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从地震背景噪声、地震波直达波或者地震波尾波的相关函数中提取近似格林函数(Estimated Green’sFunction)已经成为地震学研究的一个热点.由近似格林函数中提取面波频散曲线,进而研究地壳和上地幔结构,已经成为地震学研究地球内部结构的一种新方法,其尺度由最初的几十千米发展到全球尺度.从原理上,只要由充分漫射波场的数据计算得到的互相关函数都可以得到近似格林函数,但在地震背景噪声数据的实际处理过程中,需要通过时间域的归一化处理压制地震信号的影响,然后利用频率域归一化压制单色噪声源影响和提高信噪比.但是时间域归一化的常用方法均为非线性,影响进一步提取噪声互相关函数(NCF)中的有效信息.我们通过对比有无时间域归一化和频率域归一化对不同数据进行计算得到了相似的NCF,发现时间域归一化处理并非必需,在此基础上频率域归一化处理也可以省略,由此得到一个简化的处理流程,直接计算长时间的地震记录的互相关函数得到近似格林函数,并且最大限度保留了原始振幅信息,可以更有效地用于研究噪声源.
Estimating Green’s Function from the correlation function of seismic background noise, seismic direct wave or seismic wave coda has become a hot research topic in seismology.The surface wave dispersion curve is extracted from the approximation Green’s function, and the crust And the upper mantle structure has become a new method of seismology study of the internal structure of the earth, its scale from the initial tens of kilometers to the global scale.From the principle, as long as the data from the fully diffuse wave field calculated However, in the actual processing of seismic background noise data, the influence of seismic signal needs to be normalized in the time domain, and then the influence of the monochromatic noise source is normalized by using the frequency domain Improve the signal-to-noise ratio, but the commonly used methods in the time domain are non-linear and affect the further extraction of the effective information in the noise cross-correlation function (NCF) .We compare whether the time domain normalization and the frequency domain normalization The calculation of different data obtained a similar NCF, found that the time domain normalization is not necessary, on the basis of the frequency domain normalized Process may be omitted, thereby to obtain a simplified process flow, direct calculation of the long cross-correlation function of the seismic records obtained approximate Green’s function, and to maximize the retention of the original amplitude information, can be more effectively used to study the noise source.