A new high-precision velocity model building technique to marine data in strike-slip structural zones

The shallow water OBN survey area A, located in the Southern Caspian Sea, lies within a strike-slip fault zone. For the legacy data, the traditional time-domain root mean square (RMS) velocity was converted to depth-domain interval velocity for initial velocity model building, followed by reflection tomography to update the velocity model. However, this approach failed to meet the high-precision velocity model building and imaging requirements for this region. Considering the seismic data characteristics of the area, four innovative integrated techniques were applied to achieve high-precision velocity model building and depth migration imaging. These techniques include: (i)near-seabed velocity model building, (ii) structure-guided, well-controlled velocity model building, (iii) full waveform inversion, and (iv)tilted transverse isotropy (TTI)multi-azimuth grid tomography. The approach initially involved building a high-precision near-seabed velocity model by combining a first-break tomography velocity model with the corresponding high-velocity layer (HVL). A comprehensive velocity model for the mid-to-deep subsurface layers was developed by integrating well logs, geological horizons, and time-domain RMS velocity. The initial velocity model was then optimized using full waveform inversion (FWI). Finally, TTI multi-azimuth grid tomography was applied to address anisotropy in the subsurface media caused by the development of faults and fractures in the area. By combining these four advanced techniques, migration results of higher quality than the legacy data were achieved. The continuity and energy of events on the PSDM section improved significantly. The faults became clearer, and structural interpretation was more accurate. The migration result better satisfied the requirements for high-precision velocity model building and depth migration imaging in this region, providing higher-quality seismic imaging data for interpretation. The innovative integrated techniques proposed in this paper provide valuable references for seismic data processing in similar regions.