High-resolution seismic imagery of palaeochannels near West Wyalong, New South Wales

Abstract

Two high-resolution 2-D seismic surveys were carried out over palaeochannels near West Wyalong, NSW using an IVITM mini-vibrator. The first aim of these seismic surveys was to map in detail the profile of the palaeochannels. The second aim was to establish the regolith stratigraphy within the channels and evaluate the techniques used for acquiring and processing such data. Short receiver spacings, down to one metre, were used in order to achieve satisfactory resolution of the anticipated shallow targets. The short length of the split spread meant that extra effort was required to eliminate noise close to the source. Paradigm Inc. DISCOTM/Focus software allowed interactive tests of processing parameters. A combination of bandpass filtering, spectral equalisation, mutes, and f-k filtering proved effective in suppressing noise and enhancing reflections on the shot records. Refraction statics have been calculated from the first arrivals for all the shots for both lines to reveal the shape of the uppermost layers. Examples of processing tests, as well as the interpreted seismic sections, are presented to demonstrate the effectiveness of high-resolution seismic techniques in imaging regolith stratigraphy and buried palaeochannels. Preliminary results, when tied to borehole data, indicate possible palaeo-erosion surfaces and maghemite gravel-filled palaeochannels to 10 m depth. Saprolite and bedrock interfaces are apparent, indicating palaeotopography with relief exceeding 100 m.