The Carpentaria Conductivity Anomaly of western Queensland is a major element in the electrical conductivity structure of the Australian continent. Investigation of it is significant both for its own sake, and as a case history in the general understanding of continental conductivity structure. Following its earlier discovery by reconnaissance magnetometers arrays, detailed magnetotelluric observations were carried out in 1997 along a transect crossing the anomaly between Cloncurry and Julia Creek. The magnetotelluric results define a good conductor within the crust beneath the sediments of the Eromanga Basin. The conductor extends over a depth range of tens of kilometres. This structure, evidently shown also by aeromagnetic and gravity data, is interpreted as the eastern boundary of the Mt Isa Block at a plate suture, which was later covered by the sediments of the Eromanga Basin. Seismic tomographic results show a major gradient in seismic-wave speed in the region. It appears the potential-field, electromagnetic and seismic methods have detected different characteristics of the same geologic structure, with complementary results. The electromagnetic results, new to this paper, define horizontal position well, and give evidence of highly conducting material from the crust to a depth of tens of kilometres. The seismic results extend the depth of the boundary into the upper mantle. The case history supports the hypothesis that the major conductivity anomalies of the geomagnetic deep-sounding method mark continental sutures of fundamental significance in recording the creation of continents.

The spin self-sustaining atomic magnetometer has the advantage of 1/τ measurement and great development potential in many applications. In this paper, we investigated the main elements that affect the stability and accuracy of the self-sustaining magnetometer and proposed the methods to improve its performance based on the measurement results. The correlation coefficient between fluctuations of the magnetic field generated by coils and the spin Larmor precession frequency is 0.97, which mainly dominates the stability in a short term. The accuracy of the magnetometer is affected by the power and frequency of the pump light. The Larmor precession frequency coefficient related to the pump light power is 26 mHz/mW, and the effect on the Larmor precession frequency is minimized when the pump light frequency is red detuned by 200 MHz from the 85Rb transition D1 line F = 3 to F′ = 3. The 1/τ measurement time after these corrections can be extended to 10 s, and the sensitivity achieved is 149 fT/Hz, which is close to the quantum projection noise limit of the system.

The absolute measurement of magnetic fields can be realized by monitoring the Larmor precession of atomic spins. Yet, this spin-precession magnetometer can only be put into use in weak magnetic fields and the sensitivity is limited by the coherence time beyond which, the uncertainty decreases as τ−1/2 rate. Now we demonstrate that the dynamic range of an atomic spin magnetometer can be extended to geomagnetic field magnitude with τ−1 property maintained based on the the self-sustaining method. A mean sensitivity of 20 pT/Hz and a frequency response bandwidth of 5 kHz are realized in a magnetic field of 10000 nT. More important applications in large magnetic fields can be enabled in virtue of the superiority using this self-sustaining magnetometer.