基于噪声面波直接反演法研究天山中段地壳S波速度结构

Crustal S-wave velocity structure of the middle TianshanMountains based on the direct inversion methodof ambient noise surface wave

天山造山带是新生代以来复活隆升的陆内造山带,强烈的地震活动性使得理解和认识天山造山带深部结构及盆山耦合关系尤为重要。文章中使用天山造山带及邻区(40°~49°N,79°~93°E)85个台站2017—2019年的背景噪声资料,结合背景噪声互相关方法获得了6~52 s瑞利波相速度频散曲线,利用基于射线追踪的面波直接反演法对天山中段地壳三维S波速度结构及盆山耦合关系进行研究。结果显示:地壳浅层S波速度分布与构造单元中沉积层厚度相关,塔里木盆地北缘、准噶尔盆地南缘表现为低速,天山造山带表现为高速;到了中下地壳,天山造山带下方存在被高速异常包裹的低速体;莫霍面附近,天山造山带表现出相对低速;准噶尔盆地南缘和天山造山带的地壳厚度分别在45~50 km、50~62 km之间,沿南北向,天山造山带莫霍面呈现较为宽缓的形态;在82°~86.5°E之间,塔里木盆地和准噶尔盆地向天山下方双向俯冲,86.5°~88°E之间,准噶尔盆地向天山南向俯冲,由西向东,不同盆山耦合关系揭示了新生代以来天山中段不同区域构造运动差异,为进一步探讨造山动力过程提供参考。

The Tianshan orogenic belt is an intracontinental orogenic belt that has been revived and uplifted since the Cenozoic.Thus,understanding and appreciating the deep structure and basin-mountain coupling relationships in Tianshan orogenic belt are particularly important due to the strong seismic activity.The phase-velocity dispersion curves of the 6-52 s Rayleigh wave were obtained in this paper using the cross-correlation method of ambient noise based on the ambient noise data from 85 stations in the Tianshan orogenic belt and adjacent areas(40°-49°N,79°-93°E)during 2017-2019.The direct inversion method of surface waves based on ray tracing was employed to investigate the 3D crustal S-wave velocity structure and basin-mountain coupling relationship in the middle Tianshan Mountains.Results show that the S-wave velocity distribution in the shallow crust is related to the thickness of sedimentary layers in the tectonic unit,demonstrating low velocity in the northern margin of Tarim Basin and the southern margin of Junggar Basin and high velocity in the Tianshan orogenic belt.Low-velocity bodies wrapped by high-velocity anomalies below the Tianshan orogenic belt are found in the middle and lower crusts;the Tianshan orogenic belt shows relatively low velocities near the Moho surface.The crustal thicknesses of the southern margin of Junggar Basin and the Tianshan orogenic belt are in the range of 45-50 and 50-62 km,respectively.Between 82°-86.5°E,Tarim and Junggar Basins are subducted bidirectionally below Tianshan Mountains;between 86.5°-88°E,the Junggar Basin is subducted southward to Tianshan Mountains.From west to east,different basin-mountain coupling relationships reveal the difference in tectonic movement in different regions of the middle Tianshan Mountains since the Cenozoic,thus providing a reference for further exploration of orogenic dynamical processes.