Updated: Apr 30, 2021

IGCP Project 559 – Historic Data – Mapping the Moho using deep reflection profiling techniques, Mildura, Australia, 1968.

Information compiled by D. M. Finlayson (doug.finlayson@netspeed.com.au)

During the 1960's techniques for deep seismic profiling of the deep crust were still being developed. The techniques used for oil exploration of the sedimentary layers at depths down to about 5-6 km were being tried to image the deeper crust to depths of about 30-35 km.

In Australia, tests were conducted by the Australian Bureau of Mineral Resources, Geology and Geophysics (BMR) in 1968 near Mildura in western New South Wales to test equipment configurations for imaging the deep crust. These tests included experimenting with geophone spreads, and types and depths of explosive charges drilled into the ground and signal filters. In Europe and North America similar experimentation was being conducted.

The experimental work at Mildura within the flat-lying Murray Basin was spectacularly successful with clear seismic reflection images of the Moho being obtained. The figure (see image) shows an image with strong energy being reflected at near-vertical incidence with two-way reflection times (TWT) of 9.5-10.5 seconds. This is equivalent to a Moho depth of about 29-31 km. Final published value - 30.6 km.

The seismic geophone array and shot configuration was as follows:

• Geophones - HSJ 14Hz
• Magnetic tape recorder - DS7-700, 24 channels
• Amplifiers - TI-8000
• Geophone pattern - 16 geophones, 6 m apart in-line
• Station interval 90 m
• Seismic geophone spread configuration for continuous profiling - 1080-0-1080 m
• Shot hole depth - 36 m
• Charge size - 23 kg/hole, 5 holes/shot

The deep seismic profiling conducted at Mildura was part of a program conducted by BMR at many sites around Australia in the 1960's to optimise the techniques for imaging the deep crust beneath the sedimentary layers. At that time BMR operated two seismic profiling crews to investigate the oil and gas potential of Australia's onshore sedimentary basins.

Bibliography

Branson, J. C., Moss, F. J., & Taylor, F. J., 1976. Deep crustal reflection seismic test survey, Mildura, Victoria and Broken Hill, NSW, 1968. Bureau of Mineral Resources, Geology and Geophysics, Report 183, pp 30.

Dooley, J. C., & Moss, F. J., 1988. Deep crustal reflections in Australia 1957-1973 - II. Crustal models. Geophysical Journal, 93, 239-249.

Moss, F. J., & Dooley, J. C., 1988. Deep crustal reflection recordings in Australia 1957-1973 - I. Data acquisition and presentation. Geophysical Journal, 93, 229-237.