FAULT CHARACTERIZATION USING INSAR, GPS, AND DEFORMATION MODELING

Horizontal and vertical surface deformations were monitored during a 62-day controlled aquifer test using a high precision GPS network at Mesquite, NV, the site of a new municipal well located in thick alluvial deposits. Initial analysis of the data revealed an anisotropic aquifer system based on the magnitude of observed radial and tangential deformations. However, new InSAR data seem to indicate that the site may be bounded by an oblique normal fault as the subsidence bowl is both truncated to the northwest and offset from the pumping well to the south. A finite-element numerical model was developed using ABAQUS to evaluate the potential location and hydromechanical properties of the fault on the basis of observed horizontal deformations. Simulation results indicate that for the magnitude and direction of motion at the pumping well and at other GPS stations, which is toward the southeast (away from the inferred fault), that the fault zone (5 m wide) must possess a very high permeability and storage coefficient and cross the study area in a northeast-southwest direction. Results of horizontal and vertical displacements with the imposed high permeability fault zone closely match observed displacements indicating that likelihood of the inferred fault. This analysis shows how monitoring horizontal displacements can provide valuable information about faults, and boundary conditions in general, in evaluating aquifer systems during an aquifer test.