本研究利用2010年7月、2011年1月~2018年12月中央氣象局的連續地震站，以及中央大學的臨時地震站的觀測資料，探討中央山脈南段的地震活動。參考由Huang等人(2014)提出之三維速度模型，再利用雙差分層析法(Double difference tomography)做反演算得到研究區域內的地下速度構造。由P波速度剖面得知歐亞板塊與菲律賓海板塊的地殼厚度不同，且兩個板塊交界處位在花東縱谷下方；在約30公里深處，海岸山脈下方之P波速度較快，中央山脈下方之P波速度則較慢，顯示菲律賓海板塊與歐亞板塊之P波速度不同。由Vp/Vs比值發現，在花東縱谷下方傾角向西至中央山脈下方有一個比值低區，可能與黑色片岩存在有關。透過速度—密度轉換式，將反演算之速度構造轉換至密度，計算布蓋異常值趨勢與觀測布蓋異常值相似度不高。由於深度約5~10公里的淺層低速區，導致中央山脈有一個重力低區。;This study uses data obtained from Central Weather Bureau’s and National Central University’s temporary seismic stations between July, 2010 and January, 2011 to December, 2018, to detect the seismic activity in the southern Central Range. In this study, we use the three dimensional velocity model that proposed by Huang et al. (2014) as initial model to obtain the velocity structure in the research area with inversion. From P-wave velocity profiles, we find that the crust thickness between Eurasian Plate and Philippine Sea Plate are different. The boundary between these two plates is under the Longitudinal Valley. The P-wave velocity beneath the Coastal Range is faster than the Central range about 30 kilometers deep, and it shows that the geophysics properties between Eurasian Plate and Philippine Sea Plate are different. There is a low Vp/Vs ratio zone beneath the Longitudinal Valley, which may be caused by black schist. With the equation to convert velocity to density, we convert the inversion velocity structure to simulate the density structure. The trend in calculated Bouguer anomaly is not similar to the observed Bouguer anomaly. We find a gravity low in Central Range, it may be caused by the effect of low velocity zone 5~10 kilometers deep.
