臺灣博碩士論文加值系統

摘要

本研究利用2004及2005年，分別施放在台灣西南海域活動及被動大陸邊緣的海底地震儀(OBS)所接收的空氣槍資料，探討此區域沉積層P波速度構造及海底仿擬反射(BSR)的反射特性。本文處理由法國海洋探測研究所(IFEMER)所研發的30部海底地震儀，所蒐集到全長約120公里的折射震測剖面。其中2004年4條震測線位於活動大陸邊緣，方向為4條南北向及4條東西向，而2005年單一測線則位於被動大陸邊緣，方向為與大陸邊緣垂直的西北-東南向。經過棋盤測試(checkerboard test)探討OBS分佈及空氣槍震源解析能力之後，選取各測線較佳的速度格點後，再利用挑選的初達波走時及速度構造反演程式(Tomo2D)來探求測線下方之二維P波速度構造。結果顯示被動大陸邊緣測線的沉積層P波速度構造側向變化較均勻，BSR反射面深度的變化也較和緩；相反的，活動大陸邊緣測線的速度構造側向變化劇烈，可能是受到褶皺及斷層作用的影響。
本研究根據人工挑選的直達波、複反射波走時、BSR走時、及三者之振幅來計算海床及BSR的反射係數。為了避免幾何效應及折射波的影響，此處使用的振幅資料是支距小於2公里的訊號。根據計算結果，顯示兩個研究區域的海床反射係數分布在0.1~0.25之間，最大值0.47出現在活動大陸邊緣的地形高區位置。相反的，BSR反射係數的最大值位於被動大陸邊緣測站，該區的平均值約為0.12，局部高值在0.15~0.18之間。至於在活動大陸邊緣的BSR反射係數相對較低，大約在0.015-0.05之間。本研究亦利用BSR反射係數探求水合物飽和度分布，被動大陸邊緣測站平均值約為18~24%，活動大陸邊緣測站平均值約為3~8%。因此推論被動大陸邊緣測測站所在區域的天然氣水合物飽和度明顯高於活動大陸邊緣。

目錄
摘要…………………………………………………………………… I.
目錄...…………………………………………………………………V. 圖表目錄...………………………………………………………… VII.
第一章 前言 ………………………………………………….…… 1.
第二章 地質背景 …………………………………………………… 4.
2.1 活動大陸邊緣….……………………………………….……. 4.
2.2 被動大陸邊緣…………………………………………..……. 5.
第三章 海底地震儀資料…………………………………………… 11.
3.1 儀器介紹…………..………………………….……..……. 11.
3.2 資料蒐集………………………….…………………..……. 14.
3.2.1 活動大陸邊緣OBS測線分布………..…..….…………… 14.
3.2.2 被動大陸邊緣OBS測線分布………..…….…………….. 14.
3.2.3 OBS定位……………………..…………………….…..… 17.
第四章 速度構造反演……………………………………….….… 20.
4.1 初達波選取……..………………………………………..… 21.
4.2 BSR走時選取…………..…………………………….…….. 24.
4.3 建立初始速度模型………………………..…………….…. 26.
4.4 速度模型反演……………………………..……………..… 26.
4.5 解析度分析………………………………..……………..… 33.
4.6 活動與被動大陸邊緣沉積層速度構造比較……..…..…… 36.
第五章 反射強度區域變化………………………………………… 38.
5.1 反射係數計算……………………………………………..… 38.
5.2 海床反射係數比較………………………………………..… 42.
5.3 BSR反射係數比較…………………………………….…..… 44.
第六章 討論與結論………………………………………………… 47.
6.1 海床碳酸鹽分布與海床反射係數關係…..……….…….… 47.
6.2 預估水合物飽和度……………………………….…….…… 51.
參考文獻……………………………………………………….…… 54. 附錄I………..……………………………………………………… 60.

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林殿順 (2006) 含天然氣水合物地層的構造與沉積特徵研究， 中央地質調查所報告第95-25-E號。
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