太行山构造带及其以东地区上地幔地震层析成像

Upper Mantle Seismic Tomography Under Taihangshan Tectonic Belt and Areas at Its East

基于首都圈地区及河北邯郸台网共115个台站记录的地方震、近震和远震P波和S波走时,利用地震层析成像技术得到了太行山构造带及其以东地区下方300km深度范围内的P、S波速度结构。结果发现沿太行山构造带速度结构在上地幔中存在明显的横向不均匀性,其南、中、北段显示了各自不同的构造特征。太行山以东盆地区岩石圈厚度较薄,在约80km深度进入地幔软流层,但在160km深度下,P波和S波速度结构呈现较大差异,其中P波在华北东部地区逐渐以高速为主,而S波速度剖面上虽然低速体被切割,但仍然保持了大部分地区的相对低速。深部结构揭示,太行山中段受华北地区岩石圈减薄过程作用最为强烈,其速度结构与盆地区更为相似。而南段构造作用与浅部断裂关系明显,深部可能更多地保留了构造造山带岩石圈厚度大,高速介质多的特征。太行山北段处于多构造交界地区,速度结构比较复杂,部分S波低速区可能与深部地幔物质上涌作用有关。

Based on P and S wave travel times of local,regional and far earthquakes recorded on 115 station distributed in capital area and Handan network in Hebei Province,P and S wave velocity structures beneath Taihangshan tectonic belt and areas at its east were obtained in the depth of 300km by seismic tomography technology.The results show that,there exists obviously transversal unhomogeneous in upper mantle velocity profiles along Taihangshan tectonic belt,where its southern,middle and northern segments exhibits their different structure features.Beneath the area at the east of Taihangshan,the lithosphere is thin,and the asthenosphere here is at the depth of about 80km.But under the depth of 180km,the P wave velocity structures show large differences in S wave velocity structures,in which at the east area of North China there presents mainly high P wave velocity,while S wave velocity maintains relatively low in most areas of North China basins although the low velocity media is cut by high velocity bodies.The deep structures demonstrate that,the middle segment of Taihangshan had been affected strongly by the lithospheric thinning in North China,and its velocity structure is much consistent with that beneath the basins.While the tectonic activity in southern segment was controlled apparently by shallow faults,but the upper mantle may maintain the character of old orogen with thick lithosphere and more high velocity media in upper mantle.The northern segment of Taihang belt,located at the boundary of multi-tectonic area,is complicated in velocity structure,and part low velocity region may be connected with mantle upwelling.