台灣西南部滾水坪的構造活動性和泥火山機制;Tectonic activity and mud volcanism at Gunshuiping, Southwestern Taiwan

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Title:	台灣西南部滾水坪的構造活動性和泥火山機制;Tectonic activity and mud volcanism at Gunshuiping, Southwestern Taiwan
Authors:	阮國桃;Nguyen, Ngoc-Thao
Contributors:	應用地質研究所
Keywords:	活動構造;斷層滑移速率;古亭坑層;全新世;泥火山;Active tectonics;fault slip rates;mud volcanoes;Gutingkeng formation;Holocene
Date:	2023-02-02
Issue Date:	2024-09-19 17:25:16 (UTC+8)
Publisher:	國立中央大學
Abstract:	泥火山常見於世界各地的聚合構造中，在台灣南部沿岸平原及西部麓山帶的斷層軸線或背斜軸軸部亦常發現泥火山的蹤跡，且主要以晚中新世至更新世的古亭坑層泥岩為主，厚度約3-5公里。下部古亭坑層泥岩為鬆軟的沉積岩層且富含過壓流體，可解釋活動泥火山出現的原因。InSAR(合成孔徑雷達干涉)和GPS(全球定位系統)觀測結果表明全新世沿海平原存在著一條西南走向的右移斷層，因此我們推斷其斷層跡應與地形崖和滾水坪穹頂狀泥火山（高雄鹽巢區）的位置有關。現今穹頂狀的地貌被地形崖切穿向右錯移，可能與斷層活動有關。此外，泥火山的噴泥口均座落於東南側且沿斷層跡方向，此現象促使我們研究導向於探討活動斷層的運動學機制以及斷層與泥火山形成的關係。本研究考慮了兩種可能形成泥火山的機制：泥漿通過斷層或裂隙向上遷移，或者透過韌性“貫入”的方式。我們將利用 19 個淺井的鑽探資料、放射性碳定年法 (14C) 、鈾釷 (U-Th) 定年法和地電阻影像剖面法 (RIP) 去調查全新世地層的變形情況，並沿推測的斷層跡的兩側岩層做地層對比。於垂直斷層的剖面結果顯示東南側基岩層沿斷層被抬升，其斷面傾向東南70度，且全新世上部地層亦沿斷層發生變形。同時，平行斷層剖面顯示被掩埋的4,700年地層呈近水平分佈，與穹頂狀地貌形成明顯對比，意謂著該地形最早始於4,700年。由岩心紀錄觀察到4,700年的岩層為泥漿侵入的海相沉積物。此外，在此岩層以上的地層岩性為含泥流的粉砂質黏土層，此岩層底部的定年結果為4100年。因此，我們提出形成穹頂狀地貌的主因是泥漿經由裂隙或斷層流經年代4700年的岩層遷移至地表並在地表流動的結果。再者，由沉積物從海相到泥漿侵入的岩性變化之結果以及穹頂狀地貌的形成表示距今4,700年前左右曾發生海退。藉由斷層兩側的形貌比對配合，我們估計自4100年以來的平均水平偏移量為 54.4 ± 6.0 公尺，斷層的水平滑移速率為每年 13.2 ± 1.6毫米。利用斷層上不同層的垂直偏移量可導出自一萬年以來斷層的垂直滑移率為每年 4.4 ± 1.9毫米。本研究估算的水平滑移速率較2015-2018年GPS估算值來得小。由垂直斷層剖面中生長地層的位移也暗示發生了破裂事件，即滾水坪可能曾發生過地震。然而，上部的生長地層也暗示著可能存在部分的潛移斷層。;Mud volcanoes are commonly found in tectonically compressed environments all around the world. In southwestern Taiwan, mud volcanoes are common near the axis of faults and anticlines in the Coastal Plain and Western Foothills, where the geology is dominated by the 3-5 km-thick Gutingkeng mudstone formation, which is late Miocene to Pleistocene in age. The Lower Gutingkeng mudstone formation was described as a weak sedimentary rock formation, rich in overpressured fluids that could explain the presence of active mud volcanoes. InSAR and GPS observations suggest the existence of a southwest striking right-lateral strike-slip fault in the Holocene Coastal Plain. The inferred fault trace is associated with a topographic scarp and with the presence of the Gunshuiping mud volcano (Yanchao district, Kaohsiung), which displays a dome-shaped topography. The dome-shaped topography is cut by the scarp and appears to be right-laterally shifted, which might be related to the fault activity. In addition, the vents of mud volcano are all located on the southeast block and along the fault trace. This leads us to investigate the kinematics of the active fault and its relation with the formation of the mud volcano. We consider two possible scenarios for the formation of mud volcanoes: mud migrating upwards through faults or fractures or through ductile “piercement”. We investigated the deformation of buried Holocene strata using 19 shallow boreholes, radiocarbon (14C) dating, U-Th dating and Resistivity Image Profiling (RIP) data for stratigraphic correlation across and along the inferred fault. The fault-perpendicular cross-sections show that the bedrock unit and Holocene strata have been uplifting on the southeast block along a fault dipping 70o to the southeast. Meanwhile, the fault-parallel cross-sections show the 4.7 ka buried layers lying sub-horizontally, in contrast to the dome-shaped topography, indicating that the maximum age of the topography is 4.7 ka. The core observations show the 4.7 ka layer as the marine sediments with mud intrusions. Moreover, the layer above it consists of silty clay layers with mud flows, the base of this layer is dated 4.1 ka. Hence, we proposed that the dome-shaped topography is the result of mud flows at the surface with mud-fluid migrating through fractures or faults in 4.7 ka layer. The change in lithology from marine sediments to mud-intruded sediments and the formation of the dome-shaped topography indicate the marine regression around 4.7 ka. By matching the morphology on both sides of the inferred fault, we estimated an average horizontal offset of 54.4 ± 6.0 m and a horizontal fault slip rate of 13.2 ± 1.6 mm/yr since 4.1 ka. Using the vertical offset of distinct layers across the fault leads to a vertical fault slip rate of 4.4 ± 1.9 mm/yr since 10 ka. The horizontal slip rate in our study is slightly smaller than the horizontal slip rate from GPS estimate of 15-20 mm/yr in period of 2015 to 2018. Growth strata visible on the fault-perpendicular profiles, suggest that earthquake events could have occurred at the Gunshuiping site. The growth strata in the upper layer, however suggest the possibility of a recent creeping fault.
Appears in Collections:	[應用地質研究所] 博碩士論文

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