1999年車籠埔斷層錯動所引發之921大地震，造成地表破裂與抬升 ，形成近百公里長之「集集地震斷層」。其中學者們對集集地震斷層過大甲溪後往東發展之破裂，提出許多相關研究與探討。本研究利用三維物理模型實驗，以薄皮逆衝理論為實驗基礎，探討影響集集地震斷層北端向東轉折之地下構造。 本研究共分為兩組實驗，第一組實驗先設計一主弱面，模擬可能之集集地震斷層地下形態，並探討與其他相關地質構造之關係；根據第一組實驗結果，確立可能之地震斷層地下形態後，第二組實驗為設計一次弱面，探討影響斷層破裂往東轉折之因素。將實驗結果比對地質調與地球物理資料，提出合理之集集地震斷層北段的地下構造形貌。 第一組實驗結果顯示，集集地震斷層近乎南-北向之破裂帶(即車籠埔斷層)與集集地震斷層北方之三義斷層，屬於同一個南-北走向，且向東傾斜30度之斷層系統上；第二組實驗結果顯示，集集地震斷層越過大甲溪後，受一近東-西走向之地表構造影響，使地表破裂由南-北向轉往東-西向延展，且受來自東南方之大地動力擠壓，使破裂方向由東-西向再轉往東北方向延展。 The Chelungpu fault activity triggered 921 Chichi Earthquake in 1999, the accompanied nearly 100 km long surface rupture is named as Chichi earthquake fault. Efforts have been endeavored to the study of the eastward extension of the fault after crossing through Tachiahsi northwardly. Based on the thin-skin thrust model, this study performed 3-D physical modeling tests for the purpose of realizing the subsurface geologic structures at the turning region of Chichi earthquake fault. Two groups of model designs have been tested in the study. In the first group models, a main weak plane (MWP) has been properly designed to simulate the pattern of Chichi earthquake fault, tests are meant to find out the faulting characteristics in relation to the nearby geologic structures. In the second group models, a sub-weak plane (SWP) has been considered to justify the eastward turning action of Chichi earthquake fault. By correlating the test results with all the available geological and geophysical data, a possible subsurface geologic structure pattern in presented for the northern portion of Chichi earthquake fault. By judging from the test results, it shows that Chichi earthquake fault and SanI fault may both possibly belong to the same N-S oriented fault thrusting system, which dips 30 degrees to the east. And the turning phenomenon of Chichi earthquake fault at Tachiahsi may possibly guided by a pre-existing E-W oriented weak zone at the place. And besides, further northwestward tectonic compression will tend to change the E-W oriented portion of Chichi earthquake fault to a northeastward extension.