枋寮外海海床的地形地貌研究

Geomorphologic study offshore the Fangliao area

10.6342/NTU.2011.03385

邱子軒

潮州斷層 ； 枋寮峽谷 ； 多音束測深 ； 側掃聲納 ； Chaochou fault ； Fangliao canyon ； multibeam ； side-scan sonar

臺灣大學海洋研究所學位論文

2011年

碩士

宋國士

繁體中文

潮州斷層是台灣南部最重要的構造線之一，幾乎呈南北走向，全長約85公里，一般認為它是條帶有左移性質的逆衝斷層，但許多學者在近期的研究都指出潮州斷層的活動性已逐漸減低，甚至沒有在活動的跡象。直到2006年的恆春地震、2010年的甲仙地震，潮州斷層是否還有在活動的議題才又開始廣泛的被討論。本次研究區域是在潮州斷層出海處到枋寮峽谷谷頭間被沉積物覆蓋的部分，我們知道斷層並不是只會在陸地上生成，但在台灣區域 斷層出海後的延伸地球物理證據資料具很缺乏，本研究就是以枋寮外海的地球物理資料之整理結果，想對潮州斷層的出海延伸狀況做一適當的推論。 我們使用多音束測深機來蒐集水深資料，做出高解析度的地形圖，來做更精準、更細微的地形判斷；還有利用側掃聲納系統來做地貌影像的視察，並結合水下攝影機來對海床影像聲納辨識結果提供直接有力的證據；最後，我們更用了高頻震源的震測系統，將淺層的地層資料做全面性的蒐集。 根據地形資料可以看出兩個明顯的地形特徵，其一是施測區域靠近陸地的地方有發現地形隆起的現象，其二是在峽谷頭附近有看到至少兩條指向陸地的破裂。而側掃聲納影像在地形隆起的區域也發現有大量密度不同的水團造成的反射訊號，在這些地方做水下攝影時，有記錄到海床上存在一些疑似液體上竄的孔洞。透過地層剖面得知，中央隆起區域的地層層面是跟著海床面一同彎曲，而不是水平堆積，另外，彎曲的地層被截斷，存在有許多的不連續面。 結果指出，潮州斷層出海處可能和枋寮峽谷相連，潮州斷層一出海便向西南延伸到枋寮外海的地形隆起區，最後連接到枋寮峽谷。而隆起的現象本研究認為此區域的大地應力沿著潮州斷層會帶有左移的性質，因此在轉彎處產生一系列平行的破碎帶。隆起區域也是因應力擠壓造成，側掃聲納的不同密度反射影像和震測剖面上的束狀黑影，都是地層因擠壓脫水所產生。

Chaochou fault is one of the most important tectonic lines in southern Taiwan, it’s almost north-south direction and about 85 Km. Generally believed that it is a thrust fault with left section strike-slip, but many scholars in recent studies have pointed out that Chaochou fault’s activity has been gradually lowered, even has not the signs of event. Until the 2006 Hengchun earthquake and the 2010 Jiasian earthquake, Chaochou fault began to be widely discussed. This study area is the part be covered by sediments between the location of Chaochou fault out of the land and the head of Fangliao canyon, we all know that the fault will not only build on land, but there have rarely cases to research the situation of the fault into the sea, so the purpose would like to know how the Chaochou fault develops after it gets into the sea, and it is related to the adjacent canyon, Fangliao, or not. In order to do better research, we use multi-beam sonar to collect bathymetric data, trying to make high resolution topographic map, to do more accurate, more subtle terrain judge; And use side scan sonar system to do the inspection of the feature image, combined with underwater camera to make the video to provide more direct evidence; Finally, we used three source of seismic which is different from frequency and penetration to ensure that all forms of stratigraphic information can be comprehensive collection. Base on topographic data, there have two distinct features can be seen, one is the survey area close to land have found that the phenomenon of topographic uplift, and the second is that there have at least two breaks near the head of canyon point to the land. The image of side scan sonar at the uplift region also revealed many special reflected signals caused by different density of water masses, taking underwater camera in the area, there have recorded some hole on the seabed and we suspect that there are the pipes for eruption. Final is the data of seismic, through the stratigraphic section that, on the seabed of the same sediment sources, the density of stratum at the central is large than both side, the hardness is also like that, so the central region has poor penetration, also the place can see some bundles of eruption over the seabed. In addition, the uplift of the strata below the seabed is along with bending, rather than the general level of accumulation of sedimentary environment, if we look closer, we can see the presence of curved strata has many discontinuities, but also the ruptures are from the deep began to develop. We speculate by these clues, Chaochou fault is related with Fangliao canyon, if we do an imaginary line to connect these two structures, the line will pass through the uplift area. When combined with tectonic stress in southwestern Taiwan, it can be as a structure with left stress, and then there will form a positive flower structure on the corner by a compressive stress, a series of parallel rupture produce around there. The bulge region is generated by squeezing, let the strata dehydrated, make the density becomes large, and it’s the reason of the poor penetration. In this way, we can solve all sorts of phenomena and complete a seasonable connection.

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