背景噪声互相关函数多尺度成像研究

当前研究表明噪声互相关函数中成分较为复杂，其包含各阶频散曲线信息，传统从互相关函数中提取基阶频散曲线信息成像方法存在有效信号遗漏风险.因此，本研究不再提取频散曲线，而是直接利用互相关函数进行成像，系统研究了基于两个台站的噪声互相关函数数据处理、正演和反演方法.此外，在地震勘探中，如何划分地层网格，并选择合适的反演频段对于高精度成像具有较为重要的意义.因此，本研究提出了层厚和反演深度随频率变化的多尺度反演方法.在成像中首先划分较粗的地层网格，选择较低的频段反演得到地下大尺度介质结构，由于较粗网格虽然反演稳定且计算量较小，但分辨率有限，因此对反演大尺度结果重新划分较细网格，并选择高频段进行反演，这一策略可以减少反演参数个数，从而提高反演稳定性，并且降低计算量，同时可以从模型尺度提高反演的分辨率.实际数据处理验证了方法可行性.本文噪声互相关函数成像方法为仅能布设少量地震台站的特殊地区的探测（如月球、火星等地外天体）提供了更多选择，并且为复杂介质多尺度成像方法的研发铺平了道路.

Multiscale imaging of ambient noise cross correlation function

The current research shows that the composition of the cross-correlation function (CCF) is relative complex, which contains the dispersion information from the multimodal surface waves, not only the fundamental-mode. The traditional imaging method of extracting fundamental-mode dispersion curve from the CCF has the risk of missing effective signals. Here, we proposed an imaging method only by using the CCF other than extracting information from the dispersion curve. Data-processing, forward modeling and inversion methods about the CCF are also studied in this research. In seismic exploration study, how to divide the stratigraphic grid and select the appropriate inversion frequency band is of great significance for high-precision imaging. This study proposed a new multi-scale inversion method, In this method, the layer thickness and inversion depth can be varied with different frequencies. Firstly, the coarser stratigraphic grids are divided, and the lower frequency-band information is selected to invert to obtain the underground large-scale medium structure. This coarser grid division makes the inversion stable and requires less computation, but the resolution is limited, so the large-scale inversion result is re-divided into finer grids, and the higher frequency-band information is selected for inversion. This method can reduce the number of inversion parameters, improve the stability of inversion, reduce the computation cost, and ensure the model-resolution of the inversion result at the same time. Subsequently, the analysis of the field data verifies the feasibility of the proposed method. This noise cross-correlation function imaging method provides more options for the exploration of special areas where only few seismic stations can be deployed (such as the Moon, Mars and other extraterrestrial celestial bodies), and paves the way for the development of muti-scale imaging methods for complex media.