Fig. 1

a Location map of southwestern Japan showing the study area (black rectangle; Figs. 5, 6, 7, 8) and the array network (red square). Gray dots are tremor hypocenters from the NIED hybrid clustering catalog. Contour lines represent the depth of the Moho in the subducting Philippine Sea plate (Shiomi et al. 2008). Dotted square represents the area shown in (c). b Configuration of stations (triangles) in the seismic array. The black triangle is the central station. c The distribution of short-term SSEs detected geodetically by GSJ and/or NIED during the study period. Gray rectangles are surface projections of areas on the fault planes of the short-term SSEs; the black side of each rectangle is the up-dip edge. Yellow triangle represents a Hi-net station (KRTH) for which tilt data are shown in Fig. 4b. d Space–time plot of tectonic tremors from the NIED hybrid clustering catalog. Distance along strike or along dip is measured from the corner with a black circle of the black rectangle in (a). Circles represent hypocenters of tremor clusters for different ETS events analyzed in this study, colored according to their ETS number. ETS events 1, 8, and 11 were excluded from further analysis. Gray dots are tremor hypocenters that are isolated or belong to small ETS events. Gray vertical bars represent short-term SSEs detected geodetically by GSJ