Surface‐Wave Retrieval from Generalized Diffuse Fields in 2D Synthetic Models of Alluvial Valleys

Abstract

Abstract Among other methods, passive imaging technique is widely applied to obtain surface‐wave velocities. This technique implies that the average cross correlations between diffuse wavefields recorded at two observers is proportional to the imaginary part of the Green’s function. For this purpose, most applications rely on both seismic ambient noise and the coda of earthquakes. Instead, we use a generalized diffuse field (GDF), defined as the waves produced by a multiplicity of distant seismic sources. These wavefields undergo multiple scatterings along their way and at the local surface geology. In this communication, we use GDF to extract the locally generated surface waves in a 2D alluvial valley model for both inplane and antiplane cases from the retrieved Green’s function. For the inplane case, an equipartitioned cocktail of plane P , SV , and Rayleigh waves is used, whereas for the antiplane case, the incidence is a set of plane SH waves. In addition to isotropic illumination, we explore the partial illumination from one side of the valley. In both cases, we obtain dispersion curves for the Rayleigh and Love waves’ group velocities from the retrieved Green’s functions and found good agreement with the exact result for the fundamental modes of both Love and Rayleigh waves in an infinite horizontal layer. This theoretical validation is a proof of concept within an ongoing project whose goal is to improve the characterization of Mexico City subsoil throughout tomography maps of surface‐wave velocities using a collection of historical strong earthquakes recorded by the Mexico City Accelerometric Network.