利用面波频散和接收函数联合反演中国境内天山及邻区的地壳上地幔速度结构

JOINT INVERSION OF SURFACE WAVE DISPERSION AND RECEIVER FUNCTIONS FOR CRUSTAL AND UPPERMOST MANTLE STRUCTURE BENEATH CHINESE TIENSHAN AND ITS ADJACENT AREAS

天山造山带是现今世界上最活跃的陆内造山带之一,研究这一地区的壳幔深部结构对认识天山造山深部动力学过程具有重要意义。文中利用新疆测震台网52个固定地震台站和在天山地区新布设的11个流动地震台站为期1a的观测数据,采用背景噪声层析成像方法获得了中国境内天山及邻区(41°~48°N,79°~91°E) 10~50s周期范围内瑞利(Rayleigh)面波的相速度分布图像,通过面波和接收函数联合反演揭示了中国境内天山地区(41°~46°N,79°~91°E)的地壳上地幔S波速度结构和台站下方的地壳厚度。结果表明,在天山北部和天山南部盆山接触带附近的地壳内部存在多个明显的低速层,北部边缘和南部边缘的壳内低速区结构特征及分布范围存在明显差异。结合前人的相关研究结果,我们推测塔里木盆地和准噶尔盆地向天山造山带的俯冲主要发生在中国境内天山造山带的中部,其中天山南缘的俯冲比北缘的范围大,东部地壳的俯冲不明显或处于俯冲的早期阶段。天山造山带内部的地壳存在多个低速层分布的地区,它们大多与目前正在发生强烈隆升的区域相对应。文中得到的S波速度结构可为天山造山带的分段性及盆山耦合类型的差异性等研究提供新的深部依据。

The Tienshan orogenic belt is one of the most active intracontinental orogenic belts in the world.Studying the deep crust-mantle structure in this area is of great significance for understanding the deep dynamics of the Tienshan orogen.The distribution of fixed seismic stations in the Tianshan orogenic belt is sparse.The low resolution of the existing tomographic results in the Tienshan orogenic belt has affected the in-depth understanding of the deep dynamics of the Tienshan orogenic belt.In this paper,the observation data of 52 mobile seismic stations in the Xinjiang Seismic Network and the 11 new seismic stations in the Tienshan area for one-year observations are used.The seismic ambient noise tomography method is used to obtain the Rayleigh surface wave velocity distribution image in the range of 10~50s beneath the Chinese Tienshan and its adjacent areas(41°~48°N,79°~91°E).The joint inversion of surface wave and receiver function reveals the S-wave velocity structure of the crust and uppermost mantle and the crustal thickness below the station beneath the Chinese Tienshan area(41°~46°N,79°~91°E).The use of observation data from mobile stations and new fixed seismic stations has improved the resolution of surface wave phase velocity imaging and S-wave velocity structure models in the study area.The results show that there are many obvious low-velocity layers in the crust near the basin-bearing zone in the northern Tienshan Mountains and the southern Tienshan Mountains.There are significant differences in the structural characteristics and distribution range of the low-velocity zone in the northern margin and the southern margin.Combining previous research results on artificial seismic profiles,receiver function profiles,teleseismic tomography,and continental subduction simulation experiments,it is speculated that the subduction of the Tarim Basin and the Junggar Basin to the Tienshan orogenic belt mainly occurs in the middle of the Chinese Tienshan orogenic belt,and the subduction of the southern margin of the Tienshan Mountains is larger than that of the northern margin,and the subduction of the eastern crust is not obvious or in the early subduction stage.There are many low-velocity layers in the inner crust of the Tienshan orogenic belt,and most of them correspond to the strong uplifting areas that are currently occurring.The thickness of the crust below the Tienshan orogenic belt is between 55km and 63km.The thickness of the crust(about 63km)is the largest near the BLT seismic station in the Bazhou region of Xinjiang.The average crustal thickness of the Tarim Basin is about 45km,and that of the Junggar Basin is 47km.The S-wave velocity structure obtained in this study can provide a new deep basis for the study of the segmentation of the Tienshan orogenic belt and the difference of the basin-mountain coupling type.