利用表面波探討造山帶地區的非均向性構造：以台灣及西藏高原為例; Seismic anisotropy beneath the orogeny from surface-wave analyses: The observations in Taiwan and the Tibetan Plateau

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題名:	利用表面波探討造山帶地區的非均向性構造：以台灣及西藏高原為例;Seismic anisotropy beneath the orogeny from surface-wave analyses: The observations in Taiwan and the Tibetan Plateau
作者:	賴雅娟;Ya-chuan Lai
貢獻者:	地球物理研究所
關鍵詞:	方位非均向性;徑向非均向性;表面波;azimuthal anisotropy;radial anisotropy;surface-wave
日期:	2008-01-08
上傳時間:	2009-09-22 09:53:48 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本研究採用陣列方法及短距離雙站分析方法，分析寬頻地震紀錄的基態表面波相速度，討論西藏及台灣造山帶地區的非均向性構造，以期瞭解地下地層在造山運動過程中的應力應變情形。西藏高原由數個構造組成，其中最主要的構造為南部的拉薩地塊和北部的羌塘地塊，兩者以班公怒江縫合帶分界。本研究分析南北地塊的基態雷力波及洛夫波，結果顯示兩者的相速頻散曲線特徵及剪力波速度模型有相當大的差異，拉薩地塊為正常的地殼平均速度且偏高的上部地函速度，而羌塘地塊為偏低的地殼速度及上部地函速度，以及高達0.3的泊松比，這些特徵表示拉薩地塊為低溫高速的地層，羌塘地塊則處於高溫的環境。另外，地層的徑向非均向性分布也有相當差異，拉薩地塊分布在中部至下部地殼，與該區域普遍觀測到的低電阻及高熱流值相關，暗示拉薩地塊的地殼非均向性來自地層的裂隙或者水平的熔融地層。羌塘地塊非均向性分布在上部地函，應與地層橄欖石受擠壓時長軸在水平方向排列有關。整體而言，利用表面波分析的剪力波速度及徑向非均性分布，高速且均向的拉薩地塊上部地函應為低溫且沒有變形的隱沒印度板塊，低速且強非均向性的羌塘地塊則反應高溫且強烈變形的歐亞大陸板塊，兩板塊應在班公怒江縫合帶附近分界。台灣的中央山脈除以陣列方式分析徑向非均向性外，並分析不同路徑雷力波相速度的方位非均向性，配合兩者非均向性特徵及剪力波分離觀測結果，全面性討論其來源及中央山脈地下構造在造山運動下的應力情形。由長短週期雷力波方位非均向性的差異可知中央山脈非均向性應分成兩層，淺層為東-西向快軸，而深層為東北-西南快軸方向。配合徑向非均向性模型的分布深度分布範圍介於中部地殼與深度150公里之間，推測淺層非均向性來源為地殼中液體充填的裂隙，而深部地層為碰撞應力作用下橄欖石長軸垂直最大應力方向排列。淺層的水平裂隙顯示中央山脈深部地殼目前仍有垂直伸張的應力，也就是說中央山脈仍處於抬昇的狀態從地殼裂隙的排列至深部橄欖石皆受東-西向菲律賓海板塊擠壓的應力作用，且延伸至至150公里的橄欖石非均向性分布，則說明在碰撞過程中中央山脈的地層整體垂直變形包含岩石圈及部分上部軟流圈。 In this study, we attempt to understand the seismic anisotropy beneath the orogeny from the observations of fundamental surface waves. The array analyses were adopted for average phase velocities of Rayleigh and Love waves, respectively. For the observations in the Tibet plateau, the inverted shear-wave structures show the noticeable contrasts between the Lhasa and Qiangtang terranes. The crustal-velocity decreases about 0.3 km/s from south to north with a significant change of Poisson’s ratio from normal value in the south to relative high value in the north. Besides, the mantle is cold and high-velocity of Lhasa but is hot with unusual low velocity of Qiangtang. In north Tibet, the model also shows no obvious lid which indicates the thinning or melting lithospheric mantle. On the whole, the opposite geophysical properties indicate the mantle lithosphere is not identical from south to north of the Tibet plateau. The Love-Rayleigh discrepancies reveal the radial anisotropies varying with depth to infer the feasible origin of anisotropy. The radial anisotropy is derived within the mid-to-lower crust beneath southern Tibet and is related the fluid-filled cracks or the horizontal partial-melting layer. The anisotropy is inferred within the upper mantle beneath northern Tibet and is coincident with the shear-wave splitting, which is considered as the results of alignments of olivine. For the phase velocities revealed by the modified two-station method, the azimuthal anisotropy parameters of the Central Range show significant variations with period. The upper layer is displayed by the anisotropic terms of short -period signals, characterized with fast polarization in east-west direction, and is related to the crustal cracks. In contrast, the lower layer is retrieved by the extensive long-period signals and is characterized with fast polarization in approximately northeast direction. The mantle anisotropy is commonly regarded as the olivine alignments accommodated to the compression or transcurrent motion during plate collision. The mantle anisotropy extending to 150 km deep demonstrates the anisotropic properties beneath the Central Range and corresponds with the fast direction and large time-delay revealed from the shear-wave splitting.
顯示於類別:	[地球物理研究所] 博碩士論文

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