Is the Australian Plate deforming? A space geodetic perspective

Measurements at discrete points spanning the Australian Plate have been made for over a decade using the Global Positioning System (GPS) space geodetic technique. These measurements show that, to within the resolution of the technique (∼2 mm/y at 95% confidence level), there are no significant changes in the dimensions of the Australian Plate across the Australian continent. That is, no changes in baseline lengths are evident between any sites located in Australia when taking into account the measurement and modelling errors. However, during the past two decades, several significant earthquakes have occurred within the Australian Plate indicating that at times stress failure levels are reached, resulting in failure within the crust. Therefore, the rate at which stress accumulates must be slower than is visible in the geodetic measurements. With the exception of two sites affected by earthquake co-seismic displacement and equipment failure, all time series of sites in the interior of the Australian Plate are linear and site velocities are not significantly different from the predicted motion of the 'rigid' Australian Plate. However, the northern margin of the plate in Papua New Guinea is undergoing regional deformation. This Is probably a result of the Interaction with neighbouring plates and the proximity of the GPS site to nearby plate-boundary zones.