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| 題名: | 台灣鄰近海域由陸延伸之斷層及地體構造研究-以花蓮、宜蘭及竹苗海域為例;Active faults and tectonic structures from onshore to offshore of Taiwan : case studies of Hualien, Ilan, and Hsinchu-Miaoli offshore area |
| 作者: | 林廉凱;Lin, Lien-Kai |
| 貢獻者: | 地球科學學系 |
| 關鍵詞: | 米崙斷層;花蓮海脊;宜蘭海脊;中央山脈;新竹斷層;變形前緣;Milun fault;Hualien Ridge;Ilan Ridge;Central Range;Hsinchu fault;deformation front |
| 日期: | 2024-07-26 |
| 上傳時間: | 2024-10-09 15:38:58 (UTC+8) |
| 出版者: | 國立中央大學 |
| 摘要: | 台灣四面環海又位於板塊交界處，地震相當頻繁，分布著許多活動斷層構造。有些構造分佈甚至連接陸海域，故了解陸-海相連的完整斷層分布與構造相當重要。過去，海域缺乏活動斷層及地層構造的詳細調查，因此本研究使用電火花高解析反射震測搭配多音束水深、側掃聲納影像、底質剖面、傳統空氣鎗反射震測、地震資料，完整地分析陸-海域相連的斷層與構造分布並進行地體構造上的解釋。本研究以縱谷北端花蓮、宜蘭、竹苗為研究區域，主要三項研究結果分述如下。（一）花蓮縱谷北端連接到琉球島弧的區域一向被認為是板塊從碰撞轉換到隱沒之處，此區域最明顯的構造是花蓮海脊。花蓮海脊被一北偏西60度的凹陷地形分隔為南北兩段，南段水深較淺且持續抬升，北段較深且構造已不活躍被厚度達100公尺的沉積物覆蓋，南北高低落差約100公尺。南段出露北偏東30度的線性構造與米崙台地為相連的橫移壓縮斷層系統，推測因板塊碰撞末端所形成，米崙斷層是此斷層系統的最西界，研究推測米崙斷層向海域可延伸到約24度3分的位置，剛好就是北偏西60度地形分野處。（二）宜蘭海脊位於中央山脈順時針旋轉側向脫出與沖繩海槽弧後張裂交互影響的位置，從地形上可以區分為北宜蘭海脊與南宜蘭海脊。研究結果顯示，宜蘭陸棚底下的基盤相連，北宜蘭海脊與雪山山脈為同一褶皺構造，並因為垮山形成北偏東45度的正斷層，N斷層系列。隨著中央山脈西翼基盤側向脫出，南邊的北宜蘭海脊這側開始受到影響轉變為北偏東60度走向的正斷層，M斷層系列，並一路延伸到外側遺留下來的褶皺構造，地形上是北偏東60度到75度走向構造脊。隨著中央山脈西翼側向脫出的結束，開始往南宜蘭海脊方向垮塌。南宜蘭海脊是中央山脈東翼延伸，與中央山脈西翼間形成一左移斷層。中央山脈東翼的旋轉脫出形成往北傾正斷層，並可能延伸自南宜蘭構造，與北宜蘭海脊褶皺垮塌的往南傾正斷層，形成了約北偏西60度走向的正斷層帶，S斷層系列。底質剖面與水準觀測結果顯示，M斷層系列及其延伸的濁水斷層與蘭陽溪口，是現今宜蘭海域斷層最活躍以及宜蘭平原下陷量最大的地方。換言之，宜蘭平原現今的拉張主要是來自中央山脈基盤側向脫出的影響。（三）新竹-苗栗區域在造山運動開始後，原先往西北方向移動的低角度逆斷層，在第三紀前的正斷層面開始反轉成高角度逆斷層。最主要的構造以斷層擴展褶皺為主，前緣有高角度逆斷層，走向以東-西向為主，總共分辨出三套不同的褶皺與斷層系統。由北到南，湖口外海的Fold I褶皺與新竹外海的Fold II褶皺，以及對應到的F1與F2斷層系列之走向以北偏東70度為主。F1a及F1b斷層是由北往南的斷層擴展褶皺可能與由北往南逆衝的湖口斷層構成一個橫移壓縮的右移斷層系統，或是與鳳山溪走滑斷層構造相連並截切了湖口斷層。F2a斷層則與新竹斷層為同一斷層系統，Fold II與青草湖背斜為一連續褶皺。苗栗外海的Fold III褶皺與湖口及新竹外海看到的有所不同，走向變成是以北偏東45度為主且被東西走向的斷層截切。F3a斷層根據位置和走向可能與龍港斷層相連。本研究將變形前緣位置的最西邊劃在大約東經120度26分，到了南邊的苗栗外海開始往回在台中接回陸地，往北則是沿著湖口外海的Fold I前緣到桃園接回陸地。;Taiwan island is located at the junction area of Eurasian Plate and Phillippine Sea Plate. Numerous active faults are distributed all over the Taiwan; some are even extend into the offshore area. Therefore, to understand a complete fault distribution and structural morphology, it is crucial to study both the onshore and the offshore area of the structure. There was a lack of data to study detailed active faults and geological structures in the offshore area. Hence, in this study we used sparker high-resolution reflection seismic, the multibeam bathymetry, sidescan sonar image, sob-bottom profiler, air-gun reflection seismic, and earthquake data, to analyze the distribution of faults and structures in the offshore area and provide tectonic interpretations. The offshore areas of the Hualien, Yilan, and Hisnchu-Miaoli are used as three case studies, as follows. (1) The junction area between northern end of the Longitudinal Valley and the Ryukyu Arc system is the transition from plate collision to plate subduction. Hualien Ridge is one of the obvious features in between. Tectonically it is divided into the active southern part and the inactive northern part. In the southern Hualien Ridge, we find several ~N30◦E trending active faults and some could be linked to the active faults in the onshore Milun Tableland. The structures in the southern Hualien Ridge and the Milun Tableland display a pop-up structure that is subject to the oblique compression from the northwestward motion of the Philippine Sea Plate. The ~N30◦E trending faults are the results of the transpressional system. The Milun Fault is the western boundary of the fault system, which probably terminates northward near 24◦03’N where a pronounced bathymetric depression trending N60◦ W. (2) Yilan Ridge situated at the transition between the Central Range extrusion and Okinawa Trough back-arc basin. Physically it is divided in to the Northern Yilan Range (NYR) and Southern Yilan Ridge (SYR). Based on the seismic profiles, the NYR fold may connect to the Hsuehshan Range. Due to the mountain collapse in NE Taiwan, the N fault series were found on the basement offsets and trending about N45◦E extends to the northern Yilan plain. Nevertheless, the extension between the western flank of the Central Range clockwise lateral extrusion and the NYR Fold, changed a normal fault series trending primarily N60◦E on the NYR Fold, named M fault series. M fault series have propagated eastward along the NYR Fold till the end of the western flank of the Central Range, then connected to the remnant folding structural ridge about N60◦E to N75◦E trending and collapsed to the SYR. The eastern flank of the Central Range extends to the SYR and formed a left-lateral strike-slip fault between the eastern and western flank of the Central Range basement. Because the eastern flank of the Central Range basement is undergoing the clockwise lateral extrusion, and formed the north-dipping normal faults. The north-dipping normal faults extended from the Central Range (Southern Ilan Strcture) and the south-dipping normal faults collapsed from the NYR Fold are a N60◦W fault zone in SYR, called S fault series. Based on the sub-bottom profiles and leveling observations, the most active M fault series in the offshore area could extend to the most active subsidence area in the Ilan plain where is the Choshui Fault and the estuaries of Lanyang River. In other words, the extension of the Ilan plain are due to the Central Range lateral extrusion. (3) In the Hsinchu-Miaoli area, the pre-Tertiary normal faults reactivated after the mountain building, and forming the fault-propagation folds. The trending of the Fold I in Hukoo offshore and Fold II in Hsinchu offshore are N70◦E. Faults F1b and F1a are the transpressional faults with a fault-propagation folds thrust from the north. This could be linked to the Hukou fault directly from the offshore to the onshore, or to the Fengshan river strike-slip structure and cut the Hukou Fault. Fold II and the onshore Chingtsaohu anticline onshore are the continuring folds, and Fault F2a may link to the Hsinchu fault as the same fault series. Fold III in Maioli offshore is really different from the Fold I and Fold II. The trending is N45◦E, and cut by the F3 fault series in W-E trending. Fault F3a is possibly linked to the onshore Longkang Fault. The deformation front is defined as the location where strata has been deformed compressional. The new deformation front has extended to the offshore area from Taichung in the northwest direction and reaches the westernmost at about 120。26’E , finally the trace of the deformation front connects back to the onshore Hukou Fault, foothills in Taoyuan. |
| 顯示於類別: | [地球物理研究所] 博碩士論文
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