Ambient seismic noise (ASN) is becoming of interest for geophysical exploration and engineering seismology, because it is possible to exploit its potential for imaging. Theory asserts that the Green’s function can be retrieved from correlations within a diffuse field. Surface waves are the most conspicuous part of Green’s function in layered media. Thus, the velocities of surface waves can be obtained from ASN if the wavefield is diffuse. There is widespread interest in the conditions of emergence and properties of diffuse fields. In the applications, useful approximations of the Green’s function can be obtained from cross correlations of recorded motions of ASN. An elastic field is diffuse if the background illumination is azimuthally uniform and equipartitioned. It happens with the coda waves in earthquakes and has been verified in carefully planned experiments. For one of these data sets, the 1999 Chilpancingo (Mexico) experiment, there are some records of earthquake pre‐events that undoubtedly are composed of ASN, so that the processing for coda can be tested on them. We decompose the ASN energies and study their equilibration. The scheme is inspired by the original experiment and uses the ASN recorded in an L‐shaped array that allows the computation of spatial derivatives. It requires care in establishing the appropriate ranges for measuring parameters. In this search for robust indicators of diffusivity, we are led to establish that under certain circumstances, the S and P energy equilibration is a process that anticipates the diffusion regime (not necessarily isotropy), which justifies the use of horizontal‐to‐vertical spectral ratio in the context of diffuse‐field theory.

中文翻译：

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环境地震噪声扩散特性的探索

环境地震噪声 (ASN) 正变得越来越受地球物理勘探和工程地震学的关注，因为它可以利用其成像潜力。理论断言格林函数可以从扩散场内的相关性中检索出来。面波是层状介质中格林函数最显着的部分。因此，如果波场是扩散的，则可以从 ASN 获得表面波的速度。人们对漫射场的出现条件和特性有着广泛的兴趣。在应用中，可以从记录的 ASN 运动的互相关中获得格林函数的有用近似值。如果背景照明在方位角上均匀且均分，则弹性场是漫射的。它发生在地震中的尾波中，并已在精心策划的实验中得到验证。对于这些数据集之一，1999 年 Chilpancingo（墨西哥）实验，有一些地震前事件的记录无疑是由 ASN 组成的，因此可以对尾声的处理进行测试。我们分解 ASN 能量并研究它们的平衡。该方案受到原始实验的启发，并使用记录在 L 形阵列中的 ASN，允许计算空间导数。在为测量参数建立适当的范围时需要小心。在寻找鲁棒的扩散指标时，我们被确定为在某些情况下，S和P能量平衡是一个预测扩散状态（不一定是各向同性）的过程，