微动中多模式瑞雷波频散曲线映射式提取方法研究

The desire for a green exploration technique applicable to areas where conventional seismic methods are difficult or impossible to implement, such as densely populated urban or environmentally sensitive areas, has given rise to development of a method different from conventional seismic methods: the 'Microtremor Survey Method' (MSM). MSM is an inexpensive geophysical testing method that do not require drilling. The Rayleigh surface wave is regarded as a major source of information in the MSM. The fundamental mode and higher modes of Rayleigh waves are concomitant in microtremor and energy of the higher modes are higher than energy of the fundamental mode. But we usually analyzed microtremor using a fundamental mode only. Since it is known that the analysis considering higher modes can be consistent with the dispersion curve, we could not explain the dispersion curve only considering fundamental mode of surface waves. It is important to establish microtremor analysis method by considering higher modes. Though recent studies show higher modes of Rayleigh waves begin to be considered in MSM, the proposed methods have to depend on the geological model. In order to overcome this difficulty, we propose to start with the measured microtremor data, extract correlation coefficient curves of the multiple arrays by correlation method, establish the mapping model from correlation coefficient curves of the multi-array to dispersion curves of the multi-mode Rayleigh wave, optimize the mapping model by zonal fitting criteria and achieve the multi-mode Rayleigh wave dispersion curves directly from the measured microtremor data. We aim to give full play to the advantages of the higher modes of Rayleigh wave with more information of deep underground and greater sensitivity to stratum parameter changing, which can provide technical support for the joint inversion of geological structure to improve the retrieval accuracy and stability, as well as provide a reliable scientific basis for the application of MSM in cavity detection, active fault detection and earthquake disaster monitoring.

微动勘探技术无需激震、环保、节能, 特别适用于地下有空洞等不良地质环境和人口密集的城镇区，"绿色"的微动勘探技术正成为地质复杂环境勘查和监测的迫切选择。本项目针对现有微动中提取基阶模式瑞雷波频散曲线技术忽视高模式瑞雷波的不足和提取高模式瑞雷波频散曲线技术依赖地质模型的缺陷，从实测信号入手，通过相关法提取多台阵的相关系数曲线，建立从多台阵相关系数曲线到多模式瑞雷波频散曲线的映射模型，采用分区拟合准则优化实现模型结构，达到直接从微动信号中提取多模式瑞雷波频散曲线的目的。本项目旨在充分发挥高阶模式瑞雷波能够反映更深的地下信息、对地层参数变化敏感性更强的优势，为提高反演精度和稳定性而开展基阶和高阶模式瑞雷波联合反演地质构造的研究提供技术支撑，同时为利用微动勘探技术进行地下空洞探测、活动断裂探测和地质灾害监测等应用研究提供可靠科学依据。

在微动勘探技术应用中，若地下有低速或高速夹层，可能会出现两个或多个导波模式的瑞雷波，如果忽略高阶模式的瑞雷波，将直接影响微动勘探的实际应用；此外，高阶模式瑞雷波有时携带了更多关于地层介质的信息，特别是在低速层存在时，高阶模式相对于基阶模式瑞雷波在高频带具有更高的能量，具有更大的穿透深度，因此高阶模式瑞雷波能够在某些基阶模式失效的情况下仍然发挥作用；另外，高阶模式瑞雷波对地层参数变化的敏感性较基阶模式瑞雷波更强，因此在反演中同时考虑基阶模式和高阶模式瑞雷波的频散曲线，反演结果更为精确。签于此，本项目以提取微动中多模式瑞雷波的频散曲线为目标，系统地研究了多模式瑞雷波频散曲线提取方法及优化实现技术。在多模式瑞雷波频散曲线提取方法的建模、映射模型的优化实现等方面有新的进展和突破。本项目系统构建了提取多模式瑞雷波频散曲线的映射模型，开辟了现有基阶模式瑞雷波频散特征的研究理论延拓至高阶模式瑞雷波频散特征的理论发展方向；深入研究了提取多模式瑞雷波频散曲线的映射模型特征，创新地提出了基于分区拟合准则的优化实现技术。本项目的研究成果不仅可为多模式瑞雷波频散曲线联合反演技术的研究提供技术支撑，同时也将为微动技术在被动源勘探领域的广泛应用起到很大的推动作用，本项目的研究具有重要的理论意义和实际应用价值。