Downward Continuation of Wide-Angle Seismic data: implications for traveltime tomography uncertainty

Controlled-source marine seismic experiments are key in advancing our understanding of the Earth’s subsurface structure to study tectonic, magmatic, sedimentary and fluid flow processes. Joint acquisition of Wide-Angle Seismic (WAS) and Multi-Channel Seismic (MCS) streamer data stands as the most robust approach for marine exploration, however effectively mapping subsurface structure remains challenging. The lack of identifiable refractions as first arrivals at short offsets inWAS data leads to illumination gaps of the upper 2-4 km of the subsurface structure at 8-12 km offsets around Ocean Bottom Seismometers (OBS). This inadequate ray coverage at the shallow subsurface limits the performance of Travel Time Tomography (TTT) techniques and affects velocity determination in the sedimentary layer and reflector location, propagating errors to deeper layers. This study integrates Downward Continuation (DC) to WAS data. Similarly to DC applied to MCS data, redatuming WAS data involves using the acoustic wave equation backward in time. This process virtually repositions the sources to the seafloor, revealing previously masked near-seafloor refractions as first arrivals. This transformation significantly enhances ray coverage in the shallow subsurface, leading to more accurate determinations of both seismic velocity and reflector geometry. By bridging theoretical concepts with a real data application, this study demonstrates the optimization of field seismic data for improved TTT results. This methodology is particularly beneficial for deep water exploration where spatially coincident WAS and MCS are jointly inverted. In such scenarios, DC-processed WAS data provides the refracted phases key for velocity determinations, and that are typically not present in MCS data due to insufficient streamer length relative to the water column depth. Additionally, we contribute to the community by releasing our open-source, High-Performance Computing (HPC) software for WAS data redatuming.