Geochemical and mineralogical data showing transformation of Ca-smectite into illite in the fault gouge. Modified from Yamaguchi et al. (2011b). See Figure 2 for the location of the fault gouge. (a) Photograph of the fault gouge in the megasplay fault zone showing the XRF mapping area in (b) (white rectangle). Red triangles indicate fault gouge (upper) and fragmented gouge (lower) in microbreccia. (b) Compositional maps across fault gouges (solid triangles). (c) XRD patterns for fault gouge and microbreccia shown in (a).