Hydrological And Geoelectrical Analysis Of Groundwater Flow Near Faults
Ball, Lyndsay 1 ; Ge, Shemin 2 ; Caine, Jonathan Saul 3 ; Revil, André 4 ;Jardani, Abderrahim 5
1 Univ. of Colorado/USGS
2 Univ. of Colorado
3 USGS
4 Colorado School of Mines/Univ. de Savoie
5 Univ. de Rouen
Permeability heterogeneity introduced by faults can substantially impact groundwater flow. However, because faults are often poorly exposed at the surface, the architecture of the fault is frequently unobservable and understanding the hydrologic impact of a specific fault is particularly challenging. To improve our ability to estimate fault-zone permeability structure and to document the impact of a major, inactive fault on groundwater flow, we supplemented traditional hydrogeologic measurements with electrical resistivity and self-potential data at the Elkhorn fault in South Park, Colorado.
Water levels and permeability estimates taken in four wells across the fault indicate that permeability generally decreases from the fractured granitic hanging wall to the sedimentary footwall. Resistivity tomography was used in combination with available geologic maps, borehole geophysical and lithologic data, and water-level/permeability data to determine the fault location and geometry. Self-potential measurements co-located with the resistivity data were used to interpret groundwater-flow patterns in the immediate vicinity of the fault and to create a high-resolution interpretation of the hydraulic-head distribution in transects across the fault. The hydrogeologic measurements and geoelectrical data were used to make interpretations about the presence and permeability structure of fault-zone components at the meter to tens-of-meters scale.