Two-dimensional resistivity structure of the fault associated with the 2000 Western Tottori earthquake

Abstract

Two-dimensional resistivity surveys were carried out along two profiles that were laid across earthquake faults initiated by the 2000 Western Tottori earthquake. One profile was located 7 m from a trenching pit, thereby enabling a direct comparison of resistivity cross-section with the geological cross-section and, subsequently, a precise interpretation of the resistivity structure. Features of the resistivity cross-section were found to correspond fairly well to the geological cross-section. A clear resistivity boundary between the resistive and conductive zones matches the earthquake fault that was found by the trenching survey. Variations in resistivity depend primarily on the development of fractures. Two types of conductive zones were found: (1) a clear and deep-rooted conductor that corresponds to an earthquake fault and (2) an indistinct and spatially localized conductor that corresponds to a fracture attributed by landslides and collapse. A few weak conductive zones that match with discrete earthquake faults characterize our resistivity model. This feature is different from the resistivity cross-sections found at the Nojima and Ogura Faults that appeared at the time of the 1995 Hyogo-ken Nanbu earthquake; these two latter faults are characterized by distinct single conductive zones. Based on geomorphological, geological, and seismological evidence, the earthquake fault of the 2000 Western Tottori earthquake can be classified as an immature fault. In contrast, the Nojima and Ogura Faults have been active for at least the entire Quaternary period. We conclude that the difference in the fault development stages is reflected in their different resistivity structures.

Role of H₂O in Generating Subduction Zone Earthquakes

“…H 2 O thus derived from the slab rises and finally penetrates into the fault zones in the upper crust where historic great earthquakes have occurred on high-angle reverse faults that are unfavorably oriented for failure (Wannamaker et al, 2009). Similar low resistivity zones distributed in the lower crust below faults have also been found in many areas around the world, including the North Anatolian fault, the San Andreas fault and the 2000 Western Tottori earthquake fault (e.g., Mitsuhata et al, 2001;Ogawa and Honkura, 2004;Tank et al, 2005;Yamaguchi et al, 2007;Becken et al, 2008). Seismic tomography seems to show further evidence of aqueous fluids that have migrated upward and infiltrated from the highly overpressured lower crust into the seismogenic fault zone in the upper crust.…”

Helium isotopes as a tool for detecting concealed active faults

“… Inoue et al [2002] stated that these are “immature faults” on the basis of the short fault lengths with narrow fracture zones. Seismic and geoelectric evidence [ Fukuyama et al , 2003; Yamaguchi et al , 2007], and the results of sandbox analog experiments [ Ueta et al , 2000] suggest that these faults are in an early stage of fault development. In addition, simulation by Dalguer et al [2003] indicated that shear slip occurring on a preexisting fault at least at a depth of 2.0 km could cause the generation of surface raptures under a tensile stress regime around the aftershock region, consistent with the field observations.…”

Low resistivity and permeability in actively deforming shear zones on the San Andreas Fault at SAFOD

“…[], Chelungpu fault, Chi‐Chi earthquake, Taiwan; Yamaguchi et al . [], western Tottori earthquake, Japan; and Wannamaker et al . [], Alpine fault, New Zealand).…”

“…Numerous resistivity studies have been conducted on active fault zones around the world (see for instance, Yamaguchi et al [2001] and Pezard et al [2000], Hyogo-ken Nanbu (Kobe) earthquake, Japan; Hung et al [2007] and Yang et al [2002], Chelungpu fault, Chi-Chi earthquake, Taiwan; Yamaguchi et al [2007], western Tottori earthquake, Japan; and Wannamaker et al [2002], Alpine fault, New Zealand). The resistivity structure of various sections of the San Andreas Fault in California, have been modeled by Mazzella [1976], Phillips and Kuckes [1983], Unsworth et al [2000], Unsworth and Bedrosian [2004], and others.…”