浅地表主动源三维多道面波旅行时层析成像方法研究

Shear-wave （S-wave） velocity has gained popularity in environmental and engineering investigation, since it corresponds to the N-value, an index value of formation hardness used in soil mechanics and foundation engineering. Traditionally, S-wave velocity is usually derived from inverting the dispersive phase velocity of the surface wave. The Multi-channel Analysis of Surface Wave (MASW) method is the most effective method in obtaining the surface-wave dispersion curve in near-surface structures. Finely imaging the complex S-wave structure of near-surface by the MASW method, however, is limited because of the following two reasons. First, at present, the analytical solution of surface-waves dispersion can be only calculated for horizontally layered earth model. Second, the MASW method typically requires long receiver spread in order to have enough depth coverage. Hence the accuracy and lateral resolution of 2D S-wave velocity imaging by MASW method is questionable. To improve the resolution of the MASW method, this proposal is about to study the propagation process and character of surface waves in 3D complex earth model by numerical simulation method. Meanwhile, this proposal is about to study the improvements of the MASW method with inducing the surface-wave travel-time tomography method, which is a mature method in global structures detecting. Based on this research, we are about to imaging the 3D complex S-wave structures in near-surface with high lateral resolution.

在环境与工程勘察中，横波速度是能直接指示地层岩石力学性质的重要参数。面波多道分析方法，因其无损、环境友好、低成本及能提供横波速度参数的特点，在浅地表地球物理学界和地质工程领域受到广泛关注。由于浅地表地质结构复杂，面波多道分析方法在精细刻画浅地表横波速度结构上受到了限制。主要原因为：（1）现有理论框架内，面波频散曲线仅在水平层状介质中存在解析解；（2）为提高频散曲线提取质量，多道面波方法需采用长排列方式采集数据，而致使其横向分辨能力较低。本项目拟利用数值模拟通过分析面波在三维复杂结构体中的传播过程及浅地表速度不均匀对面波频散特性的影响，研究三维多道面波方法的优化观测方式。结合区域及全球尺度构造研究中常用的面波旅行时层析成像方法，处理三维多道面波数据，研究浅地表高横向分辨率三维横波速度成像方法。

在环境与工程勘察中，横波速度是能直接指示地层岩石力学性质的重要参数。面波多道分析方法，因其无损、环境友好、低成本及能提供横波速度参数的特点，在浅地表地球物理学界和地质工程领域受到广泛关注。由于浅地表地质结构复杂，面波多道分析方法在精细刻画浅地表横波速度结构上受到了限制。本研究主要目的为改善面波成像技术在浅地表横波速度结构刻画的能力，以数值模拟手段为基础，分析浅地表复杂介质中面波传播特性，总结复杂介质对面波频散特性的影响规律，并由此探寻三维面波勘探观测系统的优化设计方案，及高横向分辨率的数据处理和成像技术。其主要成果包括：设计三维水平多层介质模型（包括速度递增型、含软夹层型、含硬夹层型），系统分析三维面波勘探中多分量面波的频散特性；设计复杂浅地表模型，分析浅地表复杂性对面波频散特性及最终成像精度的影响程度；分析多道面波方法水平分辨率的影响因素，并从观测系统设计和数据处理手段两方面入手开展高水平分辨率多道面波分析方法研究，已实现基于模式分离和互相关相移扫描的相邻道高精度频散曲线提取技术、虚源多道合成技术、共中心点互相关分析技术（CMPCC）等三种高横向分辨率多道面波分析技术。