重力觀測是用來探索地下構造的優先方法之一。因為它具有方便、快速、低成本的優勢，目前台灣遍布密集的重力觀測點，提供完整的重力觀測資料。本研究分析觀測重力值內包含的訊息，利用g-H關係圖法及Nettleton密度剖面法進行地表岩層密度的估算，其結果能與地質分區對應一致。根據分析結果指出，山區的密度分布約2.4至2.6 g⁄〖cm〗^3 ，西部麓山帶約2.2 g⁄〖cm〗^3 ，西部平原約1.8至2.0 g⁄〖cm〗^3 。經過重力修正得到布蓋異常圖並分析重力效應的波長，將重力效應分為淺層及深層的來源，進行莫荷面的估算及地下密度分布的討論。經訊號分離後的淺層重力效應能與地質分區對應一致；深層的重力效應圖顯示在西部麓山帶下方有一重力低區，推測與地殼增厚有關。我們利用速度－密度經驗轉換公式，將速度構造與重力觀測合併來討論，並分別討論淺層和深層的速度構造與重力效應的異同。透過分析比較，我們可以知道兩者之間仍存在明顯差異。本研究採用二維聯合模擬的方法，彙整TAIGER、ATSEE及TSEE的地震資料及整合後的重力資料進行三條二維剖面的順推計算工作，得到符合走時與重力觀測的二維構造，並加入利用重力資料所求得大尺度的莫荷面深度起伏，可作為未來進行更精細的三維地下構造模擬之初步模型。;Gravity observation is one of priority method that used to explore the subsurface structure. Because it is easy, fast and low-cost, dense gravity observation stations are distributed in whole Taiwan, no exception in mountain area. In this study, the message contained in the observation of gravity values is analyzed. We use g-H relationship and Nettleton′s density determination method to estimate the density of topography. Based on the results, the density value of mountain area ranges from 2.4 to 2.6 g⁄〖cm〗^3 , is 2.2 g⁄〖cm〗^3 in Western Foothills and 1.8 to 2.0 g⁄〖cm〗^3 in Western plains. After gravity correction, we can get Bouguer anomaly value and separate the source of gravity effect to the shallow and deeper part from gravity wavelength. Then, it led to discuss the Moho interface relief and subsurface density distribution. The shallow gravity effect is consistent with the pattern of geological division. The deeper gravity effect map reveals that the gravity low area is existed beneath Western Foothills, it might relate to crustal thickening. We utilized the empirical relations between elastic wavespeeds and density to analysis the consistency between velocity structure and observation gravity. According to analysis and comparison, there are significant differences between the analytical results of two physical properties observations. In this study, we begin from two-dimensional co-simulation modeling method using TAIGER, ATSEE TSEE of seismic data and observation gravity data. Then, the theoretical travel time and gravity value is calculated from three two-dimensional cross-sections across northern, central and southern Taiwan. The results of forward modeling that correspond with travel time and observation gravity and large scale Moho interface relief can be use as better initial model of three-dimensional subsurface modeling.
