馬尼拉海溝地震引發海嘯的潛勢分析

Analysis of the Potential Tsunami Generated by the Earthquakes along the Manila Sub-duction Zone

黃惠絹(Huei-Jyuan Huang)

指導教授 ： 吳祚任 ； 蔡武廷 ； 陳伯飛

國立中央大學/地球科學學院/水文與海洋科學研究所/碩士(2008年)

摘要

根據歷史海嘯資料，大部分的海嘯事件皆由海底地震引發，且其中較具威脅性者多由隱沒帶上的海底地震所引起，因此，本研究以位於台灣西南方的馬尼拉海溝為研究區域，探討馬尼拉海溝地震引發海嘯的潛勢分析
。本研究分成兩個方向分析馬尼拉海溝的地震參數，第一個部份根據Kirby (2006)，將馬尼拉海溝分成六個區域，每一個區域包含一個假設的破裂面，並且考慮馬尼拉海溝分布曲率建立馬尼拉破裂面七與破裂面八，最後利用Papazachos et al.(2004)提供的迴歸式，計算出每一個破裂面的寬度與平均滑移量。第二個部份將六個破裂面的長度相加，建立一個全長990公里的馬尼拉破裂面，並且利用過去百年來的三大地震推算破裂面參數。最後將參數代入斷層模式中計算地表變形造成的海水面變動，再經由海嘯數值模式模擬海嘯波的傳播情形。
經由模擬結果指出，當波高由發震地點傳播至南中國海時，波高已明顯減少，然而，當海嘯波經過中國東南外海的大陸斜坡與大陸棚後，海嘯波高反增加60%。而當全長990公里的馬尼拉海溝破裂時，海嘯波在台灣南部地區以及宜蘭蘇澳一帶將引起約5公尺的波高，在中國東南地區以及越南地區引起10公尺以上的波高，而呂宋島地區為距離震央最近的島嶼，故海嘯波在呂宋島地區引起將近15公尺的波高。除了呂宋本島僅有10分鐘與台灣南部僅有20分鐘時間讓沿岸居民進行疏散，其他環南海諸國地區都有充分的時間進行撤離。
除此之外，本研究比較全長990公里的馬尼拉破裂面之模擬結果與2004年蘇門達臘海嘯事件的異同。以蘇門達臘海嘯事件而言，其海嘯由發震地點至斯里蘭卡、印度的距離與本研究假設全長990公里的馬尼拉破裂面的位置至越南的距離相同，兩者造成的海嘯波抵達時間與波高都很相近。不同的是，南中國海地區海域面積與印度洋海域面積相差200倍之多，因此，當印度洋發生海嘯事件時，海嘯能量將不斷往廣闊的深海地區傳遞，然而當南中國海發生海嘯事件時，海嘯能量將集中在封閉且狹小的南中國海海盆中，故對環南中國海沿岸地區的影響將更甚於環印度洋沿岸地區。
以上研究結果中說明南中國海海嘯預警系統的必要性，雖然全長990公里的馬尼拉破裂面錯動的機率並不高，一旦發生，南中國海環海諸國都將受到海嘯波嚴重的破壞。

關鍵字

馬尼拉海溝 ； 海嘯 ； COMCOT

並列摘要

Almost all devastating tsunamis were triggered by shallow earthquakes in sub-duction zones. We thus focus on the Manila sub-duction zone (or called Manila Trench), deemed as the most likely source region within the South China Sea (SCS), to assess the potential tsunami hazards in Taiwan.
To cope with the changing strikes, we group the entire Manila Trench into six hypothetical fault segments, similar to those of Kirby (2006). The width and dislocation of each fault are then inferred from its length, according to the empirical relations of Papazachos et al. (2004). In addition, by summing all the six fault segments, we create a hypothetical 990 km long fault along the Manila Trench, whose width, dislocation and focal depth are determined based on the data of the three largest earthquakes occurred in the past one hundred year .
Upon simulation of tsunami caused by earthquakes on hypothetical faults, results indicate that the heights of tsunami waves decreases as they propagate from the source region into South China Sea (SCS). However, a 60% amplification of wave height is observed along the southeast China offshore when the wave crossing the continental slope and shelf. For the 990 km long fault scenario, the tsunami wave height reaches about 5 m in southern Taiwan, Suao, and Ilan. It reaches about 10 m in southeast China and Vietnam. For the island nearest to the source region, Luzon island, the tsunami wave height can reach as high as 15 m. Simulation results of the worse case scenario also indicate that tsunami waves will arrive at the Luzon island 10 min after the earthquake and the southern Taiwan 20 min after. The more than 20min evacuation time for other regions suggests that the establishment of an effective tsunamis warning system is plausible.
We also compare the simulation results of the 990 km long fault with the tsunami of the 2004 Sumatra earthquake. The epicenter distances from Sumatra to Sri Lanka and India are comparable to those from Manila to Vietnam. As the results, we deduce comparable tsunami arrival times and wave heights along Sri Lanka, India, and Vietnam. However, while the tsunami waves can propagate further into the open Indian Ocean for the Sumatra case, the relative closeness of SCS tends to trap tsunami waves, causing more damages for Manila case.
Manila results of this study suggest that the establishment of SCS tsunami warning system is worthwhile and earthquakes in Manila sub-duction zone need to put into highly alert.

並列關鍵字

COMCOT ； tsunami ； Manila trench

參考文獻

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