台灣位於歐亞大陸板塊與菲律賓海板塊間構造交界上，菲律賓活動帶的北端終點，其花東縱谷與海岸山脈為擠壓呂宋島弧的增生部分和呂宋弧前所形成。花東縱谷是一構造板塊碎屑和火山入侵的複雜集合地區。此外，花東地區附近有明顯正的重力異常分布，並顯示最大布蓋重力異常值。本研究中，我們使用重力正推及逆推的方法在花東縱谷附近的玉里地區來調查地下構造。 為了獲得可信的密度構造，利用布蓋異常值檢測幾個地球物理和地質剖面，將可靠的地質圖、速度構造等參考資料當作控制，建立密度構造。使用Talwani方法來計算二維密度模型的效應，所得出的計算值與觀測值相比對。然後，利用嘗試錯誤法進而修改密度模型，最後獲得與觀測重力值符合的密度構造，進一步解釋地下構造形貌。 經由地下構造模擬，可得知地層與斷層之位置。此外，根據結果顯示在海岸山脈底下莫荷面深度約為10公里，而中央山脈底下上部地殼隆起呈褶皺背斜。總而言之，因菲律賓海板塊向歐亞大陸板塊碰撞之因素，造成布蓋異常分布呈西低東高且有一重力異常高區，以及中央山脈底下有一褶皺背斜構造。 ;Taiwan is located on the tectonic boundary between the Eurasian Plate and the Philippine Sea Plate. The northern terminus of the Philippine Mobile Belt is in Taiwan, where accreted parts of the Luzon Arc and Luzon forearc form the Huatung Longitudinal Valley and the eastern Coastal Range of Taiwan, respectively. The Huatung Longitudinal Valley is a complex collection of tectonic plate fragments and volcanic intrusions. Besides, the distribution of the positive gravity anomalies is in the vicinity of Huatung area and there show the maximum value of the Bouguer gravity in this area. In this study, we use the gravity forward and inversion method to investigate a geological profile in Yuli area of the Huatung Longitudinal Valley. In order to derive the reliable density structure, we examine several geophysical and geological profiles using the Bouguer anomaly value along each profile. In modeling of subsurface density structure, available seismic and well data are used to possibly constrain the geometric and/or densities. The effect of two-dimensional density model is calculated using the Talwani technique. Then, we use tried and error method to modify the model and finally get a reliable density structure that conform with observed gravity data. The locations of strata and faults in this area are obtained by gravity modeling. Moreover, the result shows that the depth of Moho beneath the Coastal Mountain Range is about 10 km and the upper crust was uplift and became anticline beneath the Central Mountain Range. In short, because Philippine Sea plate collision to the Eurasian plate, the distribution of the Bouguer anomaly is increasing eastward from the Central Mountain Range to eastern Taiwan offshore and the highest gravity anomalies in Taiwan, and there are folds beneath the Central Mountain.
