Not all faults are conductive: the effects of seasonal weather changes on the near‐surface expression of faults

ABSTRACT The near‐surface electrical properties of faults can change with seasonal climate, depending on the nature of the materials filling the faults, e.g. fault gouge vs fractured rock, and be subject to seasonal weather changes. A period of dry weather, especially in a hot climate, can dry out the near‐surface sections of faults that are filled with porous materials, thus increasing the electrical resistivity, yet may not affect a fault that is filled with fine‐grained material that retains moisture well. Conversely, a sustained period of wet weather can fill porous faults with water, thus decreasing the resistivity. To illustrate the impact of seasonal weather changes on the near‐surface properties of faults, we conducted electrical imaging and ground‐penetrating radar surveys during the late spring, summer, and early autumn on the Glen Lyon and Benmore segments of the Ostler Fault, respectively, in the South Canterbury and Central Otago provinces of the South Island of New Zealand. The changes in the response are clear: seasonal weather changes can affect the near‐surface properties of faults, and the geophysical responses from the near‐surface faults can vary depending on the nature of the material filling the fault.