臺灣博碩士論文加值系統

位於臺灣東部海域琉球隱沒帶以南的加瓜海脊，為菲律賓海板塊中最大的線性海脊，並受到菲律賓海板塊往西北移動的影響，加瓜海脊逐漸往北隱沒於歐亞板塊下方，導致此地區複雜的地殼構造。因此，本文分析2009年TAIGER實驗期間，沿著MGL0906-16 (T4)測線收集的長支距反射震測資料及14站海底地震儀四分量震測資料。由於此測線橫跨臺東峽谷、北呂宋島弧、花東海盆、北加瓜海脊及西菲律賓海盆，本研究建立的P波速度與泊松比模型，可探討加瓜海脊附近的地殼構造變化。首先，根據長支距反射震測資料分析的重合前深度移位剖面，建立沉積層P波速度-界面構造。接著，選取海底地震儀水壓及垂直分量資料中的折射與反射訊號走時，並反演降低走時誤差值，而得到較可信的地殼P波速度-界面模型。進一步，我們選擇基盤及上、中部內地殼界面與莫荷面為P-S波轉換面。然後，從海底地震儀水平分量資料，挑選可辨識P-S轉換波訊號走時，再調整地殼泊松比模型的區塊，以降低P-S轉換波訊號的走時誤差，分析出較可信的地殼泊松比模型。從地殼P波速度-界面模型顯示，花東海盆之地殼 (約9.5公里)厚度較西菲律賓海盆 (約8公里)厚，可能受到菲律賓海板塊向西北擠壓，導致加瓜海脊東西兩側地殼厚度不同。且在北加瓜海脊頂端發現低速帶 (4.0-4.7公里/秒)，可能是變形帶、破碎帶或斷層帶。另一方面，在花東海盆下方的下部地殼發現高速帶 (約7.5-7.9公里/秒)與相對低的泊松比值 (0.243-0.255)，可能為岩漿入侵造成的火成岩體。最後，由於菲律賓海板塊向北隱沒至歐亞板塊底下，因此從整合的沉積物與地殼厚度分布圖中，發現地殼厚度向北逐漸變厚 (約16公里)。加瓜海脊底下地殼厚度 (15-17公里)較東西兩側厚，並逐漸向北隱沒至琉球海溝下方。而且加瓜海脊附近的地殼皆受橫移壓縮 (transpression)作用的影響，導致許多平行海脊的破碎帶在加瓜海脊頂端與兩側形成。更進一步，觀察到在花東海盆底下多處岩漿入侵造成的火成岩體，其來源可能為加瓜海脊之初始隱沒造成岩漿入侵。因此，加瓜海脊可能為初始隱所形成之海脊。

Gagua Ridge, the largest linear ridge in the western part of the Philippine Sea Plate off eastern Taiwan, is northward subducted beneath the Eurasian Plate in the Ryukyu subduction zone. In this study, we analyzed 14 four-component ocean-bottom seismometer (OBS) data along MGL0906-16 (T4) line of the 2009 TAIGER experiment to build a P-wave velocity model and a Poisson’s ratio model across the northern Luzon Arc, the Huatung Basin, the Taitung Canyon, the northern Gagua Ridge and the West Philippine Basin off eastern Taiwan. Firstly, P-wave velocities and interfaces of the sedimentary layers were built by considering a pre-stack depth-migrated (PSDM) model analyzed from the long-offset reflection data. Secondly, the refracted and reflected arrivals, propagating through the crustal structures, picked from OBS data layer by layer were used to invert the P-wave velocities and interfaces of the crustal model, respectively. Models of P-wave velocities and interfaces enabled us not only to build initial models of Poisson’s ratio but also to set up the converted interfaces (such as basement, intra-crust and Moho interfaces) for shear-wave modeling. Finally, we identified the phases of the converted shear waves and picked their travel-times from two horizontal components of OBS data to invert the Poisson’s ratio model. Based on the crustal models, crustal thickness below the Huatung Basin (about 9.5 km) is thicker than that below the West Philippine Basin (about 8 km) due to northwestward compression of the Philippine Sea Plate. The low P-wave velocity zone (4.0-4.7 km/s) in the Gagua Ridge may be owing to deformation, fractures or faults. On the other hand, caused by magma intrusion of igneous rocks are found in the middle and lower crust below the Huatung Basin as shown by a high P-wave velocity zone (about 7.5-7.9km/s) and relatively low Poisson’s ratio (0.243-0.255). Based on the map of the sedimentary and crustal thickness, crustal thickness is northward increased (about 16 km) since Philippine Sea Plate is subducted beneath Eurasia Plate. Furthermore, the crustal thickness below the Gagua Ridge is thicker (15-17 km) than two sides of it, and the Gagua Ridge is northward subducted beneath Philippine Sea Plate. The fracture zones, parallel the Gagua Ridge, are observed at top and both sides of the Gagua Ridge by transpression. We also observed caused by magma intrusion of igneous rocks below the Huatung Basin. Therefore, we suggested that the Gagua Ridge might be formed by initial subduction.

摘要 I
Abstract II
目次 III
圖次 IV
表次 VI
第一章 前言 1
1-1 臺灣東部海域地體構造 1
1-2 加瓜海脊地體構造 3
1-3 臺灣東部海域地體泊松比 6
1-4 研究目的與區域 8
1-4-1 研究目的 8
1-4-1 研究區域 9
第二章 海底地震儀資料處理 10
2-1 海底地震儀定位 10
2-2 海底地震儀四分量資料 13
第三章 研究方法 16
3-1 初始P波速度模型 16
3-2 海底地震儀水壓與垂直分量資料走時選取 19
3-3 反演P波速度模型之走時誤差 29
3-4 地殼泊松比模型 31
3-4-1 轉換波類型 31
3-4-2 海底地震儀水平分量走時選取 37
3-4-3 正演泊松比模型之走時誤差 42
第四章 結果與討論 44
4-1 地殼P波速度模型 44
4-2 地殼泊松比模型 52
4-3 沉積物與地殼厚度 55
第五章 結論 58
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