联合背景噪声自/互相关及接收函数方法研究大别地区速度结构

The Dabie Orogen forms one of the most important collisional zone between the South China Block (SCB) and the North China Block (NCB). The high precision and high resolution lithospheric seismic velocity structure in this region may provide crucial information about the collision boundary and the distribution pattern of the high pressure metamorphic (HPM) rocks. However, due to the complex collision process, the crustal and upper mantle structures are quite complicated, and the underground layers vary dramatically in this region, which cause difficulties for deciphering the velocity structure in this region. So, the spatial resolution and the precision of the present lithospheric seismic velocity structures in this region are needed to be updated. Due to the nature of the ambient noise analysis, it is free from the constraint of earthquake distribution, and the errors of source parameters, thus can provide accurate surface wave dispersion curves. Besides, the auto-correlation function of ambient noise is sensitive to the variations of underground layers. Moreover, the teleseismic receiver function can also provide critical constraints to Moho depth and Vp/Vs ratio. For this reason, joint inversion with the auto-/cross-correlation functions of ambient noise data, and teleseismic receiver functions can improve the precision of seismic velocity structures and undulation of underground layers dramatically. In this project we propose to collect the continuous seismograms from the permanent network and the 46 campaign broadband seismic stations in the Dabie Orogen zone, do a joint inversion with surface wave dispersion curves and auto-correlation functions from ambient noise, and teleseimic receiver functions to build a high spatial resolution and accurate seismic velocity structure in the Dabie Orogen, so that we can outline the distribution of the collision zone between SCB and NCB, and the distribution of HPM rocks, and further to provide scientific evidences for understanding the dynamic mechanism of the continental collision process in this region.

大别造山带是研究华南-华北碰撞、演化的关键区域。其壳幔精细速度结构对圈定块体的缝合位置、超高压变质岩分布范围具有重要意义。由于构造复杂、地下界面断错起伏、壳幔板片叠置，以往的速度结构研究在分辨率和精度上需要进一步提高。地震噪声自/互相关函数不受地震空间分布和震源误差的影响，能良好的反映地震波速度结构，且自相关函数对界面非常敏感；另外，远震接收函数能够辅助确定Moho面，对界面倾斜和Vp/Vs给出较好的约束。因此，三者的联合反演能够显著提高结果的准确性。本项目拟整合大别造山带及邻区的宽频带固定台网和46个流动台站记录，联合噪声面波频散曲线、噪声自相关函数和接收函数，反演获取高分辨率的地壳和上地幔速度结构和界面起伏，为确定该区板块碰撞边界及超高压变质岩的分布和大陆动力学提供科学参考。

大别造山带与秦岭、苏鲁造山带构成东亚最重要的碰撞带之一，受郯庐断裂平移错动切割、华北-扬子陆块碰撞以及下扬子陆块的俯冲等多源深层过程的综合作用，呈现出一系列特殊的构造特征，是研究古大陆边界以及陆陆碰撞造山过程等地球动力学和大陆岩石圈变形问题的理想场所。壳幔的速度结构记录着其动力演化过程的痕迹，且具有明确的物理含义，因而研究地下速度结构成为探索构造形成及演化的有力方法。大别造山带地区亦是如此，一直以来也备受关注。.较前人的研究成果，我们出于方法的改进和流动台站数据的优势，提出对该地区的速度结构进行研究。鉴于该地区构造复杂、地下界面断错起伏、壳幔板片叠置，本研究主要基于背景噪声互相关、自相关以及远震接收函数方法，各取其优点，以获取该地区三维高分辨率速度结构。因此，本研究主要对背景噪声自相关、互相关函数、远震接收函数进行研究计算，联合三者开展该地区的速度结构反演。.本项目在开展过程中，除了研究台站间垂直向（ZZ）互相关函数以外，还研究了垂向-径向（ZR）和径向-垂相（RZ）互相关函数提取台站间经验格林函数。后者在噪声源分布不均或者有固定噪声源的情况下，比前者信噪比更好。.在大别地区，主要加入了21个流动台站，以背景噪声面波成像展示为例，加入流动台站能够将已有的“普遍到达1°×1°、部分达到0.5°×0.5°的分辨率”提高到0.5°×0.5°甚至在密集台站地区30 km×30 km。根据结果，我们勾勒了红安-桐柏超高压变质岩的可能展布范围，探索了郯庐断裂的切割深度、浅层断裂与该地区地震活动性的关联；为确定该地区超高压变质岩的分布和大陆动力学提供科学参考，也为该地区地震的研究提供速度结构模型。本研究能提供的参考还很有限，但为后续工作积累了经验，正在对一些结果进一步完善和确认，以不断加深我们对该地区结构的理解。