Preservation potential of 2004 Indian ocean Tsunami sediment in low-lying areas, Changwat Phuket

After the 2004 Indian Ocean tsunami event, studies on tsunami deposit has increased. Preservation potential of tsunami sediment, which is evaluated from their sedimentary structures and thickness (Szczucinski, 2012), is of the utmost importance for estimation of recurrence intervals of tsunamigenic earthquakes. A low preservation of tsunami deposits in the geological record may lead to an underestimation of tsunami hazard (Spiske, 2013). Phuket was one of the areas most affected by the 2004 tsunami event. Although tourism is developed in the coastal areas and may disturb the tsunami deposit and its preservation, we found a 3 to 20 cm layer of sand which was interpreted as 2004 tsunami deposit in Layan Lagoon and Laguna area. These sand layers consist of fine to coarse sand, normal grading, mud rip-up clasts, sharp basal contact and few shell fragments. The 2004 tsunami deposit is underlain and overlain by fine-grained sediments commonly deposited by suspension in the lagoon which lead to high preservation potential of tsunami sand layer. In contrast, the low potential area is represented by the Bangtao area. The preservation potential depends on depositional environment (e.g. lagoon or plain), climate (e.g. arid or tropical) and anthropogenic modification such as land development for tourism or tin-mining. It is found that the sedimentation rate in Layan Lagoon and Laguna area are 2.2 cm/yr and 2.5 cm/yr, respectively.2004年印度洋海啸事件发生后，有关海啸沉积的研究数量显著增长。海啸沉积物的保存潜力可通过其沉积构造与厚度进行评估（Szczucinski, 2012），该指标对于致海啸地震的复发间隔估算至关重要。地质记录中海啸沉积物的保存程度偏低，可能会导致海啸灾害风险被低估（Spiske, 2013）。普吉岛是2004年海啸受灾最严重的区域之一，尽管沿岸旅游业发达，可能会扰动海啸沉积物及其保存环境，但研究团队在拉扬泻湖（Layan Lagoon）与拉古那（Laguna）区域发现了一层厚度为3至20厘米的砂层，经解释为2004年海啸沉积。该砂层由细至粗粒砂组成，发育正粒序构造、泥质撕裂屑、清晰的基底接触界面，并含少量贝壳碎片。2004年海啸沉积的上下覆层均为泻湖环境下悬浮沉积形成的细粒沉积物，这使得该海啸砂层具备较高的保存潜力。与之形成对比的是，邦涛（Bangtao）区域属于低保存潜力区域。沉积物的保存潜力主要受沉积环境（如泻湖或平原）、气候（如干旱或热带气候）以及人为改造活动（如旅游业开发或锡矿开采）的影响。经测定，拉扬泻湖与拉古那区域的沉积速率分别为2.2厘米/年与2.5厘米/年。