Enhancing Interpretation of Ultra-High-Frequency Offshore Seismic Data Using Adaptive Diffraction Analysis and Multipath Summation

Ultra-High-Frequency (UHF) or Ultra-High-Resolution (UHR) seismic data can image in detail several meters below the seafloor, especially in shallow waters, where the assessment of the subsurface is critical for future nearshore construction. The method can detect the subsurface structure in detail in UHF seismic records, which are characterized by a high amount of diffracted energy. With the aim of enhancing the lateral continuity and resolution for the reflectors, we applied a multipath summation approach for the first time at such high frequencies. We employed strategies for separating the diffractions from the total signal in order to clearly take advantage of their AI-located apices for further velocity analysis. The derived Root Mean Square (RMS) velocity models did not prove to be sufficient for direct migration, something that the multipath summation using 2D stacking weights sufficiently solved. We combined the focused-energy seismic sections with the derived interval-velocity models and took into consideration the available borehole data to interpret the subsurface structure. We observed a sufficient enhancement of the P-wave refraction velocity models commonly derived in such investigations. This enhancement involved not only the resolution but also the additional indications of velocity reversals, which can be a severe drawback for the stability of offshore infrastructure due to the possibility of their hazardous origin, such as fractures, unstable bedrock, or voids.