3D Ultra-High-Resolution Depth Velocity Model Building and Full Waveform Inversion for Offshore Wind Site Characterization

Paper submitted to NPF Biennial Geophysical Seminar 2026, by Luca Limonta, Bertrand Caselitz, Bent Erlend Kjølhamar and Roberto Ruiz (TGS)

Summary

3D Ultra-High-Resolution Seismic (3D UHRS) surveys are increasingly used for offshore wind farm site characterization, where accurate near-surface imaging is essential for foundation design and the reduction of geotechnical uncertainty. These datasets demand specialized processing workflows that extend beyond conventional time processing, critically incorporating velocity-model building (VMB) and imaging.

Traditional 2D site surveys rely on sparse lines and time-domain velocity analysis to flatten CMP gathers, producing RMS velocities that don’t measure accurately soil variations. To advance beyond this limitation, we applied a full 3D depth-domain VMB workflow combining Kirchhoff PreStack Depth Migration (KPSDM), 3D tomography, and Dynamic Matching Full Waveform Inversion (FWI) (Huang et al., 2023) up to 600 Hz to resolve sub-10 m wide geologic features in unconsolidated sediments.