The idea to exploit the dispersive mechanism of surface waves as a probing tool for investigating
subsurface structure was introduced about 30 years ago, and afterwards a very intense research field
has developed. Currently many methods known generally as Surface Wave Methods exist, and are well
established, most of them assuming layered or depth dependent ground models. In most cases the
parallel layer assumption is correct because the soil structure is expected to negligibly depart from a
layered structure at a typical surface testing scale for engineering and geotechnical purposes however to
exploit the amount of information achievable, it is necessary to extend the research, relaxing at least
one of the underlying model assumptions.
Indeed in classical SWM’s, surface waves are assumed to be Rayleigh waves, this means that a parallel
layered model has been implicitly assumed. As a consequence search for a soil model geometry other
than the assumed one can only result in slight perturbations. The only possible deduction is that
overcoming limitations of layered models requires to exploit P and S waves which are indeed general
solutions of the elastodynamic problem. Geometry can then be retrived by a complete waveform
inversion based on a forward model capable of successfully reproducing all of the features of the
displacement field in presence of complex scattering phenomena. In this research effort an inversion
approach has been introduced which exploits the
Boundary Element Method as forward model. Such approach is appealing from a theoretical point of
view and is computationally efficient. Although in the present work a monochromatic signal traveling
in a system constituted by a layer over an half space was investigated, this method is suitable for any
number of layers, and multi-frequency environments. The boundary element approach can be easily
generalized to three-dimensional modeling; moreover viscoelasticity can be introduced by the elasticviscoelastic
principle of correspondence. Finally BEM can be easily implemented for parallel
computing architecture. Synthetic cases of high and low impedance Jump were investigated for typical
SWM setups and a first example of application on real data was performed. Finally an elegant analytic
form of the minimization flow named Adjoint Active Surfaces was obtained combining Computer
Vision technique of Active surfaces and the Adjoint Field method