ELUCIDATION OF SEDIMENT TRANSPORT AND ENVIRONMENTAL MODIFICATION BY TSUBNAMIS

日本东北部弧前地区是地震活动广泛、海啸产生的地体，面向太平洋的沿海地区曾多次遭受海啸袭击。 869年7月13日，一场由大地震引发的海啸袭击了沿海地区，导致平原上大量沉积了精选的细沙。沉积学分析和水动力模型表明，沙层是由第一波海啸形成的，我们得出结论，低洼沿海地区在海啸爆发期间容易遭受大面积洪水的影响。沿海序列中按时间顺序记录了较早的海啸大规模入侵的痕迹，这表明日本东北部沿海平原在不久的将来面临海啸灾害的危险。日本东北部太平洋沿岸因海啸的反复入侵而臭名昭著。然而，自城岩事件发生以来，仙台平原并未受到大海啸的影响。快速城市化已向沿海地区推进。必须认识到，如果人口稠密海岸的海啸减灾工作要取得成功，就迫切需要了解潜在海啸发生的时间和规模。阐明常岩海啸在区域范围内广泛入侵的原因和影响，不仅对于预防灾害至关重要，而且对于了解前弧的构造过程也至关重要。本研究利用沉积学分析和水动力模型对常岩海啸沉积物进行了研究，试图阐明波浪穿透海岸线以外4公里以上的机制。自日本东北部开始科学观测以来，已经过去了100多年，在此期间从未观测到超出海岸线2公里以上的海啸淹没距离。据历史文献推测，常岩海啸造成的海水淹没已达到距海岸4公里以上的内陆地区。海水的深入渗透意味着将发生前所未有的大规模海啸。较少的

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