Imaging of subsurface objects using resonant seismic emission

Shallow subsurface objects with strong contrasts (such as tunnels, caves, pipes, filled pits etc) are capable of generating strong primary scattered waves, which are customly recognized as a main information carrying signals. However, detection and interpretation of those signals are heavily compromised by strong interfering noise coming from direct waves, groundroll and scattering from other subsurface heterogeneities. If our objects of interest are capable to carry waves with velocities which are slower than in the embedding medium the seismic energy can be trapped in forms of circumferential waves and than can be slowly released long after the initial impact. Release of trapped energy mostly happens as a resonant emission of shear waves and can be detected in forms of sharp resonant peaks at single records. Resonant emissions have characteristic quasi-hyperbolic traveltime patterns on single shot gathers. Inversion of these patterns allows accurate imaging of object locations, while values of resonant frequencies have direct relationship with object sizes. Imaging can be done at single frequency when no accurate information about source initiation time is needed and strong direct and primary scattering waves are simply muted. All the conclusions are supported by the results of modeling and field data.