Tsunami deposits in a lacustrine sequence of the Sanriku coast

湖相沉积序列中的海相砂层，连同砂层内的间隙碳酸盐和富含海水成分的孔隙水，是形成海啸沉积的明显证据。在三陆海岸的池塘沉积物中发现了13层薄砂层。详细的沉积学和地球化学工作表明，砂层是海啸形成的。这些海啸沉积物的年代大多与史料记载的中重度古海啸的年代相当，说明在海岸上波浪最高高度达到1米以上的海啸造成净沉积物向陆地输送，并在池塘中积累了薄砂层。评估海啸对沿海地区的潜在危害尤为重要，准确了解破坏性海啸的发生频率对于评估沿海核电站等高风险设施的水利工程安全至关重要。迫切需要更多地了解俯冲带内及其周围的地震起源。这里采用的方法可应用于活动边缘的其他沿海地区，并可提供有关海啸风险的有用信息。

Marine sand layr in a succession of lacustrine deposits, together with interstitial carbonates and pore water rich in seawater ingredients within sand layr, is distinct evidence for tunami-genic sedimentation. Thirteen thin sand layrs were found to be intercalated within pond deposits of the Sanriku coast. Detailed sedimentological and geochemical work demonstrates that the sand layr were laid down as a result of tsunamis. The dates of these tsunami deposits are mostly equivalent to the ages of the moderate to severe ancient tusnamis documented in historical materials, suggesting that tsunamis with waves having reached a maximum height of more than 1 m on the coast caused net sediment tranbsport landward and accumulated thin sand beds in the pond.The estimation of potential hazards to coastal zones afforded by tsunamis is especially important, and an accurate knowledge of the frequency of destructive tsunamis is essential for assessment of the hydro-engineering security of high risk facilities such as coastal nuclear power stations. There is a pressing need for learning more about earthquake initiation in and around subduction zones. The methods adopted here can be applied to other coastal areas in the active margin, and may provide useful information on the risks of tsunamis.