在天然氣水合物賦存的海域，甲烷與硫化氫等氣體可能從沉積物深部藉由斷層或其他通道往海床上冒出，天然氣往海床的上衝或噴出經常伴隨地質構造形成各式樣貌如泥貫入體、泥火山或麻坑等，因此瞭解海床地貌聲納影像及海床下淺層沉積物的構造和特徵是了解海床下流體及天然氣水合物形成極重要的研究項目。根據第1年的綜合資料分析結果顯示，永安海脊海床上具有聲波的高反射係數特徵，推測可能與岩層遭到侵蝕裸露或自生碳酸?礁的形成有關。此外，永安線形西側的沈積地層中有廣泛的聲波透明層的震測相出現，而此區也有廣泛的麻坑同時存在，因此，推測此區可能是濁流堆積形成的高孔隙率地層，後來成為甲烷氣體的儲集層，而在此溫壓條件下，事實上可能已經形成天然氣水合物的賦存。而在永安海脊東側也有局部的麻坑存在，雖然沒有明顯的聲波透明層現象，但卻有明顯的泥貫入體上衝構造，意味此區可能也有天然氣水合物的存在。在第2年成果中，我們發現Good Weather Ridge西側的近海床特徵，包括海床地貌特徵與淺部地層構造等，皆發現與天然氣有關的地質構造，例如麻坑、自生碳酸?礁等，磁力資料逆推的結果，也發現有些區域與地化資料底水高甲烷的反應可以相搭配。根據綜合解釋的結果，我們推測在Good Weather Ridge西側的區域，天然氣的移棲可能非常靠近地表，幾處大規模的崩塌區，也可能在溫、壓條件合適下，成為天然氣水合物儲集的地方。根據多音束水深資料處理結果，第2年的作業區內的海底地形架構與第1年相同，是以海底峽谷為主，其中伴隨多處塊體滑移的運動與海底崩塌，然而，區域內的侵蝕與搬運作用非常明顯，因此在峽谷的主要河道上並無崩塌物的堆積。另外，新的水深資料在精確度與解析度上，也大幅超越舊有資料的水準，對於日後地調所或是其他工作團隊在調查與規劃上的應用，能提供非常大的幫助，對於繼續擴充研究用的高解析海底地形圖資也有非常重要的貢獻。海底地電阻的發展方面嚐試建立海底地電阻資料的分析、逆推程序，以深化我們的海洋地球物理技術，並評估日本JAMSTEC之DCR系統來台探測可行性。側掃聲納處理軟體的開發也有重大的進展，尤其在剖面的回置步驟上，利用既有EK500水深資料的比對，成功的提高了影像嵌合的準確度，這部分比使用中套裝軟體處理的結果還要好。為了延續前兩年的成果並進一步瞭解其他台灣西南海域天然氣賦存和可能鑽井的考量，我們提出此第三年計畫書，規劃在台灣西南外海的小琉球以南區域進行底拖聲納系統與多音束水深資料的收集，繼續提供天然氣水合物賦存區內的高解析地質、地貌與海底地形資料，作為將來天然氣水合物研究的重要參考資料。 In gas hydrate resources areas, fluid such as methane or sulfide may come to the sea floor through sediment layers by means of faults or other venting passages. The upward flow of fluid may form distinctive features such as mud diapir, mud volcanoes or pockmarks. Therefore, understanding the morphological characteristics of the sea floor through acoustic images of deposited or structural characteristics of shallow sediment layers is important to study the mechanism of sediment fluid flow and gas hydrate formation. According to the results of first year survey, the area in the east of Yung-An Lineament (YAL) belongs to active accretionary prism. We found wide distribution of carbonate in terms of strong acoustic reflection which suggests large methane gas have interacted with sulfate. In this case, the acoustic penetration is very limited and diffraction phenomenon is clear in sub-bottom profiler data. In contrast, to the west of YAL, the sedimentary layers can be clearly identified. The acoustic blanking can be traced along a layer as thick as 30 m, which suggests that this area is not only a high-porosity sedimentary layer but also reserve potential gas-hydrates. In some places, the possible gas-hydrates (blanking areas) even outcrop to the seafloor. In the west of YAL, there are also pockmarks at the same place as the seismic blanking zones. Based on the side-scan sonar data, we found seafloor features of pockmarks and authigenic carbonate in the west of Good-Weather Ridge (GWR) in second year. The analysis of magnetic data is consistent with the high methane concentration from geochemical data. We infer that in the west of GWR methane could migrate upward near seafloor and the area of several submarine landslide deposits could be good place for forming gas-hydrate if the PT condition is suitable. The multi-beam survey in the northern margin of South China Sea shows features of several canyons and possible submarine landslides as same as showed in first year. In the survey area, the phenomenon of erosion and transportation is quite obvious. The new collected bathymetric data is much better than previous old data in terms of resolution. This data set is very helpful for further multi-discipline gas-hydrate studies in the near future. As for the CSEM (Controlled-Source Electromagnetics), we try to build submarine resistance data analysis and reversion flows in order to deepen our marine geophysical techniques and to assess the Japan JAMSTEC the DCR system to survey in Taiwan. For the development of side-scan sonar data processing software, we have adopted EK500 bathymetry to do the layback of deep-towed data. We have also invited two Japanese scientists to help our work. In order to have a better understanding of gashydrate and the possible drilling sites off SW Taiwan. We propose to collect deep-tow acoustic and magnetic data south of Ryukyu Island off SW Taiwan in the third year. To provide futher high-resolution gas hydrate occurrence zone geology, geomorphology and seabed topography data. These data will provide important references for in-depth study of Taiwan gashydrate project in the future 研究期間：9901 ~ 9912
