台灣為歐亞板塊和菲律賓海板塊的聚合帶，有兩個隱沒系統，東北邊為菲律賓海板塊俯衝隱沒至歐亞板塊下方；而台灣南邊歐亞板塊向東隱沒至菲律賓海板塊。在活躍的板塊構造活動下，台灣的地震頻率高且分布特性相當複雜，對於南台灣的隱沒帶弧前區域至今尚缺乏詳細的構造研究。因此本研究是利用中央氣象局2012-2020年規模大於三的地震資料，研究範圍為在台灣本島和蘭嶼、綠島間的弧前區域，使用鄰近研究區域的19個氣象局測站，藉由這些地震資料反演出一維速度模型。希望透過速度模型結果，結合前人文獻的岩石試驗解釋震波速度與不同岩石的關係，對於南臺灣區域隱沒帶弧前地區的速度構造有更深入的解釋。本研究結果中，反演出的速度與前人研究的速度剖面結果有相互解釋，綜合地震分布狀況，推測在此弧前區域的莫荷面約為17-25公里深。此外，在前人研究的重力模型計算結果中，觀察到弧前區域下方有蛇紋岩化區塊，而本研究的速度模型深度35-70公里有觀察到低速層，推估為蛇紋岩化的地函物質，透過岩性資料比對約有10-15 %的蛇紋岩化程度，從地震分布推估此蛇紋岩化物質對應到弧前下方地函楔的區域。;Taiwan is the convergent boundary between the Eurasian Plate and the Philippine Sea Plate, which involves two subduction systems. In the northeast of Taiwan, the Philippine Sea Plate subducts underneath the Eurasian Plate at the Ryukyu trench, while the Eurasian Plate subducts eastward under the Philippine Sea Plate in southern Taiwan. This active tectonic setting leads to the frequent occurrence and the complicated distribution pattern of earthquakes in Taiwan. Hence, there is still a lack of detailed structural studies of the subduction forearc in the south of Taiwan. In this thesis, we generate a 1D velocity model in offshore southeast Taiwan by inverting the seismic data with a magnitude larger than three from Central Weather Bureau (CWB). Moreover, we combine our velocity model with the laboratory measurements of previous studies to interpret the relationship between seismic velocity and rock types. The result of our study shows the petrophysical analysis of the 1D velocity model layer by layer. The Moho is about 17-25 km deep in this forearc area. Also, a low-velocity layer is observed at a depth of 35-70 km which indicates that the serpentinization of the forearc mantle. After comparing with the rock types, we infer the degree of the serpentinization is about 10-15%. In conclusion, our study provided more details beneath the northern Luzon forearc in southeastern Taiwan.
