利用江西密集台阵研究高频噪声互相关函数中的体波与高阶面波信号

With the popularity of ambient noise applications and the development of dense arrays, the analysis and application of high-frequency (0.5 to several Hz) noise cross-correlation function (NCF) is increasingly important. Compared to the traditional low-frequency (period of a few hundred seconds to 0.5 Hz) NCF, high frequency NCF has complex signal component. We obtained high-frequency NCFs using dense arrays consisted of 178 stations in Jiangxi Province. Preliminary results indicate that there are body-wave and higher-mode surface wave signals, but their signal characteristics and causes remain unknown. This project will conduct following research based on the previous work. 1) Considering high-frequency signal feature, we will integrate sub-band cross-correlation and phase-weighted stacking to form a method for extracting high-frequency NCF signals with high signal-to-noise ratio. 2) We will integrate the array technology and the nine-component NCF to form an identification method for body waves and higher-mode surface waves. Combine large-scale, long-term data to study the propagation laws of various types of signals. 3) Based on the signal characteristics, we will use numerical simulation to analyze the generation mechanism of high-frequency NCF signals. The results of this project will contribute to signal extraction, recognition and application of high frequency NCF, as well as to furthering the understanding of various signal causes in high frequency NCF. In addition, it will be of great significance to better utilize high frequency NCF for shallow tomography.

随着噪声应用的普及和密集台阵的发展，对高频（频率0.5Hz至几Hz）噪声互相关函数（NCF）的分析和应用日益重要。相比传统的低频（周期几百秒至频率0.5Hz）NCF信号，高频NCF中信号类型复杂。我们利用由178个台站组成的江西密集台阵获取了高频NCF，初步结果表明其中存在体波和高阶面波信号，但其信号特征和成因仍需进一步研究。本项目拟基于前期工作开展如下研究：1）针对高频信号特征，整合分频窄带滤波和相位加权，形成提取高信噪比高频NCF信号的计算方法；2）综合台阵技术和九分量NCF，形成对体波及高阶面波的判别分析方法。结合大范围、长时间的数据研究各类信号的传播规律。3）基于信号特征，结合数值模拟分析高频NCF各类信号的产生机制。本项目结果有助于高频NCF中信号的提取、识别和应用，加深对高频NCF中各类信号形成机制的认识，同时对更好地利用高频NCF开展浅层成像工作具有重要意义。

震台站记录到的长时间背景噪声的互相关函数（Noise Cross-correlation Function，NCF）可以近似地表征台站间的格林函数。利用NCF对地下结构成像及波速变化监测的研究在地震学中得到了广泛的应用。NCF逐渐成为一种新型的地震观测工具，对NCF中各类信号的分析和利用，促进了噪声地震学的发展。随着密集台阵大量布设，对高频噪声互相关函数的应用普及，高频的噪声互相关函数的分析和应用日益重要，相关理论与应用成为新的研究热点。结果表明其中存在体波信号及高阶面波信号，但其信号特征和成因仍需要进一步研究。项目利用该密集台阵，开展NCF中的不同性质不同频率信号的机制研究。本研究取得如下研究成果：1）完成数据基础算法流程的构建。建立观测数据库，对数据进行整理和归档。针对不同信号特征，整合RMS筛选叠加和分频段互相关和时频加权，形成提取高信噪比形成高频NCF信号的计算方法；2）结合气枪数据和密集台站数据，获取研究区域地下精细速度结构，获取本地介质结构对信号发育影响的基础；3）综合台阵技术和九分量NCF，和不同信号叠加方法，追踪NCF信号中体波和面波信号的来源。结合大范围、长时间的数据研究各类信号的传播规律。发现体波信号主要以P、PP和PKPbc三种震相的形式存在。定位结果显示较强的体波类型噪声源主要位于海岸线和深海中，与全球海洋活动较为剧烈的区域存在较强相关性。而不同周期的体波噪声源位置略有差异。4）追踪了不同频率体波信号来源，总体而言，噪声能量在北半球冬季较强，夏季较弱。采用聚束分析，得到不同频率下NCF面波信号的来源及产生机制。