Data from a dense array of OBS used in the survey of a volcanic continental margin have been used successfully to image sub-basalt crustal structure using a robust tomographic inversion technique. The acquisition of wide-angle data using a low-frequency source allows useful data to be collected in regions where extruded basalts typically hinder conventional seismic imaging; OBS data can provide accurate seismic velocities at depth, therefore improving seismic imaging and interpretation of lithology, as well as providing important crustal structure information.