馬尼拉海溝為台灣與菲律賓間最為活躍的板塊邊界，北起台灣西南外海，南至菲律賓民多洛島西北外海，南北兩端皆因弧陸碰撞而終止。根據三維地體動力模擬海洋與大陸板塊同時隱沒的結果，大陸岩石圈的隱沒碰撞會在平行海溝的方向撕裂上部地函中的隱沒板塊，接著在海洋與大陸隱沒板塊的側向交接處產生垂直海溝方向的斷裂，形成平行海溝的軟流圈流場。剪力波在非均向性介質傳遞會產生分離。礦物晶格的因應力形成特定排列方向所產生的非均向性是地函中非均向性的主要來源，上部地函中常見的非均向性礦物為橄欖石及輝石，其對稱軸呈優選排列方向，可反映出板塊絕對運動方向或是地函流場的方向。本研究以民都洛島為主要研究範圍，從2013年起陸續佈置了五個寬頻地震測站，紀錄2014至現今的地震資料。我們藉由剪力波經過非均向性構造會分離出快波以及慢波的特性，分析寬頻站所收集到的遠震波相(teleseismic events)，如SKS以及SKKS，求得快軸方向以及快慢波到時差，來探究民都洛島西北地區上部地函的非均向特性以及分佈範圍。 ;The Manila Trench, stretched from offshore SW Taiwan to the north to offshore NW Mindoro to the south, is the most active plate boundary between Taiwan and the Philippines. Both ends of the Manila Trench are terminated by arc-continental collision. According to 3D numerical simulations of coeval subduction of oceanic and continental lithospheres, the continental subduction/collision would induce trench-parallel slab tearing in the upper mantle, followed by trench-normal tearing near the continent-ocean boundary and toroidal asthenospheric flow. Shear wave splits propagating through anisotropic medium. Stained-induced certain arrangements of mineral crystals called lattice preferred orientations (LPO), which is the main source of anisotropy in the mantle. Olivine and pyroxene are abundant anisotropic minerals in the upper mantle, whose LPO generally reflects the direction of absolute plate motions or mantle flow. In this study, we investigate the upper mantle anisotropy beneath NW Mindoro using data of teleseismic SKS and SKKS as recorded by five broadband stations deployed since 2014 therein. Resulting patterns of fast directions and delayed times will help mantle flows induced by continental subduction.
