Historical and Prehistorical Large Tsunamis in the Southern Ryukyus, Japan

Source Fault Model of the 1771 Yaeyama Tsunami, Southern Ryukyu Islands, Japan, Inferred from Numerical Simulation

“…Model F1 describes a reverse fault located to the southeast of Ishigaki Island (area A in the Fig. 1), corresponding to the source area estimated by previous studies (HATORI, 1988;NAKATA and KAWANA, 1995). The geometry of the fault was set as follows: / = 80°, d = 70°, k = 90°, L = 66 km, W ¼ 33 km, average slip of 8 m, and seismic moment of 5.2 · 10 20 N/m 2 (M w = 7.8).…”

“…5). This corresponds to the distribution of tsunami boulders, which were carried by the Yaeyama tsunami or prehistorical tsunamis (KATO et al, 1988;NAKATA and KAWANA, 1995). The computed inundation area corresponds to the recorded one which is traced using the historical record, tsunami boulders, and damaged shrines at the south of Ishigaki Island.…”

“…Later large tsunami struck the same area, reaching a maximum height exceeding 30 m on the southeastern side of Ishigaki Island ( Fig. 1) (NAKATA and KAWANA, 1995). The damage area was distributed between Ishigaki Island and Miyako Island, resulting in significant damage and approximately 12,000 casualties.…”

“…Numerous simulations have been conducted for this tsunami, and the source models employed can be broadly classified into seismological fault models (NAKATA and KAWANA, 1995), submarine landslide models (HIYOSHI et al, 1986), and faultand-landslide models (HIRAISHI et al, 2001;IMAMURA et al, 2001). In the seismological fault model, the fault is set to the southeast of Ishigaki Island (area A in Fig.…”

“…1). In order to verify whether this model is correct, marine surveys have been (HATORI, 1998;NAKATA and KAWANA, 1995). Hatched areas (B and C) denote the locations of the submarine landslide estimated in marine surveys (MATSUMOTO and KIMURA, 1993;MATSUMOTO et al, 2001) and the previous tsunami simulations (IMAMURA et al, 2001), respectively.…”