全球衛星定位系統(GPS)原為美國空軍及海軍位軍事上導航、定位所發展出來的。時至今日，以可應用在測量地殼變形及斷層活動的監測。本研究在苗栗通霄、苑裡、三義及台中大甲區域實施GPS監測。目的為了解鐵砧山背斜地區、斧頭坑斷層及其附近地質構造的地殼變動與地表及地下活動斷層之間的關係。 本研究分兩部份進行，首先搜集中央地質調查所、成功大學自1998到2003年期間鐵砧山地區GPS測量資料及本研究在2004年野外觀測資料，配合國內、外固定站，利用Bernese 4.2版GPS資料處裡軟體，解算出測站基線分量及長度的重複性及歷年的水平速率變化，推估其地表移動速率及應變速率。另一方面利用數值模擬軟體Poly3D及Poly3Dinv推演地下的構造。Poly3D假設岩體為彈性體，在此彈性體中建構一或數個由多邊形元素組成的不連續面。在此不連續面上施予應力使其自然產生錯動，進而推算出地表網格變形量。再利用Poly3Dinv逆推模擬，將地表面的位移量代入而快速求得斷層面的錯動量。經由模擬所得變形量可與GPS測量實際觀測的地表變形量相互比較其差異。 Global Positioning System(GPS) is commonly used in geodetic survey. In this reason, we use GPS geodesy to study crustal deformation and fault`s displacement in Tungshiau、Yuanli、sanyi of MiaoLi and Dajia of TaiChung and to interpret the relationship of crustal deformation of the Tienchenshan anticline and subsurface Futoukeng fault. This study comprise two parts. First, we assemble the field survey GPS data from Central Geological Survey and NCU and continuously recording GPS stations. GPS data is proceeded using Bernese GPS software v.4.2 to obtain repeatable quantity of baseline and annual horizontal slip velocities. Secondly, we use Poly3D and Poly3dinv software to infer the subsurface structure. Poly3D assume that the mass is an elasticity body, which establishes one or more discontinuity planes composed by polygonal elements. We can made displacement by giving stress on these discontinuity planes, proceed to calculate the surface displacement. Then we apply Poly3Dinv to model the fault displacement using surface velocity. An interaction of Comparing modeled displacement with observed GPS data we can better constrain the subsurface geometry of the Futokeng fault.
