Research Activities

Introduction

Research into the structure and dynamics of the Earth uses a range of modern physical and mathematical techniques grouped into four themes of Geodynamics, Geophysical Fluid Dynamics and the Centre for Advanced Data Inference (CADI). Work in the Earth Physics area spans observational, theoretical, computational, and data oriented studies that are all directed towards understanding the structure and processes in the solid and fluid Earth, and their environmental consequences. The four themes in Earth Physics have considerable cross-interaction, particularly through a common use of computational methods.

Prof. B.L.N. Kennett, the Area Coordinator, was awarded the Jaeger Medal for Australian Earth Science from the Australian Academy of Sciences in May 2005 and at the end of the same month was elected as a Fellow of the Royal Society of London.

Work in geophysical fluid dynamics this year includes a new theoretical model for the thermohaline overturning circulation of the oceans, based on insight from laboratory experiments on turbulent entrainment. Experimental runs in the GFD laboratory have been linked to major computational simulations, e.g. in understanding the amount of mixing that takes place in density-driven exchange flow through constrictions, such as ocean straits. Other classes of laboratory investigations include studies of lava flow dynamics, particularly in pre-existing channels and three-dimensional simulations of subduction to understand the flow around subducting plates.

Studies of the interaction of mantle dynamics with mantle chemistry, with the aid of numerical models, suggest that early plate tectonics is a more viable concept than previously thought, which would change the expected cooling history of the mantle. Further the age of mantle trace components depends little on the viscosity structure but mainly on the rate of processing through zones of melting.

In seismology, the long running Tasman Line experiment was completed this year and all 20 stations have been recovered. This data has made significant contributions to the resolution of structure in the neighbourhood of the transition from Precambrian to Phanerozoic Australia, both from surface wave tomography and in the mapping of crustal structure using receiver functions. The improved resolution of lithospheric structure suggest the presence of three steps in lithosphere thickness in the transition from the cratonic core in the west to the eastern seaboard of the continent.

A deployment of short-period instruments in the Murray Basin has provided important tomographic constraints on structures beneath the basin. A further major deployment has been made in Eastern Victoria that will run to mid 2006, and when linked with previous data should provide high density of station coverage across the whole of Victoria.
Waveform correlations methods have been successfully employed on data from the Tasman Line experiment to provide new constraints on crustal and upper mantle structure from surface wave analysis.

In the Centre for Advanced Data Inference projects have been conducted in geomorphology, probability theory, statistical inference techniques, structural seismology, airborne geophysics, earthquake seismology, computational mineral physics and geodesy. This year saw continued development of the CADI inversion toolkit whereby CADI visitors and project participants have a simple interface to both software and hardware facilities including the Terrawulf parallel cluster.

The focus of the glacial rebound work in 2005 has focussed on Arctic Eurasia from the time of the penultimate glacial maximum (MIS 6 or the Late Saalian at ~145,000 years ago) up to the present with the goal of establishing constraints on the ice thickness and ice margins for some of the major phases of the last glacial cycle. A major compilations of field evidence for the ice margin locations and shoreline elevations and sea levels across the region has been completed and the inversion of which has led to new ice models from 140,000 years to 60,000 years ago, including the time of the renewed initiation of the ice sheets after the last interglacial.

Geodetic research during 2005 produced significant improvements in the accuracy of the analysis of GPS, primarily through software developments made at RSES in modelling geophysical phenomena such as atmospheric pressure loading, ocean tide loading and atmospheric propagation effects. A successful GPS field observation program was carried out in Papua New Guinea on a transect of sites along the western border, in the Schouten Islands, central Highlands and the Papuan Peninsula region.

Geophysical Fluid dynamics
Geodynamics
Seismology and Geomagnetism
CADI