Surface geophysics, Edwards and Trinity Aquifers, central Texas

Abstract

Geophysical methods have been an important component of effective hydrogeologic investigations over the Edwards and Trinity Aquifers in central Texas. Various electrical and electromagnetic methods have been used to map stratigraphy and geologic structure and to locate buried karst features. Geophysical methods can also characterize faults and fractures in the Balcones fault zone. Six case studies across three segments (San Antonio, Barton Springs, and Northern segments) of the Edwards Aquifer show that the locations of buried caves and sinkholes, on all three segments, are best defined using a combination of two- and three-dimensional resistivity imaging and natural potential (self-potential) methods. Localization and characterization of the Haby Crossing and Mount Bonnell faults, which are known to be the most significant faults in the Balcones fault zone, are best accomplished by integrating multiple geophysical methods (e.g., electrical resistivity, natural potential, magnetic, ground-penetrating radar, conductivity, and seismic refraction tomography). It is noted, however, that other karstic regions could respond differently to different geophysical methods and require different primary geophysical methods.