Logarithm of fracture energy ( E
) plotted against normal stress. Fracture energy represents a part of the frictional work that occurs during slip weakening over a characteristic distance (Dc), which is defined by the shaded area under a shear stress versus displacement curve (inset). Dc was calculated by fitting data with an empirical exponential equation (Mizoguchi et al. 2007) (red dashed curve). Data for Cores 38 and 40 from Site 436 are shown as blue and red circles, respectively. Also shown are the fracture energy of the plate boundary fault from the Japan Trench (Ujiie et al. 2013), the Nojima fault gouge (Mizoguchi et al. 2007; Sawai et al. 2012), kaolinite-bearing gouge from the Median Tectonic Line (Brantut et al. 2008), and talc gouge (Boutareaud et al. 2012), as determined under similar experimental conditions to those of the present study.