日本东北地区海啸沉积物的AMS分析的初步报告--18世纪至21世纪
Preliminary Report of the AMS analysis of tsunami deposits in Tohoku -- Japan -- 18th to the 21st Century
摘要：
海啸的沉积记录是评估过去事件发生的宝贵工具，正如大量文献所证明的那样，2004年印度洋海啸和2011年东北海啸之后出现了特别的“繁荣”。尽管有大量的文献，但人们对不断变化的海岸环境在海啸记录中所起的作用了解甚少，对于给定的地点，仍然不清楚最大的海啸是否留下了最大量的沉积物。为了研究这一问题，本研究在日本东北地区的阿贺瓦池塘进行，因为池塘作为一个沉积物捕获器。使用沉积物切片机，1米厚的沉积物被检索，其中4个海啸序列被确定，包括最近的2011年海啸。使用一系列的沉积代用指标：AMS（各向异性的磁化率），粒度分析，石英形态（形态和表面特征）和微体化石的分析，海啸沉积物之间的差异被确定，最重要的是一个明确的变薄的海啸沉积向顶部。根据目前的证据，作者讨论了向上变细是由于至少两个在海啸研究中很少评估的组成部分（1）沉积环境的改变，随着海岸的逐渐人为化，提供了更少的沉积物重新活动;（2）Agawa池塘的逐渐填充，逐渐失去了捕获海啸物质的能力。
英文摘要：
Sedimentary records of tsunamis are a precious tool to assess the occurrence of past events, as attested by an abundant literature, which has seen a particular 'boom' in the aftermath of the 2004 Indian Ocean tsunami and the 2011 Tohoku tsunami. Despite an extensive literature, there is very little to no understanding of the role that the changing coastal environment is playing on the record of a tsunami, and for a given location, it is still unclear whether the largest tsunamis leave the largest amount of deposits. To research this question, the present study took place in Japan, in the Tohoku Region at Agawa-pond, because the pond act as a sediment trap. Using a sediment-slicer, a 1 m thick deposit was retrieved, from which 4 tsunami sequences were identified, including the latest 2011 tsunami. Using a series of sedimentary proxies: the AMS (Anisotropy of Magnetic Susceptibility), grain size analysis, quartz morphoscopy (morphology and surface characteristics) and the analysis of microfossils, disparities between the tsunami deposits were identified and most importantly a clear thinning of the tsunami deposit towards the top. Provided the present evidences, the authors discuss that the upward fining is due to at least two components that are seldom assessed in tsunami research (1) a modification of the depositional environment, with the progressive anthropization of the coast, providing less sediments to remobilize; and (2) a progressive filling of the Agawa pond, which progressively loses its ability to trap tsunami materials.
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