Preliminary Results from Marine Seismic Survey GA302 over Capel and Faust Basins

Data from 50 sonobuoys were recorded over the Capel and Faust Basins, 800 km to the east of Australia in water depths 1500-2000 m, during a 2006/07 seismic survey (GA302) for Geoscience Australia's New Oil initiative. These data were interpreted and forward modelled by ray-tracing to provide an estimate of P-wave velocities in the upper sedimentary section, and hence constrain estimates of sediment thickness. Also recorded were gravity and magnetic anomaly data which, in conjunction with the very high quality seismic reflection data, provided additional constraints upon the velocity models. The preliminary seismic reflection records studied are typified by four sets of reflection patterns: I) a ~500m thick sequence just below sea floor, II) a highly reflective flat-lying set of reflectors of variable thickness lying unconformably over III) a discontinuous, dipping, deformed sequence penetrated by high-amplitude events, and IV) deepest sequence generally marked by onset of high amplitude events. Typical ranges in four model layers below water were: 1.9, 2.3-3.0, 3.6-4.7, 5-5.3 km/s. Gravity models based on these results were compared to features identified on depth converted seismic reflection lines and indicate that sediment thickness at densities approximating 2.3 t/m3 (typically including sequences I-III) may reach 5 km in several localities.