Alternative stacking techniques for deep crustal data

Abstract

Two of the distinct characteristics of the deep seismic reflection profiles from the Precambrian Arunta Block, Central Australia include the high frequency content (up to 60 Hz) of the reflections at two-way travel times of 6?10 s and the arrival of reflected energy to at least 14 s two-way time with the absence of a 'non-reflective' upper crustal zone. The data quality is generally good, though individual reflections are short in horizontal extent. Typically reflector segments are continuous over 10?30 traces which makes correlation difficult. Different stacking techniques have been used to try to increase the distance range over which correlations can be made, but with limited success over a CMP stack. The relatively high level of reflected energy from considerable depth suggested the development of an energy stack. The method is similar to 'reflection strength displays', but instead of modulating a stack with the envelope of the energy density, the energy within a specified time gate is displayed. The energy stack should be applied after equalizing the effective size of each shot to reduce contamination by near surface effects. This approach has a number of advantages: (a) the interpreter can start to look at packets of energy rather than the normal amplitude display, and the display is not affected by signal polarity; (b) the display enhances deeper events by making them stand out more clearly from a noisy background; (c) the energy display enables an easier correlation of events over greater distances. The events seen can still be discerned on conventional sections, but their clarity can be markedly improved.