Seismic ringing effect in the shallow subsurface

We refer to the seismic ringing effect as a dynamic response of a localized shallow heterogeneity in the ground to an incident wave field originated either from a seismic source operating at the surface or from a background noise. On the seismograms the seismic ringing wave field usually appears as a long wave train with a pronounced resonant character concentrated above the localized subsurface heterogeneity. Based on the theoretical and numeric analysis of the frequency and amplitude characteristics of the ringing signals, we suggest different mechanisms that can explain the underlying features of the effect. Quantitatively, the results of our study show an excellent agreement, with an error less than 5% between analytical, numerical models and field experiments for the invoked normal modes inside the localized subsurface heterogeneity, and at least 85% agreement between the analytical model for the flexural modes and field experiments. Potentially, the ringing effect may be exploited in shallow subsurface surveys, and structural mapping of subsurface terrain.