Fig. 2
a Temporal variations of the RTM (black), R (blue), T (green), and M (red) at the point indicated by a cross in b. Red arrows show the moments of the 2015 Off Satsuma Peninsula earthquake and the mainshock of the 2016 Kumamoto earthquakes; both epicenters are indicated by stars in b. b Areas of seismic quiescence before the two earthquakes (stars). The figure, generated by a grid with 0.1° × 0.1° spacing, shows the most quiescent period on October 1, 2015, indicated by a black arrow in a (45 days before the 2015 Off Satsuma Peninsula earthquake). The cross is the point of time variation shown in a. Parameters used were R 0 = 100 km, R max = 200 km, T 0 = 1 year, T max = 2 years, and M min = 2 (Table A1 in Additional file 1). For parameter definition, see Nagao et al. (2011)