基于背景噪声成像法研究土耳其中部岩石圈速度结构

面波成像是研究岩石圈速度结构的有效方法，但基于地震事件面波数据的传统成像方法因面波数据周期长、地震定位不准确、以及地震时空分布不均等因素难以对地壳内部结构有效成像。近二十年间发展起来的基于背景噪声的面波成像法有效地克服了上述传统地震方法的缺点，提高了面波成像的空间分辨率。陈晓非课题组提出的频率-贝塞尔变换法能够高效准确地提取面波高阶频散曲线，拓宽频带，为反演提供更多约束信息，降低反演的非唯一性，极大地提高了面波反演的精度。

土耳其东部是由大陆碰撞引起的挤压变形，而西部则为俯冲引起的爱琴海伸展变形，土耳其中部作为两者之间的过渡，此区域拥有复杂的地质情况、火山作用和长远的俯冲、大陆碰撞等构造历史，为了更好地了解土耳其中部的岩石圈速度结构，本文遵循背景噪声成像的处理流程，利用改进的频率-贝塞尔变换法提取频散曲线，结合基于BFGS矫正的拟牛顿迭代反演方法得到此地区0～124 km深的高分辨率三维剪切波速度结构。结果表明，土耳其中部速度横向变化剧烈，速度界线与地质边界或缝合带区域密切相关；从塞浦路斯海沟开始俯冲的非洲大洋岩石圈，以近垂直角度俯冲在金牛座山脉中部下方，表现为明显的高速特征；此区域在70～100 km广泛存在与上升软流圈物质相关的低速带，因此大部分研究区域的岩石圈波速小于全球平均剪切波速度，并且此区域岩石圈整体较薄，厚度多变；金牛座山脉中部和东部在中地壳的低速带十分明显，推测可能和块体破裂导致的地层部分熔融有关。

本文利用改进的频率-贝塞尔变换法得到的土耳其中部的三维剪切波速度结构具有很高的分辨率，为该区域的深入研究提供了可靠的数据支持，对进一步认识该区域的构造运动及其演化过程具有十分重要的指导意义。

Surface wave tomography is an effective means to study the shear wave velocity structure of the lithosphere. However, traditional surface wave imaging methods based on seismic events have difficulties in effectively imaging the internal structure of the crust, given that long period of surface wave data from seismic events, inaccurate seismic location and unevenly spatio-temporal distribution of earthquakes. Ambient noise tomography developed in recent 20 years effectively overcomes the shortcomings of the above traditional seismic methods, and greatly improves the spatial resolution of surface wave imaging. The frequency-Bessel transform method proposed by Chen Xiaofei’s research group can efficiently and accurately extract the multimodal surface wave dispersion curve and broaden the frequency band. Therefore, this method provides more constraint information for inversion, reduces the non-uniqueness of inversion and greatly improves the accuracy of surface wave inversion.

Central Turkey represents the transition between extrusion deformation of eastern Turkey caused by continental collision and extension deformation of western Turkey caused by continuous subduction along the Aegean trench. This region has complex geological conditions, volcanism and long-term tectonic history of subduction and continental collision. In order to understand the lithospheric velocity structure in central Turkey, we follow the processing procedure of ambient noise tomography and extracts dispersion curves by using modified frequency-Bessel transform method. Then we obtain the high-resolution 3D shear wave velocity structure at the depth of 0 ~ 124 km by using Quasi Newton iterative inversion method based on BFGS correction. The results reveal that the lateral variation of velocity in central Turkey is intense, and the velocity boundary is closely related to the geological boundary or suture zone. The African oceanic lithosphere, which began to subduct from the Cyprus trench, subducted below the central Taurus Mountains at a near vertical angle, showing high-speed characteristics. Low velocity zones related to upwelling asthenosphere materials widely exist within the depth range of 70-100 km in this region. Therefore, the lithospheric wave velocity in most of the study areas is less than the global average shear wave velocity, and the lithosphere is thin and variable; The low velocity zone in the middle crust is obvious in the Central Taurus Mountains and Eastern Taurus Mountains, which may be related to the partial melting caused by block fracture.

The 3D shear wave velocity structure in central Turkey obtained by the modified frequency-Bessel transform method has high resolution, provide reliable data for investigation of this region, and have important guiding significance for further understanding the tectonic movement and evolution process in this region.

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