論文提要內容： 紅河斷裂帶是東南亞地區一個顯著的構造帶。本文的第一個工作 是研究紅河斷裂帶目前的活動性質。本研究在越南的紅河斷裂帶設置 臨時地震觀測網，收集紅河斷裂帶的地震活動資料，以研究其地震活 動度，並以地震矩張量反演推求地震斷層面解，以了解紅河斷裂帶目 前的滑移性質。 由研究結果得知紅河斷裂帶目前的地震活動微弱，此和野外觀察 推論之滑動速率較低的結果一致。又由研究所得地震斷層面解知紅河 斷裂帶目前的位移為右移且有正斷層分量。由斷層面解也得知，紅河 斷裂帶附近，大地應力分佈應為南北向壓縮，東西向張裂。紅河帶目 前雖無大地震發生，但仍是大地震潛在危險地區。 本研究的第二個工作是藉用東南亞週邊地震的表面波記錄推求 東南亞地區地殼與上部地函之三維剪力波速度構造。。而其方法是利 用表面波群速頻散性質，以區塊逆推法，先把研究區以o o 3 3 ´ 的大小 分成子區塊，再求各子區塊的區域化群速頻散，然後以表面波逆推法 求各個子區塊的剪力波速度構造，最後合併各子區塊剪力波速度構 造，形成東南亞地區的三維剪力波速度構造，其結果顯示東南亞地區 的速度構造具有顯著的橫向不均勻性，這種現象至少持續達110 公里 深。南海海盆的岩石圈厚約70 公里，其蓋層剪力波速約4.4~4.5 公里 /秒，其上部地函低速層之剪力波速可低達4.1~4.2 公里/秒，按其速度 構造南海海盆之南北兩部分具有極佳對稱性，因此南海的張裂模式應 是純剪切式。又南海之下的高速層結構，其洋脊下之速度較周圍高， 與一般洋脊的結構不同，這種差異如何解釋，有待進一步研究。由三 維速度影像推測紅河斷裂帶似是切穿岩石圈的深斷裂，斷層北邊的速 度高於南邊。 The first object of this study is to investigate the activity and the slip characteristics of the Red-River fault zone in Vietnam. A temporary seismic network was deployed around the Red-River fault zone in Vietnam to study the seismicity of Red-River fault zone. The result shows the seismicity of Red-River fault zone in Vietnam is low. From the fault plane solutions calculated by moment tensor inversion, the slip of Red-River fault zone is right lateral with normal fault component. The second object of this study is to calculate the velocity structure of the crust and upper mantle in Southeast Asia. The seismic surface waves from earthquakes around Southeast Asia are analyzed by multiple filter technique for group velocity dispersion of fundamental mode Rayleigh and Love waves. Then, block inversion method was applied to get regionalized group velocity for each block of the research area. Then, surface wave inversion method was applied to invert the shear wave velocity of each block from regionalized group velocity. Finally, the shear wave velocity structure of each block is combined to form the three dimensional shear wave velocity structure of the crust and upper mantle in Southeast Asia. The three dimensional shear wave velocity structure obtained shows the velocity structure of Southeast Asia has significant lateral heterogeneity. The lid velocity of South China Sea is about 4.4~4.5km/sec, the thickness of lithosphere is about 70km and the lowest velocity in the upper mantle low velocity zone is about 4.1~4.2km/sec. The structure of the high velocity layer in South China Sea is quite different from that of the seismic velocity model of middle ocean ridges. The Red-River fault zone is a conspicuous structure in the three dimensional velocity image, it penetrate quite deep, perhaps it cut through the lithosphere.The velocity of northern side of Red-River fault zone is hgher than that of southern side.
