AusMT / surveys / Broken Hill 2002

Broken Hill 2002 GDS

Geomagnetic depth sounding survey · New South Wales, South Australia · Adelaide University

Part of the Australia legacy GDS collection

A magnetotelluric and geomagnetic depth sounding survey across the Olary and Broken Hill domains of the Curnamona Province, eastern South Australia and western New South Wales, acquired in winter 2002 by Rob Gill for an University of Adelaide honours project under Graham Heinson.

About this survey

A magnetotelluric and geomagnetic depth sounding survey across the Olary and Broken Hill domains of the Curnamona Province, eastern South Australia and western New South Wales, acquired in winter 2002 by Rob Gill for an University of Adelaide honours project under Graham Heinson. The traverse extended from the Kalkaroo area northwest of Broken Hill to approximately 40 km southeast of Broken Hill along the Menindee road and was oriented approximately perpendicular to the Mundi Mundi Fault. It followed a similar corridor to an earlier seismic reflection profile and was designed primarily to investigate the crustal boundary between the Olary and Broken Hill domains and assess whether the Mundi Mundi Fault represents that boundary.

Seventeen sites were deployed at approximately 10 km spacing using four Flinders University high-frequency MT instruments originally developed for marine acquisition and modified for land use. Each instrument used a fluxgate magnetometer and two orthogonal electric-field dipoles formed from CuSO4 ceramic-pot electrodes. The north and east electrode leads were 100 m and the south and west leads 20 m, giving 120 m dipole lengths. Instruments were buried approximately 10 cm below the surface and recorded at 20 Hz, initially for about two days and subsequently for approximately one day per deployment. Multiple instruments were synchronised so that simultaneously operating stations could be used as remote references.

The field experiment identified significant problems with the electric-field measurements. Electrode performance was affected by the very dry soil, loss of CuSO4 electrolyte through seepage or evaporation, disturbance of electrodes and cabling by animals, and probable leakage within the amplifier electronics under high contact impedance. At some sites the two electric channels consequently became anomalously similar. The magnetic measurements were considered reliable, whereas the impedance-derived apparent resistivity and phase responses were not used for the subsequent two-dimensional interpretation.

The original binary recordings were converted to one-second averaged ASCII data and processed using Alan Chave's robust remote-reference MT program RRRMT. Both MT and geomagnetic depth sounding transfer functions were calculated, with the magnetic data providing vertical magnetic-field transfer functions and Parkinson induction arrows. These responses were subsequently imported into WinGLink and the vertical-field transfer functions were used for two-dimensional inversion. The resulting model identified a major resistivity transition near the Mundi Mundi Fault, separating the highly resistive Broken Hill Domain to the east from more conductive crust to the west, and detected the eastern margin of the Flinders Conductivity Anomaly near the western end of the traverse.

Seventeen sites were deployed during the field survey, of which AusMT serves vertical magnetic-field transfer functions for 15 sites. The served responses contain 18 to 24 periods spanning approximately 11 to 2048 s and were reconstructed from induction-arrow tables produced during a 2007 reprocessing of the 2002 recordings held in the University of Adelaide geophysics collection. The surviving tables contain no uncertainty values. Two Kalkaroo sites have no surviving induction-arrow data in the holding, and no response is available for site B-12. Site coordinates and elevations are taken from the associated station records; the B-06 longitude printed in the original thesis is inconsistent with the archived station position. The original time-series recordings are not held in the collection.

Data and downloads

Stations (15)

Contributors and organisations

Organisation

Adelaide University

Licence

CC BY 4.0

Funding

Adelaide University
Geological Survey of South Australia
Australian Society of Exploration Geophysicists

Publications

Gill RM (2002). A magnetotelluric profile across the Broken Hill and Olary Domains. B.Sc Hons Thesis, University of Adelaide. http://hdl.handle.net/2440/113040

Identifiers and provenance

Machine-readable survey record · catalogue schema mtcat 2.0