Hydrogeophysical Evidence of Groundwater Convection in the Nacimiento Fault

Abstract

Theory exists for unstable convective motion in porous and fractured media, and has been detected in the field as fluid fingers in porous media. Groundwater convective theory is limited though due to a lack of field evidence to understand and quantify 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 haline convection in a hydraulically active fault zone. The hypothesis proposed that measured convective parameters of wavelength and timescales obtained from electrical resistivity and fluid data will correlate to convective groundwater theory in fault zones. Over a 2 year period (2011-2012), a total of 16 ERI lines provided two-dimensional and three-dimensional mapping of the convective fluid signatures in the Nacimiento Fault. Additionally, one line of transient data evaluated changes in the fault over a 6 day timescale. The results show circular conductive features which change over time as well as EC oscillations in transducer data.