INSAR AND GPS APPLICATIONS IN AQUIFER DEFORMATION AND SUBSIDENCE STUDIES

The combined use of synthetic aperture radar interferometry (InSAR) together with GPS provides a powerful new set of space-platform tools for detecting, monitoring, and characterizing aquifer deformation and land subsidence in groundwater basins of Nevada. Based on application development studies funded by NASA, InSAR and GPS can provide high-resolution, spatially detailed maps of aquifer deformation in Nevada. Combined with groundwater pumping data and aquifer characteristics in a GIS database, the results can illuminate new insights into aquifer system behavior such as structural-hydraulic controls, displaced aquifer response, elastic and inelastic storage properties, and aquifer recovery resulting from artificial recharge.

Three case history studies show the potential use of these methodologies. In Las Vegas, SAR interferograms revealed new, previously unrecognized subsidence patterns that were undetected in earlier conventional surveys. InSAR demonstrated that the spatial distribution of subsidence was strongly controlled by existing geologic structures (Quaternary faults) despite little to no evidence of structural-hydraulic effects, and that the aquifer deformation is offset from the principal zones of pumping. In addition, InSAR and continuous GPS delineated areas of the valley exhibiting elastic aquifer recovery (uplift) due to artificial recharge. In the Virgin Valley, groundwater pumping for the City of Mesquite has produced similar structurally controlled subsidence in a narrow zone of faulting within the Tertiary sedimentary basin fill based on InSAR studies, and continuous GPS monitoring of a new well has allowed the detection of initial aquifer response. Our InSAR studies have also detected the largest subsidence bowl in Nevada, generated by groundwater pumping related to mine–dewatering. Although pumping is occurring in a quartzite aquifer, a subsidence bowl more than 60 km long with extensive ground fissuring has formed in sedimentary basin fill of the Humboldt River.