Imaging Subsurface Objects by Seismic P-Wave Tomography - Numerical and Experimental Validations

Among the many difficulties encountered in the environmental and civil-engineering fields, characterizing the subsurface from a structural and a mechanical point of view constitutes the major challenge. Seismic sounding is an appropriate geophysical method to tackle this problem because of its ability to produce high-resolution images of the first hundred meters depth. Numerous examples illustrate the diverse applications where seismic methods are effective, whether for detecting cavities, imaging active faults or delineating aquifer structure. Such seismic images are generally hard to obtain, especially when the subsurface is characterized by strong velocity variations with heterogeneities similar to the seismic signal wavelength. Subsurface imaging needs to tackle the complex problem of tomography and migration. Here, we opted for a strategy where tomography and migration processes are carried out separately. This two-step approach, taken as the basics of seismic imagery, can be carried out sequentially providing that the incident and diffracted wave fields can be separated in the data space. The proposed imaging technique is tested both for a synthetic case and a real example, for studying its robustness as well as the possible associated difficulties.