“…Many, if not most, geophysical methods have been previously investigated to varying degrees in the context of fractured rock. These include seismic, ground-penetrating radar, electrical resistivity, induced polarization, self potential, and electromagnetic methods [e.g., Day-Lewis, 2003;Dorn et al, 2011Dorn et al, , 2012Donadille and Al-Ofi, 2012;Herwanger et al, 2004a;Krautblatter et al, 2010;Liu, 2005;Lofi et al, 2012;Lubbe and Worthington, 2006;Majer et al, 1997;Pytharouli et al, 2011;Queen and Rizer, 1990;Robinson et al, 2013;Schmutz et al, 2011;Tsoflias and Hoch, 2006;Talley et al, 2005;Wishart et al, 2008]. Here, we focus on the electrical resistivity method for the reasons that (i) a large body of previous work has indicated that the presence of fractures commonly has a significant influence on field geoelectrical measurements, especially as a function of direction or azimuth, and thus that these measurements may contain important information regarding the fracture distribution [e.g., Boadu et al, 2005;Busby, 2000;Lane et al, 1995;Taylor and Fleming, 1988]; (ii) geoelectrical measurements can be acquired in a straightforward manner along the Earth's surface and/or from boreholes in order to estimate the distribution of subsurface electrical resistivity at a range of spatial scales; and (iii) the presence of fractures in a rock represents preferential pathways for the flow of both water and electric current, which suggests that hydraulically relevant information on fracture network properties may be obtained from geoelectrical data.…”