Geophysics Field Camp 2010

In the spring semester of 2010, the University of Arizona GEOS/GEN 416 Field Studies in Geophysics class, funded by the USGS, collected data in the Upper Santa Cruz River Basin, located in southeastern Arizona, near the US-Mexico border. In this region, surface water is scarce, so the population is almost entirely dependent on ground water. To understand temporal and spatial variability of ground-water quantity and quality, it is necessary to understand the hydrogeology of the subsurface. Using time-domain electromagnetic measurements (TEM), combined with other geophysical data, it is possible to interpret characteristics of the subsurface that might otherwise go unnoticed using just well logs or where well logs are not available. The goal of this work is to develop an understanding of hydrologically significant spatial variations in litho-stratigraphic units in the basin. Using forward and inverse modeling of electromagnetic fields and comparisons with measured data collected by ground based TEM surveys, it is possible to estimate depth to bedrock and water table. Through the analysis of 9 different TEM loops varying in size from 75 to 500 meters, groundwater in the region was interpreted to range from ~20 meters to ~100 meters. Correlation of groundwater with proximity to the Santa Cruz River differs between Guevavi Basin and Highway 82 Basin. Water table depth decreases with proximity to the Santa Cruz in the Guevavi Basin, but increases with proximity in the Highway 82 Basin. Furthermore, none of the TEM loops positively identified any bedrock material, and in some areas the bedrock is determined to be greater than 850 meters depth.The Geophysics Field Camp Reports are made available by the Laboratory for Advanced Subsurface Imaging (LASI) and the University of Arizona Libraries. Visit the LASI website for more information http://www.lasi.arizona.edu