台灣中部地質構造複雜，涵蓋褶皺、多條斷層、構造盆地、高山變質帶等構造單元，反映了中央山脈與西部麓山帶之地體演化及地下物性分布之差異。為探討台灣中部地下構造，本研究針對台灣中部地區進行0至50公里深度範圍、0.05°網格的三維速度構造建模以探討地殼變化，將地震與重力資料進行順序反演(Sequential Inversion)分別得到速度與密度模型，首先藉由雙差分層析成像法(tomoDD)得一速度模型，再使用經驗公式(Brocher, 2005)將速度轉換為密度模型，將重力資料加入以進行重力反演，即完成一次順序反演，共計三次反演流程。淺層深度段因地震波線交集過少導致解析較不足，重力資料的整合有效補償了淺層（7公里以上）解析範圍的限制，並使模型更靠近重力觀測的結果。台中盆地沉積層厚度可達約5公里，埔里盆地基盤以上沉積物厚度應小於2公里。西部平原之廣大重力低區為沉積物以及下方整體地殼增厚之綜合效應。地利與梨山斷層下方的密集地震分布與高Vp/Vs比值的垂直構造，應與速度構造中所呈現的滑脫面有關，並顯示地利斷層以東20公里範圍內為主要擠壓變形帶。在中央山脈下方約15至25公里深處，觀察到一與山脈走向平行、約10公里厚的低速構造，自埔里盆地起向南延伸，滑脫面的位置與廬山層的岩性特徵高度吻合，可能和造山作用有關。

The geological structure of central Taiwan is complex, comprising various structural units such as folds, multiple faults, structural basins, and high-grade metamorphic belts. These features reflect the differences in tectonic evolution and subsurface physical properties beneath the Central Range and the Western Foothills. To investigate the subsurface structure of central Taiwan, this study constructs a three-dimensional velocity model with a spatial resolution of 0.05° and a depth range from 0 to 50 km to explore crustal variations. A sequential inversion approach was applied. First, a seismic velocity model was derived using the double-difference tomography method (tomoDD). This velocity model was then converted into a density model using an empirical relationship (Brocher, 2005), followed by gravity inversion using observed gravity data. Each cycle of these steps constitutes one sequential inversion, and a total of three inversion iterations were performed. Due to limited ray coverage, the shallow part of the model (above 7 km) has relatively low resolution. However, the integration of gravity data effectively compensates for this limitation and improves the model's consistency with observed gravity anomalies. The sedimentary thickness in the Taichung Basin is estimated to reach approximately 5 km, while that above the basement in the Puli Basin is likely less than 2 km. The extensive gravity low observed across the western plain results from a combined effect of sedimentary accumulation and underlying crustal thickening. A concentrated distribution of earthquakes and a vertically extensive zone of high Vp/Vs ratios beneath the Dili and Lishan faults are interpreted to be related to a décollement structure identified in the velocity model, indicating that the area approximately 20 km east of the Dili Fault is a major zone of compressional deformation. Furthermore, beneath the Central Range, a low-velocity structure approximately 10 km thick and located at depths of 15–25 km is observed to extend southward from the Puli Basin, parallel to the mountain belt. This structure corresponds spatially and lithologically to the Lushan Formation and is likely associated with the active orogenic processes.

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