利用重力資料探討台灣及其鄰近地區之三維地下構造; The 3D tectonic structures of Taiwan and surrounding areas from gravity data

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Title:	利用重力資料探討台灣及其鄰近地區之三維地下構造;The 3D tectonic structures of Taiwan and surrounding areas from gravity data
Authors:	謝獻祥;Hsien-Hsiang Hsieh
Contributors:	地球物理研究所
Keywords:	布蓋重力異常;台灣;重力;莫荷面;密度構造;gravity;Taiwan;density structure;Bouguer anomaly;Moho
Date:	2009-07-07
Issue Date:	2009-09-22 09:54:16 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	台灣及其鄰近區域位處歐亞板塊與菲律賓海板塊之間，受到擠壓、碰撞及隱沒等地體動力作用，側向地下構造變化複雜。為解決地體構造問題，目前以地震學研究為大宗，但因地震測站架設的多寡與分佈方式，造成淺層地下構造解析下降與可信度不足的問題，雖可加入更多地震測站與資料來輔助解釋，仍有盲點存在。當務之急是加入其他物理量增加控制，而重力研究即是一項經濟且快速的方法，尤其大尺度的重力研究與三維密度構造解釋是十分必要與亟需的。首先建立台灣重力資料庫，可避免許多早期珍貴的野外施測紀錄因時間久遠而遺失，本研究整理台灣中油公司共約八萬多點重力測點與中研院地球所量測全台重力資料包含山區與平地共603點。經過資料檢視、測點高程與測點鄰近重力值比對之後，重新配合數位地形模型進行重力修正流程，最後彙整兩筆重力資料可得到完整分布全台灣平地到山區的重力資料庫，繪出台灣新修正版之布蓋重力異常圖，提供後續許多區域性與大尺度構造研究所使用。台灣海峽莫荷面深度研究中，經過各方資料整理之後，求得台灣海峽重力異常，消除海水層與海底地形起伏效應，得到台灣海峽區域布蓋重力異常。代入Parker-Oldenburg 關係式計算莫荷面深度，整體莫荷面起伏平緩在30km 上下，由西北往東南為厚-薄-厚分佈，最淺莫荷面深度出現在澎湖島下方，約27-28km 深。台灣本島三維地下密度構造研究中，利用重力資料檢驗前人提出三種不同速度模型，挑選其中最符合重力觀測的速度構造，配合地表地質分區建立地下密度初始模型，利用最小平方法進行逆推，計算出地下密度模型。結果顯示台中與高屏盆地出現數公里厚的沉積層；在10km 深處，東台灣出現高密度海洋性地殼，西台灣發現北港高區基盤。台灣下方莫荷面以中央山脈下方最深，往兩側變淺，東部梯度變化快速，西部梯度變化較緩。未達到完全補償，深度不超過45km。 Taiwan, located in the collision and subducting area, has complex tectonic background. For further understanding of the complex structure beneath Taiwan and its surrounding area, besides seismic and geologic study, gravity study also provides useful geophysical information to redeem the lack resolutions in the shallow depths in seismology. The Taiwan Strait gravity anomaly map is constructed by combining marine and land data from Taiwan, Fuchien Province in China, Removing gravity effects generated by the water layer and seafloor topography, the regional Bouguer gravity anomaly is obtained. Moho depth is then computed by the Parker-Oldenburg iterative method from the regional Bouguer gravity data set. Over the strait area, the Moho relief is generally flat with an average depth of about 30 km, and the shallower Moho depth reaches up to 28 km beneath the Penghu uplift. Moho depth is relatively shallower in the middle Taiwan Strait and thickens toward both sides of the strait. For further regional and large-scale tectonic research, the gravity database of Taiwan is composed from CPC company and IES Academia Sinica dataset. After data checking and new gravity correction, the new Bouguer anomaly map and gravity database are obtained. The Taiwan new bouguer anomaly map is presented to compare with the calaulated anomaly map from corresponding density distributions by converting from three P-wave velocity models according to the referenced formula. After 3-D gravity inversion, the result indicates that the sedimentary layers are thicker in Taichung and Kaoping basins and the deepest Moho depth beneath Central Range is shallower than 45 km.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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