ELECTRICAL RESISTIVITY IMAGING OF GROUNDWATER CONVECTION IN THE NACIMIENTO FAULT, NEW MEXICO

Theory exists for unstable convective motion in porous and fractured media, and has been detected in porous media in the field. Groundwater convective theory is limited due to a lack of field evidence to understand the process of free convection in other settings such as faults. The Nacimiento Fault Zone in New Mexico was a suitable location for such a field study. This work provides quantification of thermohaline convection in a hydraulically active fault zone. The hypothesis proposed that measured convective parameters of wavelength and timescales obtained from electrical resistivity imaging (ERI) and fluid data will correlate to convective groundwater theory in fault zones. Over a two year period, 2011-2012, 16 ERI lines provided 2-D and 3-D mapping of the convective fluid signatures of the Nacimiento Fault. Additionally, one line of transient data evaluated changes in the fault on a six day time scale. The results show circular conductive features which change over time as well as strong EC changes in transducer data.