Department of Geography, Tokyo Metropolitan University 1-1 Minami-Osawa, Hachioji City, Tokyo, 192-0397, Japan.
Research Centre for Palaeoclimatology, Ritsumeikan University 122-12-1 Torihama, Wakasa-cho, Mikatakaminaka-gun, Fukui Prefecture, 919-1331, Japan.
Sci Rep. 2019 Jul 16;9(1):10251. doi: 10.1038/s41598-019-46584-z.
Information on palaeo-tsunami magnitude is scientifically and socially essential to mitigate tsunami risk. However, estimating palaeo-tsunami parameters (e.g., inundation distance) from sediments is not simple because tsunami deposits reflect complex transport processes. Here, we show a new approach to estimate tsunami inundation distance based on the mixture ratio of gravels from several sources in tsunami deposits. We measured the roundness of source gravels in modern beach and fluvial deposits in a coastal valley in Japan through image analysis and then calculated the mixture ratio of both sediment types in tsunami deposits. Normalising the mixture ratios by inundation distances revealed an abrupt change in the mixture ratio at a constant percentile, regardless of tsunami magnitude. This relation allowed estimation of the inundation distance of palaeo-tsunamis during the last 4000 years.
古海啸规模的信息对于减轻海啸风险在科学和社会方面都是至关重要的。然而，从沉积物中估计古海啸参数（例如，淹没距离）并不简单，因为海啸沉积物反映了复杂的输运过程。在这里，我们展示了一种基于海啸沉积物中来自多个源的砾石混合比来估计海啸淹没距离的新方法。我们通过图像分析测量了日本沿海山谷现代海滩和河流沉积物中源砾石的圆度，然后计算了海啸沉积物中两种沉积物类型的混合比。通过淹没距离对混合比进行归一化，无论海啸规模如何，在一个固定的百分位数处，混合比都会发生突然变化。这种关系使得能够估算过去 4000 年期间古海啸的淹没距离。
