1 mission provide game changing opportunities. Here we present results of a 130 acquisition dataset from Sentinel-1, spanning 2015 to 2018, to observe fault creep along the Maacama and Bartlett Springs faults. By identifying areas exhibiting fault creep, we can better constrain areas where the fault is locked and therefore where the fault is accumulating strain for a future earthquake. We use the JPL ISCE software to align each to a common 'super master' date, and then produce over 400 interferograms with baselines < 100 m and timespans of less than one year. We then input these interferograms into the SBAS code implemented in the StaMPS/MTI software; this approach is demonstrated to be most effective in rural areas, such as rural northern California. We estimate relative velocity profiles at regular short intervals along the fault trace by making local double difference across the fault. As tropospheric noise cancels out over short distances, we interpret these velocities in terms of shallow creep (a step change across the fault) or locking (a smooth velocity profile), and hence provide a spatial map of the creep distribution. Lastly, we compare our improvements with those from earlier studies.