Constraining fault-zone hydrogeology through integrated hydrological and geoelectrical analysis

Abstract

International audienceThe hydrogeologic influence of the Elkhorn fault in South Park, Colorado, USA, is examined through hydrologic data supplemented by electrical resistivity tomography and self-potential measurements. Water-level data indicate that groundwater flow is impeded by the fault on the spatial scale of tens of meters, but the lack of outcrop prevents interpretation of why the fault creates this hydrologic heterogeneity. By supplementing hydrologic and geologic data with geoelectrical measurements, further hydrogeologic interpretation is possible. Resistivity profiles and self-potential data are consistent with the interpretation of increased fracturing within 70 m of the fault. Further interpretation of the fault zone includes the possibility of a vertical groundwater flow component in a fractured and relatively high permeability damage zone and one or more relatively low permeability fault cores resulting in a conduit-barrier behavior of the fault zone at the meter to tens-of-meters scale. Calculated hydraulic heads from the self-potential data reveal additional complexity in permeability structure, including a steeper hydraulic gradient immediately west of the interpreted fault trace than suggested by the well data alone

Geology and Hydrogeology of Faults on Cape Breton Island, Nova Scotia, Canada: an overview

“…Consideration of faults as hydrogeologic entities is essential to the study of faulted flow systems (Bense et al 2003;Marler and Ge 2003;Apaydin 2010;Ball et al 2010). Four issues were addressed in defining the Structural HU on Cape Breton Island:…”

“…(4) Fluid flow in faults is generally not well understood, as they are typically poorly exposed, with only a limited portion of their three-dimensional, heterogeneous, internal structure observable (Ball et al 2010). This issue is addressed with a brief summary from the literature, supported by the case studies described below.…”

“…Different combinations of hydraulic gradients, intrinsic permeability, anisotropy, and structural position lead to complex three-dimensional flow paths (Apaydin 2010), steep gradients (Mayer et al 2007;Yechieli et al 2007), compartmentalization of flow systems (Ball et al 2010), and varying structure and hydraulic properties over time and space (Evans et al 1997).…”

Geophysical methods in protected environments. Electrical resistivity tomography

“…La resistividad de las rocas del subsuelo está relacionada con diversos parámetros: los minerales contenidos, la porosidad, el fluido que rellena los poros, el grado de saturación de agua de la roca, la salinidad del fluido, la temperatura, etc. Ejemplos de estudios previos en los que se aplicó este método en estudios hidrogeológicos se pueden encontrar en Ball et al (2010), Ratnakumari et al (2012), Galazoulas et al (2015); en casos de vertederos y detección de cavidades en Meads et al (2003), Chamberst et al (2006), Martínez-Pagan et al (2013) y Martínez-Moreno et al (2013; en zonas kársticas en Zhou et al (2002). Además, el casi inexistente impacto que esta técnica produce sobre el terreno hace de ella una opción muy recomendable para investigar el subsuelo de zonas protegidas con fines científicos o medioambientales.…”

Characterization of a fluvial aquifer at a range of depths and scales: the Triassic St Bees Sandstone Formation, Cumbria, UK

“…11b), typical of faults characterized by relatively highly connected open fractures in their damage zones ( Fig. 4b; Ball et al 2010;Bauer et al 2016;Bense et al 2013;Caine et al 1996;Ciotoli et al 2014;Ran et al 2014;Vignaroli et al 2015). This structural style has been considered a typical characteristic of fluvial deposits, since the argillaceous matrix of the fluvial St Bees Sandstone Formation allows brittle failure at lower stresses with respect to better-sorted sandstone deposits of aeolian origin (Knott 1994).…”