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Geodynamics and geodesy Introduction

FTLRS in night operation

The geodynamics group within Earth Physics is involved in the Geospatial component of AuScope. NCRIS funding in this strand has enabled investment in geodetic infrastructure throughout Australia, including three new Very Long Baseline Interferometry (VLBI) sites, a national Global Navigation Satellite System (GNSS), terrestrial gravimeters, a test of a mobile Satellite Laser Ranging (SLR) system and a contribution towards the new Terrawulf II compute cluster. Members of the geodynamics group are involved in the AuScope Executive Committee, the Geospatial Steering Committee as well as the gravity, VLBI and Grid Computing subcommittees charged directly with the acquisition and deployment of the infrastructure. The ANU component of the above equipment includes an FG5 absolute gravimeter (acquired in April 2008), a relative gravimeter (acquired in July 2008), a gravity technician and a SLR technician. Dr Jason Zhang, the SLR technician, was involved in instrument testing at Burnie, Tasmania early in 2008 while Mr Geoff Luton has been involved in FG5 observations in Melbourne, Hobart and Western Australia.

The InSAR analysis of small, shallow earthquakes in Western Australia demonstrated the capability of the technique to not only estimate fault plane location, orientation and depth but also to estimate the distribution of slip on the fault plane (Dawson et al., 2008). The stress drop for the Mw=4.7 Katanning earthquake was found to be 14-27 MPa, significantly smaller than expected for such as small event. This suggests that the seismic hazard of small earthquakes might be higher than previously thought.

A combination of surface deformation from GPS and inferred deformation from changes in the Earth's gravity field from the Gravity Recovery and Climate Experiment (GRACE) have been undertaken to separate short-term hydrological variations from longer-term glacial isostatic adjustment as a result of melting of polar ice sheets since the Last Glacial Maximum. Coupled with continued advances in the analysis strategies of the raw GPS observations, these studies have revealed that both the GPS and GRACE estimates of surface deformation agree at the 1-2 mm level and mm/yr level, enabling highly accurate estimates of crustal deformation to be made.

Successful field experiments have been undertaken using the new gravimeters in Melbourne, Hobart and several sites in Western Australia. The GPS field programme in Papua New Guinea concluded this year while coral sampling in the Ningaloo Reef region continued in order to understand past levels of relative sea level.