菲律賓海板塊高解析剪力波速度影像和非均向性研究

High resolution shear-wave velocity imaginary and anisotropic study beneath the Philippine Sea Plate.

張文彥(Wen-Yen Chang)

指導教授 ： 余貴坤 ； 王乾盈

國立中央大學/地球科學學院/地球物理研究所/博士(2006年)

摘要

本研究共分析1057個地震，超過3000條表面波的地震記錄，以多重濾波法、相位匹配法和赫伯轉換法，獲得週期20秒~120秒雷利波的群速及相速，並配合純路徑法及區塊逆推（20x20），探求高解析度菲律賓海板塊的群速和相速頻散層析分布。結果清楚顯示菲律賓海板塊的地質特徵及盆地演化過程相當吻合，包括菲律賓海板塊周圍為活動構造或碰撞隱沒帶，高熱流活動、岩漿作用等現象，呈現低速的分布。West Philippine Plate和Parece Vela Basin出現明顯的高速，此現象反應海洋板塊上部地函的構造，West Philippine Basin的高速出現在Central Basin Fault 兩側，即與擴張中心兩側對應型態，隨週期變大，高速區向南北推移此結果和西菲律海盆的演化及形成過程一致。反演的高解析三維剪力波速度構造，顯示30公里深的菲律賓海板塊東北部和西南部有明顯的低速，表示Ryukyu trench和Philippine trench仍有很高的熱流活動，其次東部活動邊緣速度比板塊內部均低；高速出現在西菲律賓海盆和Parece Vela Basin，最高可以達4.8公里/秒，在中央盆地斷層（擴張中心）兩側形成對應的高速區，這和西菲律賓海板塊由擴張中心向兩側擴張形成的演化歷史相吻合，西菲律賓海盆和Parece Vela Basin演化較早，應有較厚的岩石圈或存在高速帶。
非均向性研究發現板塊內主要盆地存在顯著的非均向性，此特性和盆地演化有密切的相關性；在西菲律賓海盆地、Parece-Vela、Shikoku存在明顯的速度非均向性而且其快波方向(東北-西南)與海盆演化過程張開方向一致(即與中央盆地斷層垂直)。Parece-Vela、Shikoku盆地快波方向(東北-西南)也與板塊張開方向一致，Palau Kyushu ridge非均向性較不明顯，但大致平行構造走向，但東部活動構造邊緣和東北部琉球隱沒帶存在顯著的非均向特性，快波方向和板塊邊界也大致平行。
岩石圈的厚度與地質年代、演化過程有密切關聯，利用板塊冷卻模式將本文與前人研究之岩石圈厚度換算成演化年代作一比較，發現西菲律賓海盆岩石圈厚度約50公里，Parece Vela Basin岩石圈厚度約38公里和Shikoku Basin則為35公里。此結果和其他地磁、重力、地球化學定年的調查研究最合理，進而確認盆地演化的歷史。

關鍵字

非均向性 ； 剪力波速度 ； 菲律賓海板塊

並列摘要

In this study, the group and phase velocities of more than 3000 Rayleigh wave paths across the Philippine Sea Basin and its surrounding area are determined at the periods between 20 and 120 seconds. To investigate the lateral variation of shear velocity, the study area is divided into 399 blocks with the block size of 2 x 2 , and the group and phase velocity dispersions in each block are also derived by the pure-path method, respectively. By inversion of these dispersion data, high-resolution shear velocity structures along several east-west and north-south profiles of the Philippine Sea Basin are deduced. The results reveal the major geological structural features of the basin and its surroundings. The plate thickness is about 50 km in the western Philippine Sea Basin and 35 to 38 km in the Shikoku and Parece-Vela Basins. These results consistent with the basin evolution described in previous studies and quite match the values estimated by the cooling model of the plate. The azimuthal anisotropy is also derived in the study. The fast velocity directions are roughly agree with the spreading motions given by the ocean-floor topographic features.

並列關鍵字

anisotropy ； shear-wave velocity ； Philippine Sea Plate

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