In western Japan, large earthquakes often take place in the crust of the overlying Eurasian plate. These events occur widely in the forearc and back-arc areas, and close to the volcanoes along the volcanic front, similar to those in NE Japan (e.g., Zhao, 2015). A typical large crustal earthquake in western Japan is the 1995 Kobe earthquake (M 7.2). Zhao et al. (1996) determined 3-D Vp, Vs and σ images of the Kobe source zone and revealed a low-V and high-σ anomaly in the lower crust below the Kobe hypocenter at ~17 km depth. This anomaly was interpreted as a fluid-filled, fractured rock matrix that triggered the Kobe mainshock. Later studies have shown that the fluids at the Kobe hypocenter originated from the dehydration reactions of the subducting PHS slab (Zhao et al., 2002; Salah and Zhao, 2003b; Tong et al., 2011).
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