Despite long history of studies the Wallaby Plateau offshore Western Australia remains a controversial feature. Analysis of interval seismic velocities from Geoscience Australia's 2008/09 seismic survey 310 in conjunction with seismic reflection interpretation provides new insights into the geology of the Plateau. Seismically distinctive divergent dipping reflector (DDR) packages have been identified. The seismic character of the DDR packages is similar to seaward dipping reflector (SDR) packages of inferred volcanic composition. Initial analysis of seismic velocity profiles indicated affinities between the DDR packages and known sedimentary strata in the Houtman Sub-basin. Effect of water loading on seismic velocities is commonly ignored in offshore studies. However, direct comparative analysis of interval velocity patterns between areas of significantly different water depth requires various water pressure related changes in velocity to be accounted for. There are controversies in methodology and application of water depth adjustment to seismic velocities, and presentation of velocity models as function of pressure rather than two-way time, or depth emerges as a possible solution. Water depth adjustment of seismic velocities analysed in our study reduces distinction between SDRs, DDRs and sedimentary strata such that discrimination between volcanic and sedimentary strata in DDR or SDR packages is equivocal. A major uncertainty of this interpretation is due to a lack of the reference velocity model of SDRs and DDRs investigated globally.

Stacking velocities for surveys 1001 (Shell Petrel) and 1053 (Esso R74A) over the Bremer and Denmark Sub-basins were analysed for depth and time.

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.

The Undilla Basin, in north-western Queensland, is a small sedimentary basin containing Cambrian limestones which adjoin the widespread but undated CamoowJal Dolomite to the West. In the latter part of 1961 the Bureau of Mineral Resources, Geology and Geophysics did a brief reconnaissance seismic survey lasting about seven weeks in the Undilla Basin. This Record describes briefly the work done and results obtained. The occurrence of limestone near the surface throughout the basin presented difficult problems in the application of the reflection and refraction seismic methods but some progress was made towards the solution of these problems.

Aeromagnetic and gravity surveys were made in the Tambo-Augathella area by Magellan Petroleum Corporation in 1959 and 1960 respectively. A probable fault shown in the magnetic interpretation is almost coincident with a zone of steep gravity gradients which was interpreted as indicative of a fault or of steeply dipping strata. However, the normal gravity interpretation would indicate a deeper cross-section to the south-east of this zone, whereas the magnetic interpretation suggests that the fault is downthrown to the northwest. The present survey was undertaken by the Bureau of Mineral Resources to find out which interpretation was the more probable. A reflection seismic traverse was shot at right angles to the closed gravity 'high' and across the zone of steep gravity gradients. Results show that the closed gravity 'high' is the expression of an anticline and that the zone of stoep gravity gradients is caused by steep dip to the south-east on the flank of the anticline. The gravity interpretation is therefore found to be more representative of actual conditions.

A seismic survey, consisting of a main north-south reflection traverse and several short supplementary reflection and refraction traverses, was made in the Gosses Bluff area, of the Amadeus Basin,Northern Territory by a seismic party of the Bureau of Mineral Resources, Geology and Geophysics between March and July 1962. The purpose of the survey was to obtain information on the lli.ssionary Plain Syncline, the Gosses Bluff uplift; the fault at the northenl flank of the Gardiner Range, and the tectonic features relative to the Archaean/sedimentary contact at the northern edge of the Missionary Plain. The seismic reflection method proved to be an excellent exploratory tool in the undisturbed parts of the sedimentary basin. The Missionary Plain Syncline was shovm. to have a maximum thickness of sediments of 33,000 ft, nine miles north of Gosses Bluff. The results indicate that Gosses Bluff is a diapiric structure of the salt dome type, where the Proterozoic Bitter Springs Limestone has provided the necessary mobile material. The Gardiner Range Fault was shown to be overthrust from the south vdth a hade of 15 to 20 degrees. The problem regarding the Archaean/sedimentary contact was not solved.

Between April and July 1962, a seismic party from the Bureau of Mineral Resources, Geology and Geophysics made a seismic reflection and refraction survey in the Moree area of New South Wales. The main purpose of the survey was to investigate whether the southern extension of the Bowen Basin beneath the Great Artesian Basin from Meandarra to Toobeah continued as far south as Moree and joined the Sydney Basin. Three east-west traverses were shot using a method of reconnaissance reflection shooting, the first near Dolgelly Bore, the second through Moree, and the third through Bellata. The third traverse was extended eastward as far as the Horton River to investigate the Hunter-Bowen Thrust zone. In addition, three north-south refraction traverses were shot in the middle, and on both ends, of the east-west traverse through Moree. A north-south reflection traverse was shot north of Dolgelly Bore.Results in the Moree and Bellata areas were of poor quality and in the Bellata area in particular, owing to surface basalt flows, little information was obtained. The Hunter-Bowen Thrust area was not distinguished by the seismic work. The seismic results indicated that the trough of sediments extending southwards through Dolgelly Bore was at least 7500 ft deep south of Dolgelly Bore. The eastern margin of the trough is probably an overthrust fault. In the Moree area, two troughs were indicated, viz. the Biniguy Trough in the east where about 7000 ft of sediments was estimated separated by the Pallamallawa Ridge from the Moree Trough in the west where about 11,000 ft of sediments was estimated. Poor results in the Bellata area failed to indicate whether the Moree Trough joined the Sydney Basin.

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.

This Record describes a seismic refraction survey made during 1961 in the Farm Area, Alice Springs, NT. Good refraction breaks were obtained only along the east-west Traverse K; the refraction breaks along the north-south traverses were very poor. Velocities indicated in the overburden are interpreted in terms of particular geological formations within the Mesozoic and Recent sediments. Results along additional east-west traverses would be needed before a similar interpretation could be applied to the bedrock velocities.

A four and a half month seismic survey has been carried out in the Poole Range area of the Fitzroy Basin by C. G. G. where both the reflection and refraction methods have been tested. Reflection experiments lead to a high multiplication of geophones and shot-holes patterns. However, tests were too limited and too scattered to allow for definite conclusions regarding the best recording procedure. The refraction method has been used to provide information regarding the extension at depth of Poole Range surface anticline. The same method was used for a reconnaissance survey on the regional gravity anomaly 16 A. Besides shallow markers, two and sometimes three deep markers were followed simultaneously. The results obtained during the survey indicate that: Poole Range surface structure has no extension at depth; - Two high zones, separated by a narrow trough appear to correspond to the gravity anomaly 16 A. The eastern high zone is a wide dome with a closure of about 4,000 ft at the level of the deeper marker. The western high zone corresponds to a shelf-like area of the deeper marker. It is overlain by sedimentary formations where facies changes are suggested by rapid variations of the marker's velocities. This is the shallowest area of the survey with a 15,000 ft/ sec marker at a depth of less than 10,000 ft. Delimination of the most interesting structural locations would require the carrying out of supplementary traverses. A tentative interpretation makes the deeper marker a probable Proterozoic level with depths ranging from 15,000 feet to 30,000 feet. The two others might represent Devonian and Ordovician formations.