Fig. 5

Schematic model for the relationship between the electrical resistivity structure and local seismicity. a Interpretation of the resistivity structure in terms of fluids and isotherms. Red areas indicate relatively low-resistivity zones. Red and blue arrows represent hot- and cold-fluid movements, respectively. Large and small crosses show the hypocenters of large and small earthquakes, respectively; large earthquakes tend to initiate along the outer edge of the low-resistivity zones. b Schematic model for rupture initiation and its propagation outward from the outer edge of a low-resistivity zone. From left to right, the three figures represent the temporal evolution of rupture propagation. The model is based on the hypothesis that the pre-failure pressure/temperature (PT) gradient (spatial difference) of the pore fluids contributes to crack propagation and coalescence. One possible mechanism for crack coalescence is shown here. The solid arrows indicate the slip directions and the opening of the tensile crack. The spatial difference in the pre-failure pore-fluid pressure tends to both promote fluid movement (red arrow) and enhance outward rupture propagation (open arrow) from the low-resistivity zones. Note that the direction of rupture growth is constrained by both the orientation of the crack that initially slipped and the regional stress field