台灣東北海域基隆陸棚地質構造分析;Analysis of the geological structure in the Keelung Shelf, off northeast Taiwan

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Title:	台灣東北海域基隆陸棚地質構造分析;Analysis of the geological structure in the Keelung Shelf, off northeast Taiwan
Authors:	黃琪洛;Huang,Chi-Lo
Contributors:	地球科學學系
Keywords:	台灣東北海域;基隆陸棚;海底山崩;科學漁探儀;多音束水深;底質剖面;側掃聲納影像;多頻道反射震測;Offshore Northeastern Taiwan;Keelung Shelf;Submarine Landslide;Scientific Echo Sounder;Multi-beam Echo Sounder;Sub-Bottom Profiler;Side-Scan Sonar;Multi-Channel Seismic
Date:	2016-06-27
Issue Date:	2016-10-13 13:22:00 (UTC+8)
Publisher:	國立中央大學
Abstract:	台灣東北海域位於沖繩海槽之最西側，屬於琉球隱沒系統中的弧後擴張盆地北緣。海槽內分布許多正斷層、海底火山以及熱液噴泉，顯示南沖繩海槽仍處於張裂活動相當旺盛的階段。台灣北部人口眾多且分布密集，而該區域容易遭受隱沒帶地震、海底山崩與海嘯所引發的災害。為了瞭解台灣東北海域的地質構造與海底山崩之潛勢，本研究收集及分析科學漁探儀、多音束水深、底拖側掃聲納系統與多頻道反射震測資料。研究結果顯示基隆陸棚上有許多東北－西南走向的地形線性構造分布，該走向大致與歐亞板塊與菲律賓海板塊的聚合方向垂直，接近台灣主要山脈走向。在基隆陸棚震測剖面可以觀察到許多正斷層大都可向淺部連接到地形線性構造，顯示此區域正處於拉張的應力狀態，但在震測剖面雙程走時1 ~ 1.5秒，仍可發現擠壓褶皺之構造，推測是早期台灣碰撞造山所遺留的構造，如今因碰撞擠壓已變成弧後盆地拉張，因而呈現構造反轉作用的現象。海床逸氣現象主要發現在龜山島附近與棉花峽谷兩側，這些海床逸氣現象可能與火山活動較為相關，而棉花峽谷兩側的逸氣尺度較大，推測是因為下方有一走向滑移斷層，熱液氣體可以沿該地殼破裂處向上噴出。基隆陸坡之坡度約為5° ~ 15°，而部分峽谷區之坡度可達25° ~ 30°。過去的海底山崩事件多發生於坡度較大的位置，應該與邊坡不穩定有關。整合資料分析後，本研究推測未來可能有四區容易於陸坡發生海底山崩，山崩區的水深約200 ~ 400公尺處。而研究區的海底山崩總面積可達390平方公里，而總崩塌體積可達到18立方公里。 ;Located behind the Ryukyu islands, the offshore area of the northeast Taiwan is subjected to the extension of the Okinawa Trough back-arc basin, Normal faults, submarine volcanoes and gas seeps are distributed in the trough, indicating the south Okinawa Trough is very active. Considering the dense population in northern Taiwan, the coastal area of northern Taiwan is under menace of natural hazards from potential large earthquakes and tsunamis. To better understand the seabed features and the potential submarine landslides off northern Taiwan, we have conducted and analyzed marine geophysical surveys off NE Taiwan. In the Keelung Shelf, the seafloor edifices are generally NE-SW trending. The NE-SW orientation is coherent with the trend of the Taiwan mountain belt and perpendicular to the convergent direction of the Philippine Sea Plate relative to the Eurasian Plate. Observed in the Keelung Shelf, the normal faults are due to the back-arc extension. However, structural folds exist in the deeper strata. We suggest that the folds could be the inherited from the early Taiwan orogeny. Using scientific echo sounder, we have found 18 gas flares near the Turtle Island and 21 gas flares around the Mein-Hua Submarine Canyon. Those flare could be related to the back-arc volcanism. The flares near the Mein-Hua Submarine Canyon could be also related to a strike-slip faulting, facilitating the upward migration of the volcanic gas. The continental slope is general about 5° ~ 10° of the Keelung Shelf; however, some slope could be reach 25° ~ 30° at some internal gullies or canyons. Submarine landslides are located at steeper gradient. We suggest that there are four potential submarine landslide areas located at the continental slope of water depth 200 ~ 400 meters. The total volume of potential submarine landslides could be 18 cubic kilometers.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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