Seismic Imaging Results From a Decade of Rolling Array Deployments in Southeast Australia
Abstract
Over the last decade, twelve seismic arrays have been sequentially deployed as part of the WOMBAT experiment to cover a large area of southeast Australia at station spacings varying between 15 and 50 km. Each array typically consists of between 30 to 60 short period instruments that continuously record for between five to ten months. Early deployments used vertical component seismometers, but these were upgraded to three component in 2006. To date, a total of over 500 sites have now been occupied, resulting in a very large passive seismic dataset. A vast majority of earthquake sources detected by the arrays are teleseismic, originating from the margin of the Australian plate and beyond. Other useful sources of seismicity include local earthquakes (although not very numerous) and ambient noise generated from oceanic and atmospheric disturbances. A variety of research has been carried out with the recorded data, but the bulk of effort has been directed towards lithospheric imaging using seismic tomography. Separate teleseismic tomography studies have been published for six of the arrays, but the focus is now on joint inversion using all available datasets. A long term goal of WOMBAT is to try and constrain a detailed 3-D lithospheric model of the region by utilizing all available data, including teleseismic, local earthquake, active source (available in a few places) and ambient noise. In addition to teleseismic traveltime tomography, we have recently extended our investigations to include teleseismic receiver functions and ambient noise tomography. In the latter case, traveltime information extracted from long term cross-correlations of waveforms recorded by pairs of simultaneously recording stations has allowed detailed maps of Rayleigh wave group velocity to be constructed. These maps resolve shallow, mid and deep crustal structure, and clearly discriminate between sedimentary and hard rock regions. For example, the Sydney Basin, Gippsland Basin and Renmark Trough are all clearly revealed by low velocity anomalies. Recently, teleseismic traveltime residuals from two separate arrays (TIGGER and SETA) were combined with wide-angle data from an active source experiment to produce a 3-D P-wave model of the Tasmanian lithosphere. Synthetic reconstruction tests show that crustal velocity, Moho geometry and mantle velocity are well resolved by the overlapping datasets. One of the main results from this study is that the transition from the Precambrian West Tasmania terrane to the Phanerozoic East Tasmania terrane is clearly marked by a distinct shallowing of the Moho and increase in crustal velocity. Combined with evidence from geological mapping and rock dating, these results support the idea that the two crustal elements once formed a passive margin in the Cambrian.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.S43D..01R
- Keywords:
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- 7205 SEISMOLOGY / Continental crust;
- 7218 SEISMOLOGY / Lithosphere;
- 7270 SEISMOLOGY / Tomography