龍門山造山帶位於四川盆地西緣，在印度板塊持續向北擠壓歐亞大陸的影響下，青藏高原內部物質往南東方向側向擠出，受到四川盆地的阻擋作用，形成了龍門山推覆造山帶。2008年的汶川地震的同震破裂主要由震央開始沿龍門山前緣往北方發展，主斷裂為北川－映秀斷裂帶；和東南方的江油－灌縣斷裂帶，以及介於兩者之間且走向相異的小魚洞斷裂。根據前人研究顯示小魚洞地區是一阻礙斷層傳遞的塊體，反映西南-東北方向之壓應力，在某種程度上阻礙著斷層傳播的速度和方向。本篇的研究方法是透過野外調查並收集斷層擦痕資料來做斷層力學分析，發現金花－紅白場剖面以及漢旺－清平剖面所觀察到的壓應力方向與小魚洞相同且擁有相同的構造特徵。因此我們認為阻礙斷層傳播的塊體非限於小魚洞地區，故使汶川地震的破裂傳遞受到一次以上嚴重的阻擋，這也可能是造成該次地震地表破裂分布如此複雜的原因。中央主斷裂於北川等以北地區在前人研究中都有發現以正斷層的型態出露，然而正斷層出現在逆斷層系統當中實為不合理，因此有科學家認為是逆斷層至近地表翻轉，而以正斷層的型態破裂至地表，但對於翻轉的過程與機制並無詳細的資料能夠加以解釋。在我們的野外調查當中，於中央主斷裂帶經過的東林寺地區亦有發現正斷層的出現，與龍門山中段北川等以北地區的翻轉現象相同。透過進一步調查，發現斷層的翻轉與褶皺構造和斷層發育過程有關。;Longmenshan is situated in west side of Sichuan basin. During the Himalaya stage, Longmenshan orogenic belt was uplift by substance lateral extrusion to the southeast direction under the Tibetan Plateau, and blocking by the Sichuan Basin. Wenchuan co-seismic ruptures propagated to northward along the center segment of Longmenshan, the major fault is Beichuan-Yingxiu fault, Jiangyou-Guanxian fault and Xiaoyudong fault which is a NW-trending rupture. According to previous studies, Xiaoyudong area is salient; it reflects the compressive stress of southwest to northeast direction. In our field investigation, we measurement and record the fault plane datas, to do mechanics of faulting analysis base on the slickenside data. We found the compressive stress direction of Xiaoyudong is same as Jinhua-Hongbai profile and Hanwang- Qingping profile, also in topographic profile. Thus we consider that the salients not only appear in Xiaoyudong aera and surface rupture had blocking more than once during Wenchuan earthquake, it may be the reason why Wenchuan earthquake rupture so complicated. In center fault, there are some previous studies had found normal fault in Beichuan area, they surmise that the reverse fault turn to normal fault when it close to the surface. In our field investigation the fault with overturn is related to fold structure and fault development.
