琉球隱沒帶最南段位於臺灣東部外海，為呂宋島弧與琉球海溝交界處，該區域為由隱沒作用過渡至碰撞作用的邊界。前人研究認為由於隱沒板塊以方位角308度方向往歐亞板塊斜向聚合，因此聚合速率可分解成垂直海溝方向及平行海溝方向兩個分量，而導致該區域增積岩體有許多西北-東南走向的走向滑移斷層分布。其中最為著名的是西耶雅瑪斷層帶。而這些走向滑移斷層於臺灣東部近海與陸上構造的關聯性，及與周邊區域的構造關聯過去甚少探討。此外，受碰撞作用影響，本區域也可在呂宋島弧東側觀察到許多背向逆衝(Back thrust)構造，由於過去震測系統受限於震源能量不足，受波器浮纜長度過短(短於1000公尺)等因素，因此對研究區域較深部斷層構造的解析力不足。本研究使用國家實驗研究院臺灣海洋科技研究中心的長支距多頻道反射震測系統，於研究區域蒐集了四條跨越呂宋島弧及琉球隱沒帶的震測測線，與沿測線的高解析度多音束水深資料。本研究綜合分析震測、水深及地震分布以瞭解研究區域的斷層活動性。 資料結果顯示右移的走向滑移斷層西耶雅瑪斷層帶可往花蓮近海延伸至新城海脊，沿斷層面皆可觀察到呈現棕櫚樹狀的正開花狀構造，推測為典型的轉換擠壓走向滑移斷層。另外在跨越琉球隱沒帶的一條測線上可以觀察到滑脫面驟降的震測構造特徵。 ;The Ryukyu Subduction Zone located in the eastern offshore Taiwan, where the Philippine Sea Plate is subducting northwest beneath the Eurasia Plate in a 308? direction. Due to oblique subducting, the stress can partition into two components, one is perpendicular to the trench, and the other one is parallel to the trench. It caused that many strike-slip faults occurring at accretionary prism of Ryukyu subduction zone. The West Yaeyama Fault Zone (WYFZ) is one of major strike-slip faults. However, near shore extension and relationship to on shore structures in particularly to WYFZ is less discussed. In addition, previous studies also reported plenty of back thrusts in the northern Luzon arc collision area. Due to low capacity of MCS surveys in past decade, deep crustal deformation and structures are still blurred. In this study, acquiring four 2.5 km long offset multi-channel seismic profiles by using TORI (Taiwan Ocean Research Institute) seismic system across northern Luzon arc and southern tip of the Ryukyu trench area. By integrated analyses on seismic structures, seafloor morphology and seismicity, a new strike-slip model is proposed in this study. The reflection seismic profiles show that the right-lateral transpressional WYFZ can be extended northwestward to the Hsincheng Ridge. In addition, the seismic profile reveals the seismic feature of D?collement step down.
