Characterizing water-level changes due to fracturing generated by the strike-slip fault of the 12 November 1999, Düzce, Turkey, earthquake using the VLF method

The devastating Düzce earthquake occurred on 12 November 1999 in Turkey, and caused groundwater pollution by damaging sewer systems in populated areas as well as pipelines and chemical plants. Leakage from these sources of pollutants advected and diffused along the hydraulic gradient enhanced by the surface rupture. We constructed a conceptual model to identify the flow system within and near the ruptured zone in the devastated town of Kaynaşli by utilizing the very low-frequency electromagnetic induction (VLF) and dc-resistivity methods ten days after the earthquake. Void volume increase due to fracturing from the surface to a depth of several meters caused gravity-driven drainage to form a dewatered zone near the surface. This downward flow filled the fractures beneath the dewatered zone and caused an increase in volumetric water content. The measured apparent dc-resistivity profile with an electrode spacing of 5 m showed an increasing resistivity over the dewatered zone. The measured VLF profile, on the other hand, showed a characteristic behavior with decreasing resistivity corresponding to a depth where volumetric water-content increase is expected to occur.