大崗山位於岡山鎮東北方約4公里，突出於嘉南平原上，南北長約4公里，東西寬不到2公里。小崗山位於大崗山之南，兩山間有高度約50公尺之低平鞍部，其地質情形大致和大崗山相同。小崗山斷層位於大、小崗山的西側，在地形上有明顯的斷層崖，前人的研究中，推測小崗山斷層為一向東傾斜的逆斷層，並在小崗山及阿蓮間形成斷層線崖，推測為逆斷層，東側為上衝斷塊，可能仍在活動。 本研究使用淺層反射震測法針對小崗山斷層及其附近之構造進行調查。在偵測斷層方面，使用五條長測線垂直橫跨斷層預測之位置，測繪小崗山斷層地下結構形貌。另外在永安港至大、小崗山地區之間，沿東西方向佈設了8條短測線，約2公里一條測線，用以調查此區域的地下構造變化。經配合中洲三號井的比對，得到的地下構造由西向東依序為中洲背斜、關廟向斜和大崗山背斜，並加以討論這些構造之間的相互關係。 本研究獲得以下幾點結論： 1、五條橫過斷層的震測剖面皆出現地層攪動之跡象，位置在斷層崖階附近。本研究推測『小崗山斷層』為大崗山背斜下之泥貫入體向上抬升，造成不同地層之間的錯動所形成的。由攪動處近地表地層之扭曲情況來看，可推測斷層活動大概以蠕動方式發生，且持續至今，留下一崖階。 2、大崗山背斜軸位於大、小崗山山腳西側200公尺處，背斜西翼較陡，出露上部古亭坑層，厚約500公尺。背斜東翼較緩，上覆珊瑚礁石灰岩，其下為上部及下部古亭坑層。 3、根據地層的變化情形，可以推測大崗山背斜主要形成的時間是在二重溪層沈積之前。大崗山背斜在上新世蓬萊運動時形成一不對稱的背斜，並承受泥貫入作用向上拱起，後來的海進時期在背斜較緩的東翼上覆蓋一層珊瑚礁石灰岩，西翼則經大量風化侵蝕後才形成現今半面山的地貌。 4、中洲背斜的拱起，主要是來自於下方的泥貫入作用，形成一對稱的背斜形態。另外，上覆在古亭坑層之上的二重溪層也受到明顯的抬昇，且二重溪層厚度變化不大，表示中洲構造是在二重溪層沈積之後才開始活動的。由此推論中洲背斜的形成是在大崗山背斜之後，屬於典型的泥貫入作用。 5、大崗山背斜及中洲背斜之間存在了關廟向斜，此向斜較為平緩，沈積了厚約1000公尺的六雙層及二重溪層。關廟向斜軸偏向東側，推測原因可能是最早受控於大崗山背斜的抬昇，成為單斜構造，後因中洲背斜出現，才在此二背斜之間形成此類似向斜的構造。 The Hsiaokangshan fault is located along the western border of the Takangshan and Hsiaokangshan mounts in the Kaohsiung area, southern Taiwan. The fault extends approximately in the north-south direction with a length of 9 km. Previous studies indicated that the Hsiaokangshan fault is a thrust fault dipping to the east. This study used the shallow seismic reflection method to detect the Hsiaokangshan fault and its neighboring structures. By using five long-range reflection seismic lines, we are able to examine this fault in detail. The obtained fault images of the seismic profiles are of excellent quality. After carefully comparing the reflection layers on each side, we found that the Hsiaokangshan fault should be a normal fault dipping to the west. In addition to the fault detection, we also used eight short-range seismic lines distributed from the Yung-an port to the Takangshan and Hsiaokangshan area to investigate the background geology structure around the fault. The related structures from west to east are the Chungchou anticline, the Kuanmiao syncline and the Takangshan anticline. The research obtained the following results: 1. The structural layers, as seen on the seismic profiles, were disturbed even very close to the surface. It seems that the Hsiaokangshan fault was formed by the mud diapir lifting below the Takangshan anticline. We suspect that the fault might keep movement even up to now, although it could be very slow. 2. The axis of the Takangshan anticline is located at the position 200 meters west of the border of the Takangshan and Hsiaokangshan mounts. Its western limb is steeper than the eastern limb. The upper Gutingkeng formation is dominant near the surface at the axial area. 3. The Takangshan anticline was formed before the deposition of the Erchungchi formation. It became an unsymmetrical anticline by the tectonic pressure from the east occurring at the Pliocene age and then, or spontaneously, lifted by the mud diapir. The eastern limb was covered by the coral reef or the limestone during the transgression time. The western limb, on the contrary, has been greatly eroded due to its high slope. 4. The Chungchou anticline was formed as a symmetrical anticline by mud diapiric lifting directly from the bottom. It was formed later than the Takangshan anticline. 5. The Kuanmiao syncline is located between the Takangshan and Chungchou anticlines, which has the Liushuang and Erchungchi formations deposited on the top with the thickness of about 1000 meters. It could be a monocline caused by Takangshan anticline’s lifting and then changed to a syncline when the Chungchou anticline appeared on its western side.
