Historical and paleo-tsunami deposits during the last 4000 years and their correlations with historical tsunami events in Koyadori on the Sanriku Coast, northeastern Japan
Historical and paleo-tsunami deposits during the last 4000 years and their correlations with historical tsunami events in Koyadori on the Sanriku Coast, northeastern Japan
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DOI：
10.1186/s40645-015-0047-4
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发表时间：
2015-06-27
影响因子：
3.9
通讯作者：
Miyauchi, Takahiro
中科院分区：
文献类型：
--
作者：
Ishimura, Daisuke;Miyauchi, Takahiro
在过去的几百年里，沿着日本东北部太平洋沿岸的三陆海岸发生的大海啸已经被记录和观察到。然而，像2011年太平洋沿岸东北地震引发的海啸那样的大型海啸的风险无法从以前的研究中进行评估，因为这些研究缺乏海岸线上历史和古海啸沉积物的证据。因此，我们首先通过对日本东北部三陆海岸Koyadori海岸沼泽的挖掘调查，确定了事件沉积物，这是海啸沉积物的候选者。其次，我们确定了沉积物的物理化学性质（颗粒的圆度、颜色、干湿密度和着火损失），并通过放射性碳定年和tephra分析确定了它们的地质年代。第三，根据事件沉积物的沉积特征和成因、沉积环境、古海岸线和土地所有者访谈，将事件沉积物确定为海啸沉积物。本文报道了近4000年来的11个海啸沉积（E1- e11），其中E1、E2、E3和E4分别与2011年的东北海啸、1896年的明治三陆海啸、1611年的庆町三陆海啸和869年的佐干海啸相关。根据年龄数据和海沟中海啸沉积物的数量，我们估计比1896年明治三陆海啸更大的海啸平均每290-390年发生一次，袭击研究区域。然而，历史海啸相关性揭示了海啸发生的变化，表明海啸产生的多样性和/或日本海沟周围不同来源的几种大地震的组合。
Large tsunamis occurring throughout the past several hundred years along the Sanriku Coast on the Pacific coast of northeastern Japan have been documented and observed. However, the risk of large tsunamis like the tsunami generated by the 2011 off the Pacific coast of Tohoku earthquake could not be evaluated from previous studies, because these studies lacked evidence of historical and paleo-tsunami deposits on the coastline. Thus, we first identified event deposits, which are candidates for tsunami deposits, from excavating surveys conducted on the coastal marsh in Koyadori on the Sanriku Coast, northeastern Japan. Second, we determined the physicochemical sediment properties of the deposits (roundness of grains, color, wet and dry densities, and loss on ignition) and established their geochronology by radiocarbon dating and tephra analysis. Third, we identified event deposits as tsunami deposits, based on their sedimentary features and origin, sedimentary environment, paleo-shoreline, and landowner interviews. In this study, we report 11 tsunami deposits (E1-E11) during the past 4000 years, of which E1, E2, E3, and E4 were correlated with the 2011 Tohoku-oki tsunami, the 1896 Meiji Sanriku tsunami, the 1611 Keicho Sanriku tsunami, and the 869 Jogan tsunami, respectively. From age data and the number of tsunami deposits in the trench, we estimated that tsunamis larger than the 1896 Meiji Sanriku tsunami occur and hit the study area on average every 290-390 years. However, historical tsunami correlations revealed variable tsunami occurrence, indicating diverse tsunami generation and/or the combination of several types of large earthquakes from different sources around the Japan Trench.