한반도 남해에 도달한 1707 일본 호에이 지진 지진해일의 재구성

Abstract

The 11 March 2011 Tohoku, Japan, tsunami reached the coast of Jeju Island, the southernmost Korean Peninsula, after about five hours from the origin time of the earthquake. The island is located in the backside of the epicentral Pacific region, and the direct propagation path is blocked by the Japanese Islands Arc. It implies that the tsunami observed in the Jeju Island is diffracted waves. The wave height observed in the island reaches about 0.2 m. There is no report of damage caused by the tsunami. On the other hand, there is a historical document which records an observation of earthquake and tidal waves simultaneously in the island. The date corresponds to the occurrence of the great 1707 Hoei earthquake (M~9) and tsunami in the Nankai and Tonankai areas, the offshore southern Honshu, Japan. The propagation path to the island of the Hoei tsunami is similar to that of the Tohoku tsunami, but is much shorter than it. In this study, we try to show that the 1707 historical observations in the Jeju Island was resulted from the great Hoei earthquake and tsunami in Japan, and how the maximum wave height was. Numerical simulations and investigations of historical documents are performed in parallel for this purpose. We assume that the source information of the 2011 Tohoku earthquake would be comparable to the 1707 Hoei earthquake because of the similar magnitude and tectonic environment. Therefore numerical simulations employ a variety of fault rupture models which are determined for the 2011 Tohoku earthquake. We compare results of tsunami simulations for three finite-fault models which are determined for the 2011 Tohoku, Japan, earthquake; USGS (Hayes, 2011), UCSBI, and UCSBIII (Shao et al., 2011). Also we reconstruct static displacement models which correspond to each finite-fault model and compare the effects of them to those of the finite-fault models. Heights and arrival times of tsunami waveforms which are generated from six models are compared with observations at three DART buoys which are located in the Pacific ocean. The results show that the UCSBIII model most accurately reproduces the observed tsunami waveform. Overall the finite-fault models give much better results than the static displacement models. On the basis of these results, we apply the UCSBIII finite-fault model to the 2011 Tohoku earthquake for reproducing the tsunami observation in Jeju island. The result show that tsunami waves tends to diffuse between Jeju island and Kyusyu island. For reproduction of tsunami observation in Jeju island from the 1707 Hoei earthquake, we employed a static displacement model made by An'naka et al. (An'naka et al, 2003). The result shows negligible tsunami heights in Jeju island, which seems to state contradiction to the historical tsunami observation in the island. However, there is another possibility that if we can utilize a virtual finite-fault model for the Nankai trough area in the future, we might obtain more plausible result of tsunami waves in Jeju island. Therefore, this study may extend to the prediction of any future tsunami in the island due to the potential megathrust earthquake which is expected to be co-located with the 1707 Hoei earthquake.