Abstract

It has been recently demonstrated that averaging the autocorrelations of fields produced by various almost‐vertical incoming elastic body plane waves upon a layered system approximately leads to the imaginary part of the corresponding 1D Green’s functions for deep sources located underneath the receiver (Kawase et al., 2011). Thus, the ensemble of these waves from deep earthquakes recorded in a station located in the epicentral zone is interpreted as a diffuse field. In this short note, we extend the study to consider earthquakes recorded in a station located at epicentral distances of up to hundreds of kilometers. We consider the horizontal‐to‐vertical spectral ratio (HVSR) of the averaged P, S, and coda waves and full earthquake records at the Cibeles station (Mexico City Accelerometric Network) and compare these with the results obtained with the corresponding HVSR for the 1D (Kawase et al., 2011) and the 3D (Sánchez‐Sesma, Rodríguez, et al., 2011) diffuse fields models. Using the signals of 90 earthquakes recorded at Cibeles, we find that the experimental results have distinctive features compatible with the 3D signature of a diffuse field. We interpret this result as a consequence of the multiple paths that seismic waves undergo from the subducting slab to the Mexico City valley and to the multiple scattering in a complex tectonic environment. Our study strongly suggests that we can use strong‐motion records from earthquakes and apply similar techniques to the ones used to analyze the ambient seismic field.

Online Material: Earthquake catalog.

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