Long-term and seasonal ground deformation in the Santa Clara Valley, California, revealed by multi decadal InSAR time series

The Santa Clara Valley, California, is a shallow basin located between the San Andreas and Hayward-Calaveras fault zones. The Valley is known to experience land subsidence and uplift related to groundwater extraction and recharge. We use Small Baseline (SB) Interferometric Synthetic Aperture Radar (InSAR) time series to precisely map time-dependent ground deformation at the scale of the basin, relying on data sets from 4 satellites (ERS1, ERS2, Envisat, and ALOS1) to cover a twenty-year time period (1992-2012). The ground deformation map produced provides constraints on the lateral distribution of water-bearing units in the valley, information that is critical to effectively manage groundwater resources, and on the areas more likely to experience subsidence related ground deformation or flooding. Multi-year and seasonal time-series reveal different ground deformation patterns. Long-term uplift at few millimeters per year dominates east of the Silver Creek fault (SCF) and likely relates to the poroelastic response of the confined aquifer to recovery of groundwater levels since the 1960s. In contrast seasonal uplift and subsidence in winter and summer, respectively, dominate west of the SCF, near San Jose. We compare the InSAR derived deformation to precipitation and well data to explain this seasonal variability. The differential subsidence across the SCF indicates that the fault partitions the shallow confined aquifer and was likely active since the deposition of these Holocene sediments. Relying on the multiple viewing geometries from the different spacecraft we isolate a narrow band of horizontal deformation in the immediate vicinity of the SCF. This zone of high extensional strain is due to the localized differential subsidence and is likely to experience fissuring.