台灣東北角跨雪山山脈與西部麓山帶兩地質區，由數條東北走向的斷層及褶皺縱貫於其中，延伸至外海的區域已進入造山運動後的垮山階段，從擠壓環境轉變為伸張環境，發育一系列的正斷層。位於東北角的鼻頭及龍洞地區，為兩道東北向凸出的岬角，岩層出露狀況良好，能觀察到一系列由正斷層所組成的地塹及地壘。本研究藉由空拍影像建立三維模型，高解析度正射及立面影像，判釋裂隙分布情形，結合野外地質調查，詳細記錄此區域的構造，瞭解鼻頭及龍洞地區裂隙關係及特徵，並分析正斷層可能的成因。鼻頭及龍洞地區分別有五組(BF1-BF5)及六組(LF1-LF6)裂隙，其中BF1及BF2位態能分別對應於LF4及LF5，此兩對能相互匹配的裂隙組各自形成於相同應力環境。鼻頭南岸出露14條北北西向能追跡約百餘公尺的正斷層，斷距介於0.2公尺至3公尺之間；龍洞南區共可觀察到8條西北西向的正斷層，斷距可達4公尺以上，北區能判釋3條西北向正斷層，此外另有5條近南北向的正斷層零星分布於龍洞地區。鼻頭南岸正斷層走向近乎垂直於外海正斷層，且大致平行於近期兩次沖繩海槽開張方向，受沖繩海槽影響較小，斷層位態與鼻頭向斜軸近乎垂直，推估此區斷層與更新世早期垂直褶皺擠壓方向的側向伸張作用有關。龍洞南區西北西向的正斷層走向與萊萊地區的鹼性玄武岩脈長軸方向相似，這些岩脈紀錄了晚中新世地殼的相對伸張方向，此西北西向正斷層可能於此伸張環境下形成，北區西北向正斷層位態大致垂直於蚊子坑背斜軸，推測與鼻頭南岸正斷層為同時期的產物，零星分布之南北向的正斷層多受制於前述兩組斷層，形成於褶皺作用後期。;Northeastern Taiwan straddles two major geologic provinces, including the the Hsuehshan Range province and the Western Foothills province. Several regional faults and folds trending northeast run through it. The orogenic belt extending to the offshore has been subjected to post-collisional collapse, and a series of normal faults have been developed under such a newly extensional regime. A series of grabens and horsts composed of normal faults can be observed in well-exposed outcrops in Bitou and Longdong areas. In this study, three-dimensional models of rock exposure are established via the PIX4D of a drone mapping & photogrammetry software using the aerial images taken by an unmanned aerial vehicle (UAV), and the distribution of fractures is analyzed by high-resolution orthoimages and facade images. Combining these images with field investigation, the structures in this area are documented in great detail. This study aims to understand the possible cause of normal faults. There are five sets of fractures (BF1-BF5) in Bitou area and six sets of fractures (LF1-LF6) in Longdong area. Among them, the attitude of BF1 and BF2 are comparable to LF4 and LF5, respectively. Each matched fracture sets are likely formed in the same stress state. Fourteen NNW-trending normal faults that can be traced about a hundred meters in the southern shore of Bitou cape, the separation of these faults ranges from 0.2 meters to 3 meters. Eight WNW-trending normal faults can be observed in the southern area of Longdong cape, the separation of the normal faults can exceed 4 meters. In the northern area, three NW-oriented normal faults can be identified. Additionally, there are five sparsely-distributed N-S trending normal faults in the Longdong area. We conclude that the normal faults in southern shore of Bitou area are not affected by the Okinawa Trough rifting because the strike of the faults is roughly parallel to the two recent rifting events. The normal fault attitudes are almost perpendicular to the fold axis of Bitou Syncline, it is inferred that the faults in this area may be related to the stretching perpendicular to the major compression direction during the formation of the fold. The WNW-trending normal faults in Longdong area is similar to the direction of the alkaline basalt dikes in the Lailai area. The dikes have recorded the relative stretching direction of the Miocene crust. It is possible that the WNW-trending normal fault may be caused by this extensional event. The NW-oriented normal fault attitudes are almost perpendicular to the fold axis of Wenzikeng Anticline, It is speculated that these normal faults and the normal faults in the Bitou area are developed in the same period. The N-S trending normal faults restricted in between the previous two fault sets and formed during the late stage of folding.
