Geoinformatika 2017; 2(62) : 24-31 (in Russian) 

FEATURES OF THE VELOCITY STRUCTURE OF THE MANTLE OF AUSTRALIA ACCORDING TO SEISMIC TOMOGRAPHY

L.N. Zaets

Institute of Geophysics, NAS of Ukraine, 32, Palladin Ave., Kiev, 03680, Ukraine, e-mail: larysa_zaiets@ukr.net

Purpose. The aim of the paper is to analyze a three-dimensional P-velocity model of the mantle of Australia; to identify the features of the velocity distribution, their correlation with certain aspects of geotectonic as well as mani­festations of seismicity.

Design/methodology/approach. The 3-D P-velocity model of the mantle of Australia has been obtained applying the method of Taylor.s approximation to solve problems of P-waves arrival time seismic tomography introduced by V.S. Geyko.

Findings. The analysis of the three-dimensional P-velocity model of the mantle shows that the tectonic division of the Australian continent into three parts – the western, central (Australian plate) and the eastern (Paleozoic Tasmanian fold-thrust belt) – is seen in the velocity structure of the mantle over the entire depth (up to 2600 km). The divi­sion of the ancient part of the platform into the western (West Australian shield) and the central one is traced along the sole of the high-velocity layer of the upper mantle, the transition zone of the upper mantle. The western part of the platform has a more powerful high-velocity layer of the upper mantle in comparison with the central part of the ancient platform (on the surface it is lowered and covered by younger deposits The velocity structure of the mantle show them as stable, ancient structures. The eastern part – the Paleozoic Tasmanian fold-thrust belt – refers to the activated structures (low velocity to a depth of 575 km). The most intense high-velocity anomalies are characteristic of the transition zone of the upper mantle. At the bottom of the mantle beneath the basin Canning Ofiser, Eucla, there is a vertical area of low velocity reaching the upper mantle transition zone and then spreading to the east and west along the transition zone. We have detected placing of mineral deposits in the areas of low velocity spreading and their absence over-the-domain of vertical spread with low velocity anomaly of the lower mantle. The same applies to the locations of earthquake epicenters. In particular, one of the recent earthquakes in northern Australia (in May 2016 with a magnitude of 6) is situated over the area of low velocities spreading. Here, in the upper mantle transition zone, a maximum low-velocity anomaly is characteristic of the transition zone of the upper mantle.

Practical value/implications. The analysis of the model gives new material for studying the geodynamic regime of Australia. We have shown the behavior of the velocity layers of the mantle under different tectonic structures. We have also revealed the manifestations of ultra-deep fluid processes in the mantle and their correlation with the location of earthquakes and deposits on the surface.

Keywords: mantle velocity structure, Australia, seismic tomography.

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