Summary

We assess the feasibility of using Sub-Basaltic arrivals due to local Conversions (SBCs) to image structure beneath high-velocity basalt with both synthetic and real data. Detailed numerical modelling shows that in areas with water depths up to 1400m, for a 200m-thick basalt buried about 1km below the sea bed, a two-boat acquisition geometry with oset up to 12km may be used for optimum imaging based on the SBCs. Real data processing of a test line from the North Atlantic Margin reveals that the PP event from the top of the basalt, the PP and the SBC events from the bottom of the basalt form a triplet on the contour velocity spectrum. This feature can help in velocity analy-sis for SBC arrivals. Both the bottom of the basalt and the basement can be identied more condently in the nal stacking results based on the SBCs, and the thickness of the basalt is determined to be approx 200m. The processing of the SBCs also conrms the presence of sediments beneath the basalt