Surface waves back-scattering analysis of subsurface heterogeneities.

The existence of heterogeneities within the near sub-surface becomes a potential hazard in subsurface exploitation activities. Consequently, accurately identifying and characterizing these discontinuities in seismic surveys is vital for effective threat mitigation. In this regard, investigating the backscattering of surface waves generated by such obstacles emerges as a critical approach for locating and understanding these heterogeneities, thereby reducing potential risks. This thesis focuses on analysing the presence of surface cracks of different sizes within synthetic homogeneous half-space models in 2D and 3D, together with a layered half-space model in 2D. Synthetic seismic data is generated for each model by numerically simulating the wave propagation using a staggered finite differences grid, and undergoes its study together with the data generated in models without heterogeneities in time and frequency domain. Through the analysis of the back-scattering coefficient in frequency domain for the 2D models, a consistent behaviour of the phenomena is identified, and dimensionless expressions can be determined and related to other surface waves properties, which can be extrapolated to any type of crack and frequency studied. Following, an analysis of 3D models over different frameworks is performed to identify the characteristics of scattering field which can become an important factor to locate and migrate near-surface heterogeneities on real data. Between them it has been identified the directivity of the scattering field, the location of the centre of the heterogeneity or the geometrical setting effects over the wavefield.