Preliminary deep reflection studies in the Arunta Block, Central Australia

Abstract

Summary. In 1985, near-vertical incidence reflection profiling was carried out across the Arunta Block in Central Australia. This region consists of exposed Proterozoic metasediments, granites and granulites. There is usually a limited sedimentary coverage generated by deep weathering. The seismic sections for the deep crust are markedly different from those previously recorded in Eastern Australia where there is extensive sedimentary cover. One of the striking features is the presence of energy with frequencies as high as 100 Hz at two-way times of 5-6 s. Reflections are found throughout the crust, and there is no zone that can be characterised as non-reflective. The strongest reflectors commonly lie in the intervals around 4-6 s and 8-11 s and display significant dip. Individual shot records show fairly rapid variations in amplitude and waveform within a reflection band and the correlation between records from adjacent shots can also be somewhat limited. Such features are not well suited to the application of standard processing techniques designed for subhorizontal structures, and call into question the utility of conventional stacking. The character of the reflections changes markedly with varying frequency which suggests that they arise by interference phenomena, probably associated with laterally varying lamellar structures.