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利用ASCENT计划于2007年布设在青藏高原东北缘的18个宽频带流动台站约一年的观测资料获得了2547个接收函数.使用H-?域的搜索算法,得到了14个台站下方的地壳厚度.对于数据质量较差的3个台站,通过Moho的Ps转换波的到时估算出地壳厚度值.计算结果表明,研究区的地壳结构复杂,Moho深度变化范围为40~60 km.海原断裂附近Moho模糊,而且较两侧明显地加深.秦祁地块由西向东Moho逐渐变浅,105°E以东,Moho平均深度约为45 km,以西则在50 km以上.结合面波研究结果推测,在105°E附近可能存在一个秦岭与祁连分界线.以Crust 2.0作为初始模型,把计算得到的地壳厚度值作为约束,用线性反演方法得到了15台站下方的S波速度结构.通过与研究区人工源地震测深结果比较,发现二者具有较好的一致性,表明反演结果可靠.综合分析认为:在青藏高原区,青藏高原与西秦岭过渡带和西秦岭北段均存在中下地壳低速层,推测它们可能与附近断裂和深部物质运移有关.从青藏高原内部到边缘,中下地壳速度逐渐升高.再结合研究区地壳的速度(尤其是低速层)的分布特点以及与地壳物质成分相关的泊松比的变化规律等综合分析,认为地壳流在青藏高原东北部的边缘地带可能不存在,地壳可能是通过在挤压方向上的缩短而加厚.
A total of 2547 receiver functions have been obtained using the ASCENT program in 18 broadband stations in the northeastern margin of the Qinghai-Tibet Plateau distributed in 2007. Using the H-domain search algorithm, 14 The thickness of the crust The thickness of the crust was estimated by Moho’s Ps conversion wave for three stations with poor data quality.The calculated results show that the crustal structure of the study area is complex and the Moho depth varies from 40 km to 60 km. The Moho near Haiyuan fault is fuzzy and obviously deeper than the two sides. The Qinqi block gradually becomes lighter from west to east at Moho, east of 105 ° E, Moho average depth is about 45 km and west is above 50 km. The results suggest that there may be a boundary between Qinling and Qilian near 105 ° E. Using Crust 2.0 as the initial model and the calculated crustal thickness as a constraint, S-waves below 15 stations are obtained by linear inversion Velocity structure.Comparing with the result of artificial source seismic sounding in the study area, it is found that the two have good consistency, which shows that the inversion result is reliable.A comprehensive analysis shows that: in the Qinghai-Tibet Plateau, the Qinghai-Tibet Plateau and the West Qinling transitional zone and the West Qinling North section are present Lower crust low-velocity layer, suggesting that they may be related to the nearby faults and deep material migration.From the interior to the edge of the Qinghai-Tibet Plateau, the crustal velocity is gradually increased.Combined with the distribution of the crustal velocity (especially the low velocity layer) in the study area and Based on the comprehensive analysis of the Poisson’s ratio variation related to the crustal material composition, it is considered that the crustal flow may not exist in the northeastern part of the Qinghai-Tibet Plateau. The crust may be thickened by the shortening in the extrusion direction.