RESULTS OF SHALLOW SEISMIC SURVEYS IN CENOZOIC BASINS OF THE SOUTHERN RIO GRANDE RIFT: IMPLICATIONS FOR HYDROLOGY, GEOTHERMAL RESOURCES, AND NEOTECTONICS

During the past several years, we have conducted seismic surveys designed to image the upper 500 to 1000 m of the subsurface within arid basins of the southern Rio Grande Rift. The purposes for acquiring individual surveys have ranged from groundwater resource definition and contamination mitigation, to geothermal resource definition and investigations of faults that may pose an earthquake hazard. Here we present an overview of results from these surveys. From a technical perspective, all of our seismic surveys have been designed to be analyzed as both refraction and reflection surveys. Unsaturated sediments in the shallow subsurface are notoriously difficult to image with near-vertical reflections. By applying refraction analysis to our data, we are able to develop velocity images of the unsaturated zone. In addition, refraction velocity models help place constraints on lithology at depth. Our results come from the Jornada del Muerto, Tularosa, and Hueco Basins. This work has produced intriguing images of water table variations, including possible perched aquifers, and one instance where two otherwise separate aquifers appear to be locally connected. We have imaged low velocity zones in shallow bedrock that represent geothermal reservoirs. Images of fault geometry in the shallow subsurface are contributing to ongoing assessment of earthquake hazards.