Fig. 3

Hypocenter and origin time of the triggered event estimated by the back-projection method. a Areas used for the multi-scale analysis. A yellow star indicates the epicenter of the mainshock. White triangles indicate stations used in the analysis. b Epicenter of the triggered event obtained from multi-scale analysis. Color at each grid indicates the maximum stacked amplitude within the time range in Table 1. A red and a dashed red circles indicate the optimal and the suboptimal result for the epicenter of the triggered event, respectively. Panels show results for the distribution of the stacked amplitude for spatial grid intervals of 0.1°, 0.05°, 0.025°, and 0.0125°. Each panel shows the distribution at the depth of the optimal result. c Distribution of the stacked amplitude at an elapsed time of 33.3–34.0 s from the origin time of the mainshock. The distribution shows the result for the grid interval of 0.0125° at the depth of 5 km. d Distribution of the maximum stacked amplitude within the time range for the grid interval of 0.0125° at each depth