Evaluation of tsunami impacts on shallow marine sediments: An example from the tsunami caused by the 2003 Tokachi-oki earthquake, northern Japan
Evaluation of tsunami impacts on shallow marine sediments: An example from the tsunami caused by the 2003 Tokachi-oki earthquake, northern Japan
复制标题
DOI：
10.1016/j.sedgeo.2007.01.010
复制
发表时间：
2007-08-15
影响因子：
2.8
通讯作者：
Okamura, Yukinobu
中科院分区：
文献类型：
--
作者：
Noda, Atsushi;Katayama, Hajime;Okamura, Yukinobu
采用野外地质和数值模拟相结合的方法评价了海啸对陆架沉积物的影响。2003年9月25日发生在日本北方北海道东南部近海的8.0级十胜冲地震引发了局部破坏性海啸。海啸浪的最大爬高达到海拔4米。为了估计海啸对浅海沉积物的影响，我们比较了海啸前和海啸后的海洋沉积物在水深38-112米的粒度，沉积结构，和微体化石含量。在研究区北方部分的内陆架，发现细颗粒减少，特别是细于极细砂，导致平均粒度变粗。有孔虫组合也发生了变化，在粗化的沉积物。另一方面，其他陆架沉积物基本不变或略有细化。我们还模拟了海啸波的速度和方向，以及由建模海啸夹带的粒度。数值模拟结果表明，2003年海啸可以在研究区域的北方部分浅于45-95 m的水深中搬运非常细的沙子。这与海啸过后的实际粒度变化相当。然而，在海啸前的调查之后，一些风暴和潮汐流也可能搅动表层沉积物，因此我们不能得出仅由海啸引起粒度变化的结论。尽管如此，采样和建模相结合的方法是强大的估计海啸的影响下的海。(c)2007 Elsevier B. V.保留所有权利。
A combined approach of field geology and numerical simulation was conducted for evaluating the tsunami impacts on the shelf sediments. The 2003 Tokachi-oki earthquake, M 8.0, that occurred on 25 September 2003 off southeastern Hokkaido, northern Japan, generated a locally destructive tsunami. Maximum run-up height of the tsunami waves reached 4 m above sea level. In order to estimate the tsunami impacts on shallow marine sediments, we compared pre- and post-tsunami marine sediments in water depths of 38-112 m in terms of grain size, sedimentary structure, and microfossil content. Decreases of fine fractions, especially finer than very fine sand, which led to coarsen the mean grain size, were detected in the inner shelf of the northern part of the study area. Foraminiferal assemblages also changed in the coarsened sediments. On the other hand, the other shelf sediments largely unchanged or slightly fined. We also simulated the tsunami wave velocity and direction, and grain size entrained by the modeled tsunami. The numerical simulation resulted in that the 2003 tsunami could transport very fine sand in water depths shallower than 45-95 m at the northern part of the study area. This is comparable with the actual grain-size changes after the tsunami had passed. However, some storms and tidal currents might also be possible to stir the surface sediments after the pre-tsunami survey, so we could not conclude that the grain-size changes had been caused only by the tsunami. Nevertheless, a combined approach of sampling and modeling was powerful for estimating the tsunami impacts under the sea. (c) 2007 Elsevier B.V. All rights reserved.