Fig. 1

Geological setting of the MTL and locations of the investigation sites. a The tectonic setting of the Japanese Islands; b geological map of the northwestern Shikoku Island; c locations of drilling and trench sites. The geological map was modified from a seamless digital geological map of Japan (1:200 000) edited by the Geological Survey of Japan (2017). Active fault data were compiled from Nakata et al. (1998), Goto et al. (1998), and Tsutsumi et al. (1998). The shaded relief map was created using a 5-m DEM obtained from the Geospatial Information Authority of Japan.