Fig. 1

a Distribution of stations and tremor events catalogued in this study. Blue, light coral, light green, and dark green dots represent the labeled tremor events in the three sub-areas of western Shikoku (western, central, and eastern sub-areas) and eastern Shikoku, respectively (Areas A to D). The colored lines indicate different divisions: Obara (2010) in black, Kano et al. (2018) in yellow, and this study in red. b The number of tremor event along the longitude. c The depth distribution of tremor events along the longitude. Events belong to four different areas are denoted by different colors