ELUCIDATION OF SEDIMENT TRANSPORT AND ENVIRONMENTAL MODIFICATION BY TSUBNAMIS

日本东北部的弧前地区是地震活动和海啸生成的多发地带，面向太平洋的沿海地区多次遭受海啸袭击。公元869年7月13日，大地震引发的海啸侵袭了沿海地区，导致平原上大量分选良好的细沙沉积。沉积学分析和水动力学模型表明，砂层是由海啸的第一波，我们的结论是，低洼的沿海地区容易受到广泛的洪水在海啸助跑。在海岸序列中，以一定的时间间隔记录了大规模海啸入侵的痕迹，我们指出，日本东北部的沿海平原在不久的将来是海啸灾害的危险。日本东北部的太平洋海岸是臭名昭著的海啸的反复入侵。然而，仙台平原自2004年发生海啸以来， 关于我们 Jogan事件城市化迅速向沿海地区推进。必须认识到，如果要在人口稠密的沿海地区成功地减轻海啸影响，就迫切需要了解潜在海啸发生的时间和规模。阐明常感海啸区域性大规模入侵的原因和影响，不仅对于预防灾害，而且对于了解弧前构造过程也是必不可少的。本研究利用沉积学分析和水动力学模型对常观海啸沉积物进行了研究，试图弄清波浪在海岸线外4 km以上的穿透机制。从日本东北部开始进行科学观测到现在已经过去了100多年，在这段时间里从未观测到海啸在海岸外2 km以上的淹没距离。从历史文献中可以推断出，常观海啸造成的海水淹没范围从海岸线向内陆延伸了4公里以上。海水的深入意味着前所未有的大规模海啸的发生。少

The fore-arc region of northeast Japan is a terrane of extensive seismic activity and tsunami generation, and the coastal areas facing the Pacific Ocean have been repeatedly attacked by tsunamis. On July 13,869 a tsunami triggered by a large-scale earthquake invaded the coastal zones, causing extensive deposition of well-sorted fine sand over the plains. Sedimentological analysis and hydrodynamic modeling indicate that the sand layer was developed by the first wave of the tsunami, and we conclude that low-lying coastal zones are susceptible to extensive flooding during tsunami runup. Traces of large-scale invasion by older tsunamis are recorded in the coastal sequences at regular chronological intervals, and we indicate that the coastal plains of northeast Japan are in danger of tsunami disasters in the near future.The Pacific coast of NE Japan is notorious for the repeated invasion of tsunamis. The Sendai plain, however, has not been affected by a large tsunami since the occurrence of … More the Jogan event. Rapid urbanization has advanced to the coastal areas. It must be recognized that understanding of the timing and scale of potential tsunami occurrence is an urgent requirement, if tsunami mitigation efforts on the densely populated coast are to be successful. The elucidation of the cause and effect of regionally extensive invasion of the Jogan tsunami is indispensable not only to prevent a disaster but also to gain an understanding of tectonic processes of the fore arc. In this study, the Jogan tsunami deposits were studied using sedimentological analyses and hydrodynamic models in an attempt to make clear the mechanism of wave penetration more than 4 km beyond the coastline.More than 100 years have passed since the beginning of scientific observation in NE Japan, and inundation distance of tsunamis exceeding 2 km beyond the shore was never observed during this time interval . It is inferred from the historical documents that seawater inundation by the Jogan tsunami reached 4 km or more inland from the coast. The deep penetration of seawater mean an occurrence of unprecedented large-scale tsunami. Less