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多发地区，面向太平洋的沿海地区多次遭受海啸袭击。13869年7月，一场由大规模地震引发的海啸袭击了沿海地区，在平原上造成了大量分类良好的细沙沉积。沉积学分析和水动力模拟表明，沙层是由海啸第一波形成的，我们得出结论，低洼沿海地区在海啸上升期间容易发生大面积洪水。古海啸大规模入侵的痕迹以一定的时间间隔记录在沿海序列中，表明日本东北部沿海平原在不久的将来将面临海啸灾害的危险。日本东北部的太平洋沿岸因屡次发生海啸而臭名昭著。仙台平原，然而，没有受到大海啸的影响，因为发生了……快速城市化已向沿海地区推进。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，就迫切需要了解潜在海啸发生的时间和规模。阐明约干海啸区域大范围侵入的原因和影响，不仅对预防灾害，而且对了解弧前的构造过程都是必不可少的。本研究利用沉积学分析和水动力模型对佐干海啸沉积物进行了研究，试图弄清波浪在海岸线外4公里以上的穿透机制。在日本东北部进行科学观测已有100多年，在这段时间内从未观测到超过海岸2公里的海啸淹没距离。从历史文献中可以推断，佐干海啸造成的海水淹没达到了离海岸4公里以上的内陆。海水的深度渗透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