【作者】 周民都；

【导师】 曾融生； 王椿镛；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理学， 2005， 博士

【摘要】 本文回顾了地球物理反演和层析成像的发展历史,阐述了地球物理反演和层析成像的国内外研究现状。 本文的研究区域是32°-40°N,100°-108°E。在中国地质构造图上,这个地区属青藏块体东北缘和鄂尔多斯地块西南缘。这里断裂丛生,构造活动强烈,地震发生频繁。 本文利用人工地震测深和天然地震资料反演得到莫霍面深度的数据给出了研究区内莫霍面的等值线图。研究区内的地壳厚度总的趋势是西南厚,东北薄。地表的断裂和莫霍面形态有很多地方吻合的相当好,说明本区的许多断裂是超壳断裂,只是在莫霍面上呈现出断距和产状的差异。 本文使用了甘肃、青海、宁夏、陕西和四川台网的130个台站记录到的从1980年到2002年的3229个区域地震(Ms≥1.5)和168个远震资料。从55024个区域地震震相中挑选出了51210个最大走时残差为3.0s的震相,选取了2651个远震震相。利用赵大鹏博士提供的计算程序进行反演。根据资料的分布情况,并经过多次检测板试验,认为在水平方向上以0.5°×0.5°等间隔划分网格;深度方向,从地表到80km深度,划分了1、10、30、50、65和80km共6层,能够得到较好的反演结果。 层析成像结果显示:1)青藏高原东北缘地区下地壳存在大范围的P波速度低速异常,上地幔顶部多数地区平均P波速度为8.05km/s左右,接近于大陆下方全球的P_n波平均速度8.1km/s,使得莫霍间断面比较清晰,莫霍面反射波能量较强。2)本研究区内发生大震的震中大多位于10km深度图中的低速区、30km深度图中的高速区附近和50km深度图中的低速区附近,表明这些地区有条件形成地震活动带的孕震区。3)青藏高原东北缘地区的主要断裂带均是逆冲兼走滑断裂,它们多数位于速度正负异常的过渡区上,且很可能是超壳断裂。4)从张掖经海原、平凉再向南拐的弧形地带可能就是青藏高原的边缘地带;且预示着阿拉善地块有地台活化的迹象。5)从层析成像结果中切出的二维速度扰动剖面与人工地震测深剖面对比得到较好的吻合。更多还原

【Abstract】 This dissertation first reviews the history of geophysical inversion and seismic tomography and the present status of geophysical inversion and seismic tomography research in China and the world.The research region of this dissertation is 32° - 40° N and 100° - 108° E. In China geological and tectonic map, this region is referred to as the northeastern margin of the Qinghai-Tibetan Block and southeastern margin of the Erdos Platform, where is characterized by intense tectonic activity, many large-scale active faults and frequently occurring earthquakes.Based on the inversion result from deep seismic sounding and natural earthquakes, this dissertation gives out the contour map of Moho interface in the research region. The thickness of crust in this region gradually reduces from southwest to northeast. Fault distribution on the ground surface agree well with the contour of the Moho interface in many areas, which indicate that many faults in this region are ultra-crustal faults and the breaking distance and mode of occurrence of faults display differences only on the Moho interface.The seismic data used in this dissertation are 3 229 local earthquakes (Ms>1.5) and 168 teleseismic events occurred during 1980 to 2002 recorded by 130 seismic stations from seismic networks of Gansu, Qinghai, Ningxia and Sichuan. The seismic phases used are 51 210 local phases with the maximum travel time residual of 3.0 s selected from 55 024 local phases and 2 651 teleseismic phases. The tomographic inversion was calculated using the program codes provided by Dr. Zhao Dapeng. According to the data distribution and several check-board tests, reliable inversion results are obtained for a model with grid size of 0.5° by 0.5° in the horizontal directions and 6 layers of 1, 10, 30, 50, 65 and 80 km deep from the surface to 80 km in the depth.The tomographic inversion results show that: Lower P-wave velocity anomaly exists widely in the lower crust beneath the northeastern margin of the Qinghai-Tibetan plateau. Average P-wave velocity in most of the top of upper mantle更多还原