These notes deal with a brief experimental seismic survey undertaken by the Bureau of Mineral Resources for the Victoria Railways. The object of the survey was to determine whether the seismic refraction method was suitable for subsurface exploration in the area between Dynon and Footscray Roads, West Melbourne. The information desired by the Railways was concerned with the existence or otherwise of a "foundation" rock capable of supporting constructions associated with railway sidings and marshalling yards. Records of seismic refractions were obtained along three traverses.

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.

At the request of the State Rivers and Water Supply Commission of Victoria, seismic tests using the refraction method were conducted over six well locations near Cobram in the Murray Valley Irrigation District of Central Northern Victoria. The purpose of the tests was to determine whether the depth of the water table in that area could be measured by seismic refraction methods. The problem of rising water tables is one which occurs commonly in irrigation districts. In some areas the problem is purely a local one in which only perched water tables, any within ten feet of the surface, are involved, but it is also possible that the level of the general water table over a large are may be raised by deep percolation. The State Rivers are Water Supply Commission have maintained a check on the water table depth in the Murray River Valley Irrigation District for some time by measurement in existing wells. These wells are not necessarily in the best positions, and some are falling in. The seismic method was considered as an alternative to expensive test boring for ground water measurement.

The Fenton Fault, one of the major tectonic lines in the Canning and Fitzroy Basins, has always presented a major problem to geologists seeking to determine its true nature and significance. The investigation described in this report was intended to contribute towards a solution of the problem. This investigation included a seismic reflection traverse across the Fault in the area of Barnes Flow, near where previous gravity and airborne magnetic traverses had crossed it, together with refraction traverses on each side of and across the fault. The results of previous surveys are discussed, and show that the gravity meter is a most useful tool for the further investigation of the Fenton Fault. However, unless new and effective treatment of results can be devised, it is of doubtful value in investigating folding within the Fitzroy Basin, though this does not necessarily detract from its value for regional surveys. The airborne magnetometer on the other hand, is not a reasonable tool for investigating the Fault. It is concluded that the Fenton Fault at Barnes Flow is a normal fault, downthrown to the north-east, with a throw probably exceeding 10,000 feet. The thickness of the sedimentary section on the north side of the Fault near Barnes Flow probably exceeds 16,000 feet. On the south side a velocity of over 20,000 ft/sec. was recorded from a depth of 5,500 feet. This probably indicates the depth to basement at this point. On the south side of the Fault at Jurgurra Creek the sedimentary section appears to be about 7,000 feet thick. The conclusion that baaement is relatively shallow to the south of the fault could be tested by drilling. The rig used should be capable of drilling to at least 6,000 feet to ensure that the 20,000 ft/sec. refractor may be penetrated and identified.

An experimental seismograph survey was carried out near Heywood in the Western District Basin, south-western Victoria, during November and December, 1956 by the Bureau of Mineral Resources, Geology and Geophysics. The work was requested by Frome-Broken Hill Pty. Ltd. and was intended primarily to ascertain if reflections from deoper sediments could be recorded through a surface layer of basalt which covers considerable areas in the Western District of Victoria. Several short traverses were shot during the survey at places where a variety of surface conditions for seismic exploration could be tested. Pattern and air-shooting techniques were tried as well as the conventional single shot-hole technique. Good reflections were recorded from depths down to eleven thousand feet in areas where there was no basalt. Some apparent reflections of poor quality were recorded at times as great as 5 seconds after the shot was fired. An attempt has been made to correlate the reflections with stratigraphic horizons. Reflections were obtained from strata beneath a basalt cover in some places when explosive charges were fired in single shot holes; reflection quality was improved when pattern and air-shooting techniques were used.It was not possible to record reflections through a cover of tuff containing basalt bands on the slopes of Mt. Clay. Pattern and air-shooting were tried unsuccessfully. Sub-surface information in the Heywood area is obtainable by seismic exploration and techniques for gaining the best information from the seismic method are discussed.

In July and August 1957 an experimental seismic survey was done in the Oodnadatta area of the Great Artesian Basin. The purposes of the survey were to find whether reflections could be recorded from beneath duricrust, a siliceous surface deposit, and whether structures mapped by surface geological methods persist with depth. Reflections were recorded from beneath the duricrust using shallow pattern holes and six geophones per trace; the sub-surface structure was mapped with reasonable accuracy. In areas where the duricrust is eroded, reflections of fair quality were obtained using a single shot-hole and six geophones per trace. A seismic reflection traverse across the Oodnadatta anticline indicated that the structure was present in a horizon which corresponds to the top of the artesian aquifer at a depth of about 1000 ft below datum (400 ft above MSL). The seismic results indicated that the anticline was of smaller relief than had been e stimated from surface mapping. There was a change from fair-quality persistent reflections at shallow depths to poor-quality less numerous reflections with sporadic dips at greater depths; this probably represents the base of the Cretaceous. The greatest depth from which Cretaceous sediments were recorded was about 2350 ft below datum. Reflection depths computed by seismic methods correspond closely with lithological boundaries, and in particular the base of the Cretaceous sediments, encountered in the Santos No. 1 bore. The results of a refraction traverse on the crest of the Oudnadatta anticline show the presence of a 'basement' refractor with a velocity of 13,900 ft/sec at a depth of about 1245 ft below datum. There is slight evidence of a refractor with a substantially higher velocity at about twice this depth. The 'basement' velocity of 13,900 ft/sec is consistent with the assumption that there is a pre-Cretaceous layer between the Cretaceous sediments and the Precambrian basement complex.

A reconnaissance seismic survey was made in the area of Quilpie and Et.omanga in south-western Queensland. Traverses crossed the Harkaway, Pinkilla, and Tallyabra Domes. Reflection horizons were correlated with horizons within the Mesozoic sediments, and one persistent reflection was correlated with a horizon near the top of the Palaeozoic sediments. A thickness of sediments of up to 15,000 ft, including up to 11,000 ft of Palaeozoic rocks, was indicated on the flanks of the Harkaway and Pinkilla Domes. Results were compared with existing gravity data. Suggestions of faulting are based on seismic and gravity evidence taken together and also on gravity evidence alone in locations not covered by the seismic work.

In October and November 1959 a seismic party from the Bureau of Mineral Resources carried out a seismic survey in the Surat Basin, Queensland at the request of Australian Oil and Gas Corporation Ltd. A traverse extending from Surat eastward to within 10 miles of Tara was shot in five-mile sections of continuous reflection profiling with approximately five-mile intervals between the sections.^In addition two refraction traverses were shot near Surat to record velocities and depths of as many horizons as possible. Reflections were of fair to good quality throughout the survey and it was possible to correlate bands of reflections from one five-mile section to the next with considerable certainty. Over most of the traverses four reflecting horizons were followed, and in a few places reflections were obtained from a still deeper fifth horizon. The reflection survey revealed a wide basin between Surat and Cabawin (about 70 miles east of Surat), with its maximum thickness of sediments under Meandarra. The sediments there appear to be at least 19,000 ft thick. A marked anticline was discovered near Cabawtin. The refraction survey, using the "Depth Probing" method, revealed a refractor with a calculated velocity of 20,180 ft/sec situated about 1000 ft below the fourth reflecting horizon.

During 1961 in the southern part of the Surat Basin a seismic party from the Bureau of Mineral Resources surveyed two main traverses by means of seismic reflection and refraction methods; the first was in an east-west direction between Yelarbon and St George and the second was in a north-south direction between Meandarra and Nome. The main purposes of the survey were to find whether the Bowen Basin Permian sediments extend as far south as the latitude of Goondiwindi and whether the Bowen Basin in Queensland and the Sydney Basin in New South Wales formed a continuous region of sedimentation during the Permian period. The east-west seismic traverse indicated a trough of sediments of greatest thickness,tabout 14,800 ft beneath Toobeah; the trough is bounded on the eastorn side at Goondiwindi by a fault down-thrown more than 7000 ft to the west and is bounded on the western side by a series of step.-faults beneath Bungunya and Talweod. The results along the north-south traverse indicated that the trough beneath Meandarra, which represents the southern extension of the Bowen Basin, continues south to Toobeah. The nature of the link, if any, between the Bowen Basin and the Sydney Basin was not established. On the eastern side of the Surat Basin, seismic results indicated that the rocks beneath the Mesozoic sediments are stratified and probably metamorphic. A shelf area between Talweod and St George has about 6000 ft of sediments above a Drobablo metamorphic 'basement'. An anticlinal structure with a dip-reversal of about 1000 ft throw was located between Goondiwindi and Toobeah.

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