Improved Visualization of Satellite Radar InSAR Observed Structural Controls at Producing Geothermal Fields Using Modeled Horizontal Surface Displacements

Abstract

Satellite radar InSAR observed deformation patterns around the Bradys, Nevada, USA producing geothermal system contain linear trends defined by steepened or inflected ground deformation gradients. We interpret these as structural controls on reservoir fluid flow (Oppliger et al., 2004 and 2005). We present results of a new technique to analyze these features using horizontal surface strains modeled from InSAR. Our methods allow quantitative mapping of horizontal strain on selected azimuths and the generation of the principal components from the horizontal strain tensor. Strains are mapped in qualitative units (e.g. parts-per-million) and characterized by their sign as tensional or compressive. We show that linear compressive surface strain patterns map directly above the flow axis of a contracting (i.e., cooling or de-pressurized) aquifer zone, whereas associated surface extension will lie outboard of the contracting zone. In the example case at Bradys, the contracting zone over the interferogram period is coincident with an approximately 14ºC (25ºF) drop in temperature and 14 kg/cm2 (200 psi) drop in pressure (Holt et al., 2004).