Fig. 4

a Cumulative slips in simulated Nankai Trough seismic cycles with the M _w 7 patches of Hyuga-nada and the Bungo channel. Each colored cumulative slip profile is evaluated for the cross of the same color shown in Fig. 2. Solid and open stars near the steps of the red line denote large (M _w > 8.5) and small (M _w < 8.5) Nankai Trough earthquakes, respectively. Except for the earthquake steps around time =1310 years, large and small Nankai Trough earthquakes occur alternately; large Nankai Trough earthquakes are accompanied by about 10 m of slip at Kumano-nada (larger steps in red line) and more than 10 m of slip off Ashizuri (larger steps in green line). Except for the small event at time =1310, small Nankai Trough earthquakes have smaller slips than the large earthquakes at both Kumano-nada and off Ashizuri, although the magnitude relationship of the slips between Kumano and Ashizuri is the reverse of that of the large earthquakes. At Hyuga-nada, more than 5 m of slip always occur with the occurrences of large earthquakes, whereas with the small earthquakes, the slips vary from 0 to about 5 m. In addition, as for the Hyuga-nada earthquakes (M _w ~ 7.5), several slip events at Hyuga-nada occur independently of the Nankai Trough earthquakes. b Close-up view of broken rectangle in (a). A Hyuga-nada earthquake triggers a Nankai earthquake, then a Tokai earthquake occurs with a time lag of 1 year