## 3 Strong Ground Motion Prediction of the Nankai-Trough Earthquake
### Waveform Synthesis and Its Validation
Although it is difficult to consider nowadays to have an independent rupture at the Tokai segment before the Tonankai and Nankai earthquakes, the Tokai segment had been considered to rupture as an independent Tokai earthquake within the foreseeable future in the 1970s based on the slip deficit in the segment (e.g., Ishibashi, 1981 [31]). Therefore, the Central Disaster Management Council (CDMC), Cabinet Office of Japan, had been evaluating strong ground motions based on the hypothesized Tokai earthquake as an independent event until recently. We adopted the fault rupture scenario proposed by CDMC [32] and used the same method as the Tonankai earthquake described above to calculate strong-motion waveforms. Figure 6 shows a comparison of the synthetic PGAs or PGVs calculated for the hypothesized Tokai earthquake with GMPE by [PERSON] and [PERSON] [10] as in Figure 4. Furthermore, Figure 7 shows a comparison of seismic intensity scales estimated from the synthetic strong ground motions of the Tokai earthquake and the estimated seismic intensity scale of the 1854 Tokai earthquake (stars), which ruptured much larger areas including (but not limited to) the Tokai segment. Again, correspondence of the synthetic strong motions with the empirical prediction by GMPE as well as the intensity estimated for the previous earthquake is fairly good. Figure 5: A comparison of the seismic intensity scale distribution of strong ground motions calculated from the hypothesized Tonankai earthquake in this study (top) and that of the estimated ones from the damage survey of the 1944 Tonankai earthquake according to HERP (bottom). Figure 6: Peak ground acceleration and velocity from a hypothesized Tokai earthquake by the statistical [PERSON]’s function summation method of this study (symbols) and by the GMPE of [PERSON] and [PERSON] [10] as a function of the shortest distance to the fault. Figure 7: A comparison of the seismic intensity scale distribution of strong ground motions calculated from the hypothesized Tokai earthquake in this study (top) and that of the estimated ones (\(\star\)) from the damage survey of the 1854 Ansei Tokai earthquake (bottom). Squares in the bottom panel indicate the same results as in Figure 5 (bottom), based on the numerical calculation for the Tonankai earthquake according to HERP and so we should not refer to them for the Tokai earthquake simulation. Please note that the map scales are different. The strong ground motions of the hypothesized Nankai earthquakes had been predicted by [PERSON] and [PERSON] [17] in which they used the same statistical [PERSON]'s function and summation method shown in the previous section. Figure 8 shows the fault model of [PERSON] and [PERSON] [17] and Figure 9 shows the comparison of the synthetic PGAs or PGVs calculated for the hypothesized Nankai earthquake with GMPE by [PERSON] and [PERSON] [10] reproduced from [PERSON] and [PERSON] [17]. Finally, we considered here a consecutive rupture scenario of all the three segments along the Nankai Trough, namely, Tokai, Tonankai, and Nankai segments, as a hypothesized worst-case scenario. Here, the calculated strong ground motions from each earthquake were superimposed along with the time history, while considering the delay in the rupture start time of each segment by assuming the constant rupture velocity of 2.7 km/s between the next rupture initiation point and the closest point of the adjacent segment already ruptured. Figure 10 shows a comparison between PGA or PGV calculated for the whole earthquake scenario along the Nankai Trough and the GMPE by [PERSON] and [PERSON] [10]. Figure 11 compares the seismic intensity scales converted from the synthesized waveforms of this study and the seismic intensity distribution from the similar whole earthquake scenario calculated by the Central Disaster Management Council [7].