Remote sensing tectonic and groundwater processes in central California using ALOS-1/2 and Sentinel-1 InSAR

The improved spatiotemporal resolution of surface deformation from recent satellite sensors provides a great opportunity to better constrain and understand both tectonic and non-tectonic processes. In central California the primary plate boundary fault system (San Andreas fault) lies adjacent to the San Joaquin Valley (SJV), a vast structural trough that accounts for about one-sixth of the United Sates' irrigated land and one-fifth of its extracted groundwater. The central San Andreas fault (CSAF) displays a range of fault slip behavior with creeping in its central segment that decreases towards its northwest and southeast ends, where it transitions to being fully locked. Despite much progress, many questions regarding fault and groundwater processes in the region still remain. In this study, we combine satellite InSAR and in-situ GPS to image fault and anthropogenic deformation. We performed a synoptic InSAR time series analysis using Sentinel-1, ALOS-1/2 interferometry. We estimate azimuth mis-registration between single look complex (SLC) images of Sentinel-1 in a stack sense to achieve accurate azimuth co-registration between SLC images for low coherence and/or long interval interferometric pairs. We show that it is important to correct large-scale ionosphere features in ALOS-2 ScanSAR data for accurate deformation measurements. In addition to fault creep, the L-band ALOS, and especially ALOS-2 ScanSAR interferometry, show large-scale ground subsidence in the SJV due to over-exploitation of groundwater. Groundwater related deformation is spatially and temporally variable and is composed of both recoverable elastic and non-recoverable inelastic components. InSAR time series are compared to GPS and well-water hydraulic head in-situ time series to understand water storage processes and mass loading changes. We present model results to assess the influence of hydrological processes on surface deformation, fault mechanics and implication for regional earthquake hazard.