Lessons learned from marine refraction seismic experiments in the Ligurian Sea

Wide-angle refraction seismic experiments are generally executed along 2D profiles. In this study, we investigate the potential and limitations of using adjacent 2D wide-angle seismic profiles for 3D tomography. From this, we provide suggestions on best practices when designing new offshore experiments so that the data can be used for both 2D and 3D tomography. We use two example experiments from the Ligurian Sea, the 2006 SARDINIA Experiment and the 2017/8 AlpArray—LOBSTER Experiment, to highlight the benefits and pitfalls of two common station-shot geometries: parallel 2D seismic profiles and crossing seismic profiles through a network of Ocean Bottom Seismometers (OBS). We interpolate the lateral resolution of these experiments, and compare this with the potential resolution that could be achieved by the strategic addition of shots or stations. The synthetic results show that when two parallel 2D seismic profiles are shot (Sardinia Experiment), the resolution can be equally improved by the addition of a line of shots between profiles as by a line of stations between profiles. For an OBS network (AlpArray—LOBSTER Experiment), the synthetic results show that additional shot lines throughout the network are necessary to resolve the network area. One major difficulty with this specific area, is the complex geological structure of the Liguro-Provençal Basin, especially the presence of a Messinian evaporite layer that interferes with and scatters the seismic signal. The resolution achieved by these different network geometries shows that while these experiments alone were not sufficient for 3D tomography, they could both have been made suitable for 3D tomography by the addition of shot profiles, which are cost-effective and easier to add than stations. This workflow for estimating the lateral resolution of a 3D seismic refraction experiment can be applied to any tectonic setting, and should be considered when planning offshore experiments to enable 2D and 3D tomography and increase the output of this valuable data.