Fig. 5

a Magnitude–time plot for the M ≥ 1 earthquakes in the Wakayama swarm. The blue vertical line denotes the timing of the 2011 Tohoku–oki earthquake. b Cumulative number of M ≥ 1 earthquakes (red line). The black dashed line denotes an average seismicity rate of 2.3 earthquakes per day (15,256 earthquakes over the 18-year analysis period). Vertical lines indicate when the M ≥ 4 earthquakes occurred in the swarm. c Cumulative number (ΔN) of M ≥ 1 earthquakes deviated from the average seismicity rate. It is noted that ΔN becomes zero at both ends of the analyzed period