全球隱沒帶的板塊撓曲量模擬和地震活動相關性分析

林子峻(Zi-Jun Lin)

指導教授 ： 林靜怡

國立中央大學/地球科學學院/地球科學系/碩士(2015年)

摘要

海洋板塊岩石圈在隱沒過程中，會因為荷重而產生撓曲，並在隱沒帶外側形成地形上的局部高區，通常被稱為海溝外側隆起帶 (outer-rise)，而板塊撓曲程度 (flexural deflection) 通常跟海洋板塊所受到的應力狀態有關。另一方面，隱沒帶板塊邊界間的應力狀態，不僅與海底地形分佈相關，也會影響到板塊的耦合程度，造成不同程度的地震活動。因此，海溝外側隆起帶的形貌應該可以反應出隱沒帶的產震特性。
在本研究，基於海底地形資料和板塊撓曲方程式，我們模擬各個隱沒帶的板塊撓曲程度，並藉由比較撓曲大小和隱沒帶板塊相關參數來探討各隱沒帶的產震特性。我們的模擬結果顯示出隱沒帶的撓曲程度呈現連續性的變化，並和其他區域性研究數值相近，表示模擬的結果是可信的。而所得到全球隱沒帶的撓曲量約介於100和700公尺間，各個隱沒帶間的撓曲量並無太大的差異，但在弱耦合隱沒帶區域，沿著海溝的板塊撓曲量則有較大的變化。另外，我們發現較大的板塊撓曲量通常發生在海溝系統中間的部分，在其兩端則是板塊撓曲量較小。而由板塊撓曲量和其他板塊參數比較的結果，我們發現強耦合隱沒帶的板塊撓曲量分佈和地震規模5到7的數量似乎有相關性，但和其他板塊參數則無明顯相關。

關鍵字

板塊撓曲 ； 板塊邊界 ； 耦合 ； 地震數目 ； 板塊年紀 ； 隱沒速度

並列摘要

Near oceanic trenches, the lithosphere is bent by plate stresses, including vertical and horizontal load. This bending effect, generally known as plate flexure, causes the formation of the outer rise which is often observed on the bathymetry data. The width of the outer rise is directly related to the flexural rigidity of the lithosphere.
Moreover, the wavelength and amplitude of this flexure can be used to constrain the state of stress. In a coupled subduction zone, the stress is largely accumulated across the plate boundary which should affect the flexural properties of the subducted plate. Thus, the variation of the outer rise in shape may reflect the seismogenic characteristics of the subduction system. In this study, we estimate the flexural parameters of subducted plate based on the available bathymetry data. The values of the flexural deflection (Wb) are between 100 and 700 m. Their average value spreads from 348 to 682 m. The worldwide distribution of Wb shows that relatively larger values occur in the center of the trench system. The standard variation of Wb is generally larger in the weak coupling subduction system than in the strong coupling area.
The comparison of Wb and several parameters of the subduction system shows that the Wb is correlated to the number of earthquakes with magnitude between 5 to 7. Otherwise, no clear correlation was found between Wb and other parameters.

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