摘要

2006年9月，我們使用達觀艦從西向東橫跨北呂宋島弧、花東海盆、加瓜海脊與西菲律賓海盆約224公里的測線施放十座輕巧型海底地震儀，並以海研一號接收24頻道的反射震測資料。本研究先利用反射震測資料和重力反演的密度模型建立沉積層與地殼初始模型，然後選取海底地震儀水壓與垂直分量資料的首波、折射波與反射波走時，以剝層法反演沉積與地殼速度模型。從沉積層P波速度模型顯示加瓜海脊的東側海槽與花東海盆沉積層厚度分別約為3公里與4公里厚。至於地殼P波速度模型則顯示加瓜海脊地殼約為14公里厚，而其東西兩側的地殼則分別為7公里和10公里厚。我們也發現加瓜海脊兩側（4.4~5.4公里/秒）與花東海盆（4.2~5.2公里/秒）基盤的P波速度變化大、加瓜海脊的地殼速度（4.8~6.5 公里/秒）高於其附近的上部地殼速度（4.4~5.6 公里/秒），且與北呂宋島弧東側地殼有一明顯的速度分界。我們認為加瓜海脊的東西兩側及花東海盆下方皆有斷層帶，且海脊東西兩側的地殼構造是不對稱的，因此本研究支持前人所提：加瓜海脊是因菲律賓海板塊西北方向聚合擠壓而隆起。

Abstract

Ten Micro-Ocean-Bottom Seismometers (MicrOBS) and a Multi-Channel Seismic (MCS) profiling were implemented across the Gagua Ridge in September 2006. First, an initial model was built from reflection times of the MCS data and a density model inverted from gravity data. Subsequently, we picked refracted and reflected arrivals from four-component OBS data to invert the velocity-interface structure layer-by-layer. Sedimentary model based on OBS/MCS data shows that the largest thickness of the Huatung Basin and the Eastern Trough of Gagua Ridge are about 4 km and 3 km, respectively. Two thrust faults, one west dipping about 45 degrees beneath the Eastern Trough and another east dipping 60 degrees beneath the Western Trough, are imaged in the active basement near the Gagua Ridge. East of the Gagua Ridge, the small velocity variation but with large velocity (about 5.5~6.0 km/s) of the upper crustal structure is observed whereas the large velocity variation but with small velocity (about 3.5~5.0 km/s) is found west of the Gagua Ridge. We also observed from the OBS model that the crust is thicker about 14 km thick below the Gagua Ridge, but it remains about 9~10 km thick as the normal oceanic crust on the both sides of the Gagua Ridge. We conclude that the asymmetrical structures west and east of the Gagua Ridge and formation of the Gagua Ridge within the oceanic crust imaged from OBS data may have resulted from compression due to the northwest convergence of the Philippine Sea Plate east of Gagua Ridge.

目錄
誌謝 ................................................... Ⅰ
摘要 ................................................... Ⅲ
Abstract .............................................. Ⅳ
圖目 ................................................... Ⅷ
表目 ................................................... Ⅹ

第一章 前言 ...............................................
1-1 西菲律賓海板塊區域地體構造 ............................ 01
1-2 台灣東南海域加瓜海脊地體構造的研究 ..................... 03
1-3 前人研究 ............................................ 05
1-4 研究目的 ............................................ 08
1-5 研究測線：跨越加瓜海脊之A測線 ......................... 09
第二章 海底地震儀資料處理 ...................................
2-1 海底地震儀資料簡介 ................................... 11
2-2 海底地震儀資料定位與展示 .............................. 13
2-3 建立初始P波速度模型 .................................. 17
2-4 P波走時訊號的選取 .................................... 17
2-5 反演P波速度模型 ........................................
2-5.1 走時反演法 ........................................ 24
2-5.2 剝層法 ........................................... 24
2-6 P波速度模型的正確性 .....................................
2-6.1 比對多頻道資料 .................................... 26
2-6.2 各層的射線分布 .................................... 27
2-6.3 走時誤差轉換深度與速度不確定性 ...................... 28
2-7 泊松比模型 .............................................
2-7.1 初始泊松比模型建立 ................................. 31
2-7.2 轉換波的選取 ...................................... 31
2-7.3 正演泊松比模型 .................................... 37
第三章 結果與討論 ...........................................
3-1 P波速度模型討論 ..................................... 38
3-2 泊松比模型討論 ...................................... 41
第四章 結論 ................................................
4-1 結論 ............................................... 43
4-2 未來研究發展 ........................................ 46
＊參考文獻 .............................................. 47

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