Fig. 4

Plot of the characteristic distance Δr _c as a function of mainshock magnitude m for seismicity prior (circles) and subsequent (diamonds) to mainshocks in Japan. The Kumamoto earthquakes (see also Fig. 5) are shown as a set of data of prior and subsequent seismicity as follows: blue line segment from m6.5 to 7.3 with a blue circle, indicating seismicity during a 3-year period prior to the M6.5 shock; blue line segment from m6.5 to 7.3 with a blue diamond, indicating seismicity subsequent to the M7.3 shock. As a reference, data for seismicity in the period subsequent to the M6.5 shock until the M7.3 shock are included (red diamond). Thin solid line is drawn by using extrapolation from the scaling (thick solid line) of the characteristic asperity radius l _a with m of 6.6 to 9.2, based on Somerville et al. (2015). Thin dashed lines are drawn by using extrapolation from the one-standard-deviation limits (thick dashed line). The inset shows a plot of ρ(Δr) as a function of Δr from the mainshock with m = 4 ~ 5 for seismicity prior (circles) and subsequent (diamonds) to mainshocks. Data are fitted with ρ(Δr) ~ Δr ^−η with η = 1.35. The deviation point, below which an inverse power law is no longer valid, is marked by Δr _c