Imaging subsurface geological structures
Application of seismic methods in coal exploration is a standard approach. However, standard seismic methods cannot image the near-surface for the majority of the cases as the reflections are degraded by the appearance of various types of noise and the earth’s excessive heterogeneity in this zone.
In the following example, a high-resolution 2D image of the earth was constructed by the interferometry of downgoing seismic waves and their multiples.
Sources are activated on the surface and the waves are recorded in a borehole by a number of geophones.
Coda Wave Interferometry
The scattered wavefield caused by a passing seismic wave (e.g. earthquakes, active seismic etc.) can vary in phase and amplitude in accordance with the change in the medium velocity. The scattered field is usually observed in the coda of a passing wave and is very sensitive to variations in shear wave velocity of the rocks. The high sensitivity of the scattered wavefield to small variations in shear wave velocity can be used to detect points of lost shear strength in rocks such as leak zones in TSF structures or damaged roofs and walls in open pit and underground mines.