蘭嶼海嘯石與1867年基隆海嘯之動力分析;Lanyu Tsunami Boulders and Dynamic Analysis of 1867 Keelung Tsunami

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Title:	蘭嶼海嘯石與1867年基隆海嘯之動力分析;Lanyu Tsunami Boulders and Dynamic Analysis of 1867 Keelung Tsunami
Authors:	李珮瑜;Li,Pei-Yu
Contributors:	水文與海洋科學研究所
Keywords:	蘭嶼;海嘯石;海嘯源逆向追蹤法;海底山崩;流固耦合;移動固體法;1867年基隆海嘯;Lanyu;Tsunami boulders;Tsunami Reverse Tracing Method;Submarine landslide;Fluid-solid coupling;Moving Solid Method;1867 Keelung tsunami event
Date:	2015-07-15
Issue Date:	2015-09-23 10:50:17 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究主要分為兩部分進行討論，其一為海嘯源逆向追蹤法（Tsunami Reverse Tracing Method, TRTM）之理論驗證及探討蘭嶼珊瑚礁石之可能來源；其二為山崩觸發海嘯之三維數值模擬，並應用於1867年基隆海嘯之還原與分析。　　TRTM之理論建立在線性假設下，本文驗證其符合疊加理論（Kramers, 1957）及點源離散理論（Fresnel and Chim, 1816）。Ota et al.（2014）於台灣蘭嶼北端之六個位置發現珊瑚礁石，經放射性定年後，其年齡介於距今200年至6000年間，極有可能為古海嘯事件之證據，其中最年輕之珊瑚礁石被認為可能與1771年八重山地震事件有關。本研究利用TRTM探討蘭嶼珊瑚礁石之可能來源，並使用COMCOT求解線性淺水波方程式，對可能之情境案例進行模擬與分析。　　過去曾以TRTM對1867年基隆海嘯事件進行分析，並進一步使用影響強度分析法（Impact Intensity Analysis, IIA）於近岸處進行補強，結果顯示位於基隆東北方之基隆陸棚為海底山崩之潛在來源之一（李, 2014）。本研究以三維模式SPLASH3D結合移動固體法（Moving Solid Method, MSM）針對海底山崩型海嘯之案例進行數值模擬。根據Watts et al.（2005）將滑落過程中有無形變加以區分為塊體崩落（Slides）以及泥沙崩塌（Slumps）兩種形式。模擬結果顯示影響海嘯初始最大負波之主要因素為塊體初始位置及體積。　　結果顯示蘭嶼珊瑚礁石之可能海嘯源位於綠島南方，且其與1771年八重山地震事件之關聯性較小。而造成1867年基隆海嘯事件之可能山崩情境為沿基隆海谷之設置，於金山沿岸及基隆沿岸皆可觀察到大於6.5 m之波高，與鄭（2013）之研究相符。;In this study, two topics are discussed. The first topic is the theory validation of Tsunami Reverse Tracing Method (TRTM) and the study of the possible sources of the coral boulders in Lanyu. The second topic is the 3-D simulation of landslide generated tsunami and its application to the reconstruction of the 1867 Keelung tsunami event. 　　TRTM is established based on the linear hypothesis, and validated to accord with superposition principle (Kramers, 1957) and Huygens-Fresnel principle (Fresnel and Chim, 1816). Recently, six sites of coral boulders have been founded on Lanyu, Taiwan. According to the radiometric dating results, the ages of the boulders are between ca.6000 years BP and ca.200 years BP. The youngest boulder was suggested to be related to the 1771 Yaeyama earthquake event (Ota et al., 2014). Hence, we implemented the Tsunami Reverse Tracing Method (TRTM) to find the possible tsunami sources and solve the linear shallow water equation by COMCOT (Cornell Multi-grid Coupled Tsunami Model) tsunami model to perform the scenario analysis. 　　In the past, the 1867 Keelung tsunami event was studied by the TRTM, and the Impact Intensity Analysis (IIA) method was employed to quantify the tsunami impact from each discretized computational domain. The result showed that three possible landslide scenarios of the 1867 Keelung tsunami event were triggered in the Mein-Hwa Canyon, Keelung sea valley, and Keelung Shelf (Lee, 2014). In this study, we use a 3D fluid-solid coupling model, SPLASH3D to combine the Moving Solid Method (MSM) to validate and simulate the case of submarine slides. According to Watts et al. (2005), the Submarine Mass Failure (SMF) was categorized into Slides and Slumps. The result indicates that the impact of the initial maximum negative wave is effected by the initial location and volume of the SMF. 　　For the coral boulders of Lanyu, the scenario set up in southern Green Island is agreeable with the site of boulders. It seems unlikely that the boulders are related to the 1771 Yaeyama earthquake event because of the weak signal of the numerical wave gauges. The results show that the possible landslide scenarios of the 1867 Keelung tsunami event occurred along the Keelung sea valley. The wave height higher than 6.5 m in Keelung coastal is observed in this study.
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