Seismic refraction investigations were made at five sites in the vicinity of Alice Springs, Northern Territory, by the Bureau of Mineral Resources in August 1962. This work was done, at the request of the Bureau of Mineral Resources Observatory Group, to select the most suitable site for a seismological observatory. In view of the desirable features for such a site - a bedrock having a high seismic velocity and a bedrock at shallow depth - a site about three miles west of Alice Springs is recommended as the most suitable; the bedrock material has a velocity of 17,800 ft/s and the thickness of overburden is less than 20 ft.

Presentation delivered at the Tasman Frontier Workshop, 89- March 2012

The geophysical survey described in this report was undertaken at the request of the Snowy Mountains Authority for the purpose of investigating possible sites for the proposed Spencer's Creek dam. The area surveyed is about two miles above the junction of Spencer's Creek with the Snowy River, about six miles east of the summit of Mt. Kosciuszko, and at an average elevation of about 5,700 feet above sea level. The specific information sought by the survey comprised the following: depth and nature of the bedrock, contours of the bedrock surface, nature of the overburden, and in particular, variations in physical properties occurring either horizontally or vertically. The seismic refraction method was used in the survey. This report gives an account of the geophysical survey and its results.

At the request of the Australian Atomic Energy Commission, the Bureau of Mineral Resources, Geology & Geophysics conducted a seismic refraction survey on the site chosen for construction of a nuclear power station. The purpose of the survey was to determine the foundation conditions at the site and the properties of the rocks in relation to excavation methods and support of the proposed structures. The bedrock of the area consists of Permian sandstone (Jervis Bay Sandstone) overlain in places by unconsolidated Quaternary beach and dune sands. During the seismic work it was found that the sandstone beds have a relatively wide range of seismic velocities; often a higher-velocity bed overlies a lower-velocity bed, and this makes seismic refraction work difficult and less accurate. This is confirmed by laboratory measurements of seismic velocities on drill cores. Thin beds of higher- and lower-velocity sandstones occur, some too thin to be resolved by the seismic method. The seismic profiles presented must be considered bearing in mind these difficulties, Haterial sufficiently consolidated for foundations is shallow, and the seismic velocities indicate that some blasting will be necessary to excavate to the desired depth of 10 feet above mean high water level.

An experimental seismic survey using both refraction and reflection techniques was carried out in April, 1958, near Morwell in the Latrobe Valley at the request of the State Electricity Commission of Victoria. The object of the survey was to find if the method was of value in mapping the structure of the coal measures of the Latrobe Valley and in providing information on the depth to and type of basement underlying the coal measures. Work was concentrated in an area south-west of Morwell on the southern limb of the Latrobe Syncline. The results obtained indicate that the seismic method may be applied successfully to geological problems of the Latrobe Valley and may provide useful control data for the interpretation of surface geological and gravity mapping. Various interpretations of the results are discussed and although some ambiguity exists, it might be overcome when more work is done, particularly if an accurate knowledge of the velocities of the coal easures is obtained. It has been possible by means of refraction work to map the extension of the basalt which crops out on the southern margin of the Latrobe Syncline beneath the coal measures with reasonable certainty.

A seismic reconnaissance, traverse was surveyed for 20 miles along an east-west line,. 10 miles 'north of -Carnarvon, as part of a regional investigation of the southern part of the Carnarvon Basin, W.A. Both reflection and refraction techniques were used, and the results were Correlated, where possible, with the known formations in the Pelican Hill bore. Several reflecting horizons could be followed although reflections from below the level of the Cretaceous/Palaeozoic unconformity were badly interfered by multiples. The refraction method was successful, and recorded three main refractors with velocities of 14750.ft/sec, 18400 ft/sec, and 20,280 ft/sec. The main feature of the section obtained is a broad antiform within the Palaeozoic sediments, shown particularly by the 20 2 280 ft/sec refractor, which is_a good marker. for structural mapping. This marker has been tentatively correlated with the Dirk Hartog Dolomite, which would suggest that the strata underlying the Gneudna Formation in the Pelican Hill bore belong to the Nanyarra Greywacke rather than the Tumblagooda Sandstone. Overall the profile of the 20 2 280 ft/sec marker has a slight west dip from about 4000 feet at the eastern end to about 5000 feet at the western end of the traverse. The Cretaceous/Palaeozoic unconformity was fairly flat at a depth of about 1500 feet. Indications from the reflection cross-section and from the profile of the 18,400.ft/sec refractor are that the sediments between the two above horizons are similar in structural attitude to the deeper horizon.

Various aspects of isostasy concept are intimately linked to estimation of the elastic thickness of lithosphere, amplitude of mantle-driven vertical surface motions, basin uplift and subsidence. Common assumptions about isostasy are not always justified by existing data. For example, refraction seismic data provide essential constraints to estimation of isostasy, but are rarely analysed in that respect. Average seismic velocity, which is an integral characteristic of the crust to any given depth, can be calculated from initial refraction velocity models of the crust. Geoscience Australia has 566 full crust models derived from the interpretation of such data in its database as of January 2012. Average velocity through velocity/density regression translates into average density of the crust, and then into crustal column weight to any given depth. If average velocity isolines become horizontal at some depth, this may be an indication of balanced mass distribution (i.e., isostasy) in the crust to that depth. For example, average velocity distribution calculated for a very deep Petrel sedimentary basin on the Australian NW Margin shows no sign of velocity isolines flattening with depth all the way down to at least 15 km below the deepest Moho. Similar estimates for the Mount Isa region lead to opposite conclusions with balancing of average seismic velocities achieved above the Moho. Here, we investigate average seismic velocity distribution for the whole Australian continent and its margins, uncertainties of its translation into estimates of isostasy, and the possible explanations for misbalances in isostatic equilibrium of the Australian crust.

The seismic survey was carried out at the request of the U.K. Ministry of Supply. The purpose of the survey was to disclose the geological structure and, if possible, the physical rock characteristics at the Maralinga testing ground. The 11,000 ft/sec layer at a depth of about 200 ft, probably a sandstone-shale formation, and the 19,000 ft/sec formation at a depth of about 1350 or 1800 ft (according to the method of computation used) were successfully mapped. The subsurface information to a depth of about 200 ft was derived mainly from shallow drill holes and up-hole shots. An experimental spread indicated a very low Poisson ratio for the sandstoneshale formation.

A seismic velocity survey was carried out in Associated Freney Oilfields Nerrima No. 1 Bore by the Bureau of Mineral Resources on the 10th August 1955. The well is situated on the Nerrima Dome in the Fitzroy Basin, W.A. Some trouble was experienced with cable breaks for the shallow part of the hole, but in general it was possible to recognise the true formation break. Average measured velocities ranged from 8000 ft/sec near the top to 12,200 ft/sec for the total depth of the bore.

This report contains the results of a seismic survey on the Nerrima Dome, a major structure within the Fitzroy Basin and near its south-western boundary. The dome is situated near the Fitzroy River about 100 miles south-east of Derby in the West Kimberley district of Western Australia. The Nerrima Dome has been mapped at the surface in Permian sediments and is a complex structure. It was desired to determine if the dome existed at depth and, if not, the structure at depth, with a view to locating a site for a deep drilling test. The target beds for such a test are Devonian and/or Ordovician sediments over which the Permian sediments are believed to lie unconformably. Reflection methods were tried and proved unsuccessful and the survey was carried out using refraction methods. Although the structure underlying the dome has not been clearly shown, the refraction method has indicated that it is complex and does not conform with the domal structure at the surface. There appears to be a major unconformity at comparatively shallow depth (2000 ft). The deep structure (7000 ft) although apparently less complex than that immediately below the unconformity, also bears no obvious relation to structure at surface. The results so far obtained are reasonably conclusive in showing that no simple dome-like structure of large magnitude exists under the Nerrima Dome.