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55% coverage west D53/B1-236 Vertical scale: 10

D53/B1-201 Vertical scale: 50

D53/B1-180 Vertical scale: 100

Gravity meters with a quartz mechanism can be calibrated on tilt tables, on hillside calibration ranges with stations at different altitude, or on level calibration ranges with stations at the same altitude. Twenty Worden, Sharpe, and Scintrex gravity meters have been calibrated in Canberra on a PEG-1 tilt table borrowed from the Soviet Academy of Sciences. These calibrations agree, to within experimental error, with tilt calibrations by the manufacturers in North America, and calibrations based on sea-level stations along the Australian Calibration Line. Calibrations on hillside calibration ranges differ systematically from other calibrations, and indicate a mean altitude effect of (2.5 ± 0.5) X 10^-3 um s^-2 m^-1. This altitude effect is higher than the mean of (1.5 ± 0.3) X 10^-3 micro m s^-2 m^-1 found by pressure-chamber studies in North America and Europe. If quartz-mechanism gravity meters are used either in base station gravity networks, or for field stations in areas with over 500 m of relief, then a correction should be made for this altitude effect, particularly if the anomalies are to be used for geodetic purposes.

The Great Artesian Basin occupies 1.7 X 10^6 km^2, or about one-fifth of Australia, extending across parts of Queensland, New South Wales, South Australia, and the Northern Territory. It underlies arid and semi-arid regions where surface water is sparse and unreliable. The discovery of the basins groundwater resources around 1880, and their subsequent development, have allowed an important pastoral industry to be established. Pastoral activity and town water supplies are to a very large extent dependent on artesian groundwater. The groundwater basin consist of a multi-layered confined aquifer system, with aquifers occurring in continental quartzose sandstones of Triassic, Jurassic and Cretaceous age. The intervening confining beds consist of siltstone and mudstone; a thick argillaceous sequence of sediments of marine origin and Cretaceous age forms the main confining unit. The basin is, in places, 3000 m thick, and forms a large synclinal structure, uplifted and exposed along its eastern margin and tilted southwest. Recharge occurs mainly in the eastern marginal zone, and large-scale groundwater movement is generally towards the southwestern, western and southern margins. Natural discharge occurs from spring in these areas; most springs are connected with structural features. Minor recharge occurs in the western margin. The potentiometric surfaces of the Triassic, Jurassic and Early Cretaceous aquifers are still above groundlevel in most areas of the basin. Considerable lowering occurred in heavily developed areas; from about 1880 to 1970, regional differences of up to 80 m were recorded, and in some areas waterwells ceased to flow. Water levels of some Cretaceous aquifers are below the groundsurface throughout most of the basin area. Hydraulic gradients of the main aquifers in the Lower Cretaceous-Jurassic sequence are about 1:2000, and of aquifers in the Cretaceous sequence 1:1800. Transmissivity values of the main aquifers in the Lower Cretaceous-Jurassic sequence, from which most flowing artesian wells obtain their water, usually are several tens to several hundreds m^2/day. Hydraulic conductivities range from 0.1 to 10 m/day, with a predominance in the lower part of the range. Storage coefficients, as interpreted from wire-line logs, average about 10^-5. Aquifer thicknesses range from several metres to several hundred metres. Average groundwater velocity in the eastern marginal parts is from 1 to 5 m/year. Environmental isotope analysis shows that the artesian water is of meteoric origin. About 4700 flowing artesian wells have been drilled to depths of up to 2000 m, but average 500 m. Individual flows exceeding 10 000 m^3/day have been recorded. About 3100 wells remained flowing during the early 1970s, when the accumulated artificial discharge was about 1.5 X 10^6 m^3/day, as compared to the maximum flow from the basin of about 2 X 10^6 m^3/day from about 1500 artesian wells around 1918. The high initial discharge in the early years of exploitation, which was caused by the release of pressure in the aquifers, gradually levelled off, and has now approached a steady-state condition, in which total basin discharge is roughly balanced by recharge. Non-flowing artesian water-wells mainly in the higher Cretaceous aquifers number about 20 000, and are generally shallow, up to several hundred metres deep, and are usually equipped with windmill-operated pumps, supplying on average about 10 m^3/day each. Most flowing wells occur in the marginal areas of the basin, as the main aquifers in the Lower Cretaceous-Jurassic sequence which they tap are too deep for economical abstraction in the central part of the basin. In the central part mainly non-flowing shallow wells are found.

The first Australian earthquake accelerograms were obtained from an accelerograph situated in the Dalton-Gunning region of New South Wales. Preliminary results were obtained for earthquakes on 23 November 1976 (maximum resultant acceleration 0.66 m/s^2), 30 June 1977 (0.21 m/s^2), 4 July 1977 (0.95 m/s^2) and 3 February 1979 (1.3 m/s^2). Maximum ground velocities were calculated for these earthquakes, and isoseismal maps drawn for the earthquakes at Bowning on 30 June 1977 and 4 July 1977. These data were used to test the validity of the relation Y = ae^bM R^-C for assessing ground motion, and hence determining seismic risk. Because of the uncertainties in the derivation of analytical expressions for ground motions, the fit to observed values of acceleration, velocity and intensity is considered to be good. The relation recommended for use by the Seismic Sub-Committee of the Australian National Committee on Earthquake Engineering included a depth-adjusting factor Co, where (R^2 = D^2 + h^2 + Co^2). When Co was omitted a better fit to the observed accelerations was obtained, but a poorer fit to observed velocities. The isoseismal pattern for the 4 July 1977 earthquake supports the radiation pattern expected from the faulting suggested by the focal mechanism and distribution of aftershocks. The isoseismals for the 30 June 1977 earthquake show a different radiation pattern; this suggests a different focal mechanism.

Possible economic hydrocarbon accumulations could exist in the Eromanga Basin sequence in southwest Queensland, particularly adjacent to faults transverse to groundwater flow. Interpretation of LANDSAT imagery and air-photographs indicates the probable presence of many faults hitherto unsuspected from field observations and seismic surveys. Most Jurassic and probably some of the more deeply buried Cretaceous rocks have generated hydrocarbons from relatively abundant source rocks, and under a variety of geothermal gradients. Hydrocarbons could also have migrated into the Eromanga Basin sequence from underlying basins whose equivalents elsewhere contain commercial accumulations.

Large trilobite resting traces (Rusophycus) from the Mithaka Formation are up to 30 cm or more in length, and are found in association with asaphid trilobites of similar length. The portion of the Mithaka Formation in which the Rusophycus occur contains a rich fauna and ichnofauna, and is considered to have been deposited in very shallow-water marginal to wide intertidal barrier flats behind a sand barrier.