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Seismology Introduction

2008 was an eventful year for seismic experiments, with the deployment of two new arrays, and the continued maintenance of the SEAL3 array which was deployed in late 2007. SEAL3 comprises 57 3-component short period stations distributed throughout southeast New South Wales at a spacing of approximately 50 km. With a recording period in excess of 1 year, this study has substantially contributed to the cumulative coverage of passive seismic data in southeast Australia. To date, nearly 400 sites have been occupied in Tasmania, Victoria, South Australia and New South Wales. Teleseismic tomography, ambient noise tomography, receiver functions and core phase studies are currently in progress using SEAL3 and pre-existing data.

In order to determine the nature of the transition at lithospheric depths between the northern and southern Australian cratons, a transect of 25 broadband seismic stations was deployed between the Eyre Peninsula in South Australia and Tennant Creek in the Northern Territory.  The installation took place in August-September 2008, with all stations expected to remain in operation for at least one year. With a site spacing of between 60-90 km, receiver functions, shear wave splitting and traveltime inversion can be utilized to help address fundamental questions relating to the anomalously slow velocities beneath the central Australian intercratonic structures, and how they propagate with depth.

Location of all short period seismic arrays deployed in southeast Australia over the last 10 years.

In June-July 2008, an array of 35 short period seismometers was installed across the Gawlor Craton in South Australia for an eight month period. Station spacing is approximately 50 km and the area covered runs from Port Lincoln in the Eyre Peninsular to Leigh Creek just west of the Flinders Ranges. The primary aim of this array is to increase passive data coverage in this part of Australia for seismic imaging, which includes teleseismic tomography and receiver function analysis. Local earthquakes, which are relatively plentiful in this part of Australia, will also be exploited to improve structural constraints. The eastern edge of the Gawler craton is currently of particular interest for the supply of geothermal energy and there are many ongoing industry projects in the area. Geoscience Australia completed a deep seismic reflection transect across the top of the Eyre Peninsular just prior to the deployment of the Gawler array. This array will provide broad scale earth imaging required for more detailed studies.

In 2008 the conversion of a large portion of our seismic data from past experiments to an international standard format called "miniseed" was accomplished. This is the first step in building a continuous archive of data, which is now easily accessible by local researchers through a java acquisition tool called Seismic Data Centre (SDC). About one half of our data has been converted and it is a work in progress. In other projects it was shown that it is not feasible to use 1D structural model for Australia when inverting for source parameters of large earthquakes surrounding Australia, and that a 3D model will be needed for the computation of Green's functions. This work is important in the context of the Tsunami warming for Australia. Work also commenced on the lithospheric structure of the Balkans peninsula using receiver functions, and an interactive tool (java) for forward modelling of receiver functions was completed. A large dataset from Antarctica was used to examine current hypotheses about the core anisotropy and structure showing in particular that the Antarctic data do not support the existence of significant heterogeneity in the outer core Taylor cylinder.