Ocean-bottom seismograph and conventional reflection surveys in the Petrel Sub-Basin: an integrated seismic study

Abstract

The ocean-bottom seismograph (OBS) data recorded in the Petrel sub-basin with a 100 m shot interval were not spatially aliased with respect to prevailing velocities and frequencies. This enabled the utilisation of digital seismic processing techniques not normally used to process refraction and wide-angle data. F-k filtering was used to enhance signal/noise ratio at large (tens of km) offsets. Depth migration of wide-angle reflections utilised the interpretation of signal dynamics to supplement the travel times-based interpretation conventionally used for refraction and wide-angle data. The project provided valuable velocity information to better constrain the depth conversion of AGSO’s regional deep reflection profiles in the region. Prominent reflectivity seen in the conventional reflection data at two-way times (TWT) greater than 4 s does not correspond to any velocity increase imaged by refraction/wide-angle techniques. On the other hand, the most significant velocity increase, which occurs at the Moho, does not produce high-amplitude near-vertical reflections. Interval velocities estimated from the conventional reflection data at TWT greater than 2 sec appear to be up to 1 km/s lower than those derived from the OBS data. If the former are used to depth convert reflection data, then depth to seismic boundaries in the centre of the basin at TWT 6-9 s would be underestimated by up to 2 km. Seismic reflection and refraction techniques are complementary to each other, and both are required to fully interpret the data.