利用背景噪声层析成像方法反演新疆天山及邻区S波速度结构

S-wave Velocity Structure Inversed by Ambient Noise Tomography in Xinjiang Tien Shan and Its Surrounding Areas

摘要:

利用新疆地震台网52个固定台站和天山地区新布设的11个流动台为期1年的观测数据，采用背景噪声层析成像方法获得了天山及邻区（41°～48°N，79°～91°E）10～50s的瑞利面波相速度分布图像，使用基于贝叶斯的马尔科夫链蒙特卡洛（MCMC）方法反演得到研究区地壳上地幔S波速度结构。研究结果表明，准噶尔盆地沉积盖层南深北浅，最厚处可达15km。在天山造山带北部和南部的盆山交界附近，地壳内部存在明显的向造山带方向倾斜的低速区，结合前人相关研究结果，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中部，东西部只存在较弱的单向俯冲。天山造山带下地壳存在明显的低速异常，反映出介质具有较低的力学强度，在挤压环境下更容易发生变形和隆升，下地壳低速异常可能与存在古板块缝合带、天山南北两侧的大陆块体双向俯冲以及挤压变形等密切相关。

Abstract:

With one year data of 52 permanent stations and 11 new temporary stations,we obtained Rayleigh surface wave phase velocity distribution images of cycle 10～50s in Xinjiang Tien Shan and its surrounding areas(41°～48°N,79°～91°E) by ambient noise tomography method. The S wave velocity structure of the earth's crust and upper mantle in the study area is also obtained by using MCMC method based on Bayesian. The results show that the sedimentary cover in Junggar Basin is deep in the south and shallow in the north,and the thickest part can reach nearly 15km. In the vicinity of the basin-mountain junction in the northern and southern parts of the Tien Shan orogenic belt,there exist some clear low-speed zones in the crust that is inclined toward the orogenic belt. Combining previous research results,we speculated the subduction of Tarim Basin and Junggar Basin to Tien Shan orogenic belt mainly in central Tien Shan orogenic belt in China,and eastern and western Tien Shan are only one-way weak subduction. There are obvious low-velocity anomalies in the lower crust of the Tien Shan orogenic belt,which reflect that the medium has low mechanical strength and is more prone to deformation and uplift under the extrusion environment. The low-velocity anomalies in the lower crust may be closely related to the existence of the ancient plate suture belt,and the bidirectional subduction of the continental masses on the north and south sides of the Tien Shan and the extrusion deformation.