Deposition of sediments of diverse sizes by the 2011 Tohoku-oki tsunami at Miyako City, Japan
Deposition of sediments of diverse sizes by the 2011 Tohoku-oki tsunami at Miyako City, Japan
复制标题
2011 年东北冲海啸在日本宫古市沉积的不同大小的沉积物
DOI：
10.1016/j.margeo.2014.05.019
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发表时间：
2014
期刊：
影响因子：
2.9
通讯作者：
K. Goto
中科院分区：
文献类型：
--
作者：
M. Yamada;S. Fujino;K. Goto
本文报道了2011年在日本宫古市发生的东北海啸对各种大小的沉积物的运输和沉积，从泥浆到巨石，海啸在海岸达到海平面28.1米，内陆被淹没1750米。泥到鹅卵石大小的沉积物形成了层状沉积物，覆盖了原来是稻田的低地。这些层状沉积物在海滩附近非常厚（约0.5 ~ 1.0 m），主要由砾石组成，在内陆通常变薄变细，形成几厘米厚的砂泥沉积物。除了层状沉积物外，在低地还发现了许多由海啸屏障碎片和其他结构、消波块和火山岩组成的巨石，主要有三组。在距海岸线750 m处，砾石尺寸急剧减小，层状沉积物的厚度和粒度也急剧减小。这些发现表明，受当地地形的限制，波流速度的突然减速导致了那里的层状沉积物和巨石的快速沉积。有趣的是，这些巨石沉积在分层沉积物的顶部，而不是埋在其中。这一发现表明，砂和砾石在第一波的钻孔前被搬运，并在巨石到达之前沉积。大型巨石周围向海延伸的冲刷表明，尽管反冲流在一定程度上侵蚀了层状沉积物，但这些巨石并没有受到反冲流的移动。因此，层状沉积物和巨石之间的地层关系表明，它们都可能是由第一波沉积的。
This paper reports the transport and deposition of sediments of various sizes, ranging from mud to boulders, by the 2011 Tohoku-oki tsunami at Miyako City, Japan, where the tsunami reached 28.1 m above sea level at the coast and inundated up to 1750 m inland. Mud- to cobble-sized sediments formed layered deposits that covered the lowland where paddy fields had been. These layered deposits were remarkably thick (> 0.5–1.0 m) near the beach, where they were composed mainly of gravels, and they generally thinned and fined inland to sand and mud deposits a few centimeters thick. Separate from the layered deposits, many boulders, consisting of fragments of the tsunami barrier and other structures, wave-dissipating blocks, and volcanic rocks, were found on the lowland, mainly in three clusters. Boulder size decreased abruptly about 750 m inland from the shoreline, where the thickness and grain size of the layered deposits also showed a sharp decrease. These findings suggest that a sudden deceleration of the wave flow velocity, constrained by the local topography, caused rapid deposition of both the layered deposits and boulders there. Interestingly, the boulders were deposited on top of the layered deposit, not buried within it. This finding suggests that sand and gravel were transported in the bore front of the first wave and deposited before the arrival of the boulders. Seaward-extending scours around large boulders showed that the boulders were not moved by the backwash flow, although the backwash eroded the layered deposits to some extent. The stratigraphic relationship between the layered deposits and boulders therefore suggests that both were probably deposited by the first wave.