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THE APPLICATION OF SEISMIC WIDE-ANGLE REFLECTION TECH- NIQUES TO THE EXPLORATION FOR UNDERGROUND WATER

L.V. HAWKINS

School of Applied Geology, University of New South Wales, Kensington, N.S. W. (Australra)

Geophysical investigations for underground water in deep alluvial filled valleys commonly employ seismic refraction and electrical resistivity methods with empirical control and supplementry well logging data obtained from drilling.

The thickness of alluvial fill in such valleys may be up to some 200 m with considerable complexity in the seismic velocity structure in the silts, sands and gravels, saturated and unsaturated, in the alluvium. This is frequently further complicated by underlying weathered and unweathered bedrock of medium velocity and higher velocity older basement rocks below.

Such layered geological sections raise difficulties in the application of the seismic refraction method because of velocity inversion and blindzone (masking) problems inherent in the refraction method.

It is proposed that the application of shallow seismic reflection spreads to obtain more detailed and accurate velocity information from wide-angle reflec- tion/refraction data, is a necessary development in the application of seismic methods to this problem. The interval velocity determinations, particularly from applying recording and reduction techniques similar to those developed for marine sonobuoy data, should provide a valuable additional stage in the geophysical exploration phase of these investigations prior to drilling.

REVIEW OF GEOPHYSICAL EXPLORATION AT CAPTAINS FLAT, NEW SOUTH WALES

E.C.E. SEDMIK and L. DAVIES

Bureau of Mineral Resources, Canberra, A.C.T. (Australia) Electrolytic Zinc Company of Australia, Melbourne, Vie. (Australia)

The first geophysical tests in the Captains Flat area were conducted by the Imperial Geophysical Experimental Survey during 1930. The electromagnetic method known as Bieler Watson was used and the tests were done over known lode situated between the Elliots and Keatings sections of the Lake George Mine.

Geophysical surveys employing self-potential and magnetic methods were carried out by Conaghan and Foskett from the New South Wales Department