| 摘要: | 最近之研究發現，位於南中國海東側之馬尼拉斷層有可能在未來200 年內引發規模9 以上之地震並引發強烈海嘯。對台灣而言，馬尼拉斷層引發之海嘯僅需20 分鐘即抵達台灣。在這僅有的時間內，海嘯預警系統不容易發揮作用。而學界能夠貢獻者，實為詳實可靠之海嘯情境分析。因此在第一年計畫中，將邀集地震、地質、與海嘯界之學者，以及南中國海周邊國家之國際海嘯科學相關學者，共同討論以建構合理之情境分析，再透過精準之海嘯數值模擬，以提供民眾與決策者相關侵台海嘯之訊息，包括各地波高、淹溢範圍等。地震海嘯為侵台海嘯之主因。由於海底地震資料取得困難，因而斷層構造不易精確推求。然而透過海嘯源逆推之方法，可間接計算海床之位移量。傳統逆推法受限於單元海嘯或子海嘯之尺度，因此無法很精確推算海床之垂直位移量。本計畫於第二年將建立微小單元海嘯之理論，以突破此一限制，並逆推2006 屏東地震之海嘯源及2004 南亞海嘯之海嘯源。南中國海海域侵台之海嘯在進入台灣海域之前，會先經過台灣南方複雜之海底地形，並將原本長波的海嘯轉化為具頻散效應之介水波。然而過去所使用之數值模式以無頻散效應之淺水波方程式為主，因此在描述介水波上會有較大誤差。本計畫第三年將發展頻散非線性海嘯模式。以顯式蛙跳法求解淺水波方程式，並發展理論公式將數值所造成之數值消散轉化為物理頻散。此模式之完成將對台灣海嘯研究水準有提昇之作用。The resent research shows that the Manila subduction zone in the South China Sea is possible, within 200 years, to generate strong earthquakes of Mw = 9.0 which will induce devastating tsunamis. The first tsunami wave will attack Taiwan in 20 minutes. Due to the short traveling time, the tsunami warning system will work with very limited function. Therefore, reasonable and comprehensive scenario studies are important in terms of tsunami hazard mitigation. In the first year of this proposed project, we shall collect advice from the fields of earthquake, geology, and tsunami sciences to create scenarios, which are reasonable and close to reality. A well-validated numerical model will be used to provide the information, such as tsunami height and inundation area, for residents and policymakers in Taiwan. Earthquakes are the major mechanism for generating tsunami in Taiwan water region. Because of the difficulty in measuring the undersea earthquakes, the fault structure can not be accurately reconstructed. However, by means of tsunami inverse method, the vertical seafloor displacement can be calculated implicitly. Due to the size of the unit tsunami sources, the traditional inverse method is limited on accuracy. In the second year of this proposed project, we will develop the finite unit tsunami source inverse method to improve the accuracy of calculating the seafloor vertical displacement. The innovated method will be used to calculate the tsunami sources of 2006 Pingtung earthquake doublet and 2004 South Asia tsunami. Because of the complex bathymetry in the south Taiwan water region, the tsunami waves from the South China Sea will deform from long waves to intermediate water waves with dispersion effect. However, the numerical models used to simulate tsunami propagation are usually solving the non-dispersive shallow water equations. Therefore, the models have larger errors in describing the waves with dispersion. In the third year of this project, a dispersive shallow water wave model will be developed. The explicit leap-frog method will be adopted to solve the shallow water equations. The numerical damping will be transferred to mimic the physical dispersion. The model is able to improve the research quality of tsunami hazard mitigation in Taiwan. 研究期間 : 9808 ~ 9907 |
