AusMT / surveys / Southwest Australia Traverse 1966

Southwest Australia Traverse 1966 GDS

Geomagnetic depth sounding survey · Western Australia · Australian National University

Part of the Australia legacy GDS collection

Between June and September 1966 J.

About this survey

Between June and September 1966 J. E. Everett and R. D. Hyndman of the Australian National University carried three sets of portable three-component magnetometers across the Precambrian shield of south-western Australia, occupying ten stations in turn, from Rawlinna on the Nullarbor Plain west to the coastal plain near Perth and south to Esperance. It is the earliest survey in this collection and belongs to the first years of geomagnetic induction research in Australia. They set out to measure how far inland the coast effect persists over a shield, and what that implies about the conductivity beneath it.

The instruments, built in the ANU's Department of Geophysics and Geochemistry, measured each field component to one gamma once a minute and punched the values onto eight-hole paper tape. Each station recorded for a few weeks, and the records were Fourier analysed on the CDC 3600 at the CSIRO computing centre in Canberra to give single-station vertical-field transfer functions at periods of about 1,440 to 43,200 s, the paper's 2 to 60 cycles per day. Everett and Hyndman found the coast effect persisting about two and a half times further inland over the shield than on the eastern Australian and Californian coasts, falling to the same level at about 250 km rather than 100 km, and read the difference as a lower conductivity beneath the shield, in keeping with its low heat flow. On the west coast the effect grew inland before it faded, which they explained by a narrow strip of more conductive non-shield crust west of the Darling Fault. At four stations, Rawlinna, Kalgoorlie, Coolgardie and Tammin, horizontal electric fields were recorded as well, between copper and copper sulphate electrodes about half a kilometre apart. These gave the first magnetotelluric soundings reported in Australia and a two-layer model with a conductive layer below about 200 km, and they connect this early depth-sounding work directly to the magnetotellurics that followed.

The served values are ten single-period vertical-field transfer functions, one complex value per station at a period of 3,600 s. They come from Liejun Wang's Australian Electromagnetic Database, the register compiled at the Australian National University, whose rows for this survey are understood, though not documented, to be a digitisation of the 3,600 s induction arrows mapped in Figure 5, printed p. 30, of Everett and Hyndman, Physics of the Earth and Planetary Interiors 1, 24 to 34 (1967). The coordinates are the register's own, and they agree within a kilometre at every station with the positions printed in Table 1 of that paper, p. 26, and at nine of the ten with Table 9.1 of Hyndman (1967), whose Coolgardie longitude is a printing slip. The original recordings are not held.

Data and downloads

Stations (10)

Contributors and organisations

Organisation

Australian National University

Licence

CC BY 4.0

Identifiers and provenance

Machine-readable survey record · catalogue schema mtcat 2.0