在臺灣的西南海域可以同時觀察到由板塊的隱沒作用以及弧陸碰撞作用形成的增積岩體具有不同的構造型態,因此被認為是研究構造地質的重要區域之一。在過去的研究,前人利用臺灣西南部海域中主要的一條分支斷層作為分界,將增積岩體分成以褶皺逆衝斷層構造型態為主的下部斜坡區,以及高度變形的上部斜坡區。接著從觀察斷層是否出露到海床為判斷依據,將下部斜坡區進一步分成:下部斜坡前緣區(盲斷層為主)以及下部斜坡後緣區(出露至海床的斷層為主)。以上的分區對於構造形貌多屬於大區域性的描述,因此本研究將尺度縮小,著重於觀察下部斜坡區內逆衝斷層以及褶皺的幾何形貌、演化過程、滑脫面和變形前緣的空間分布,並加入南邊馬尼拉隱沒系統的剖面進行綜合性討論。 本研究利用TAICRUST及TAIGER計畫中收集的長支距反射震測資料在ECHOS軟體進行處理與分析,除基本的資料處理流程外,更嘗試以波動方程式(SRME)及Radon濾波器(Radon Filter)的方法降低複反射的干擾,接著再進行疊前深度移位分析(Prestack Depth Migration, PSDM),將原先的時間走時剖面轉換成深度剖面,如此兩個步驟能使震測剖面較深部的構造更清楚呈現,並且對於地層傾角、構造幾何形貌的描述能得到更精確的資訊。 本研究的地質構造解釋以薄皮構造理論為基礎,並且以斷層彎曲褶皺、斷層延展褶皺、基底滑離褶皺三種類型作為模型依據進行討論,結果顯示增積岩體的下部斜坡前緣區以基底滑離褶皺為主(脆性-延性地層);下部斜坡後緣區以斷層延展褶皺為主(脆性地層)。在南邊的馬尼拉隱沒區,只出現斷層延展褶皺;然而在北緯21度以北,開始出現的基底滑離褶皺構造,可以被視為增積岩體在初期弧陸碰撞帶南端的證據之一。
The accretionary wedge offshore southwestern Taiwan is regarded as an important area to tectonic geology studies. Different structural styles formed by the subduction and arc-continent collision processes can be found in the accretionary wedge. In the past studies, the accretionary wedge has been divided into the lower slope with fold-and-thrust structures and the upper slope with highly deformed structures. Furthermore, the lower slope of the accretionary wedge can be separated into two segments: the frontal segment with blind thrusts and monoclines and the rear segment with outcropping thrusts and symmetrical anticlines. While the distribution of the structures are described well in the larger area, our study aim to observe the geometry of the folds and thrusts in a smaller scale, the evolution of the structures and the distribution of the decollement and the deformation front. In this study, we reprocess and analyze several large-offset multi-channel seismic reflection data collecting by TAICRUST and TAIGER plans in ECHOS software. In addition to the basic seismic data processing, we use SRME and Radon filter to reduce the multiples. Finally we do the prestack depth migration converting time domain into depth domain to get better image in the deeper part of the seismic profile and more accurate information about the angle and geometries of the structures. Based on the thin-skin tectonics and the fault-bend folding, fault-propagation folding and detachment folding models, we find that detachment folds (brittle to ductile stratum) are recognized in the frontal segment while the fault-propagation folds (brittle stratum) are dominant in the rear segment. However, only fault-propagation folds are found in Manila subduction zone while detachment folds can be seen as the evidence of the arc-continent collision in the north of 21°N.
為了持續優化網站功能與使用者體驗,本網站將Cookies分析技術用於網站營運、分析和個人化服務之目的。
若您繼續瀏覽本網站,即表示您同意本網站使用Cookies。