HR: 09:30h
AN: S11E-07    [Abstracts]
TI: 3-D Teleseismic Tomography of the Crust and Upper Mantle Beneath Northern Tasmania, Australia
AU: * Rawlinson, N
EM: nick@rses.anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia
AU: Kennett, B L
EM: brian@rses.anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia
AU: Reading, A M
EM: anya@rses.anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia
AB: The TIGGER project is a multi-faceted seismic study of Tasmania and southern Victoria (SE Australia) undertaken by the Australian National University in 2001/2002. As part of this project, an array of 72 short period and broadband seismic recorders with a nominal spacing of 15 km was deployed across northern Tasmania for a period of five months. To date, nearly 6,000 relative arrival times from 100 earthquakes have been picked using a newly developed and robust adaptive stacking technique. The azimuthal coverage of teleseisms is generally good, with many events to the north and east (e.g.~Indonesia, Papua New Guinea, New Zealand, Fiji), although fewer from the south and west(e.g.~South Sandwich Islands, mid- Indian ridge). A new iterative non-linear tomographic inversion procedure based on the fast marching method (FMM), a grid based eikonal solver, and a subspace inversion scheme, is used to map traveltime residual patterns as P-wave velocity anomalies from an {\em ak}135 reference model. The 3-D model volume beneath the array is parameterized using cubic B-spline functions in spherical coordinates; a total of nearly 10,000 vertices at approximately 15 km grid spacing is used to describe the TIGGER model. Preliminary tomographic results from the TIGGER experiment show significant lateral variations in P-wave velocity structure within the Tasmanian lithosphere. Geological inferences made from these early results include: (1) Within the crust, the first-order E-W velocity variations strongly support the idea that eastern Tasmania is underlain by dense rocks with an oceanic crustal affinity, contrasting with the continentally derived lower crustal rocks of western Tasmania; (2) the Tamar Fracture System, often defined as a lithospheric scale discontinuity, probably does not exist; (3) the elevated crustal velocities beneath the Rocky Cape Group and Arthur Lineament, compared to the Tyennan Element and Mt. Read Volcanics to the east, also support a mafic-felsic compositional variation in the deep crust, possibly caused by a collision-obduction event in the Cambrian; and (4) the pattern of velocity variations within the crust does not have a simple relationship to that in the mantle lithosphere beneath.
DE: 8180 Tomography
DE: 9330 Australia
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting