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Non-Linear tomographic inversion of active source seismic data: An investigation of the basement structure of Eastern Tasmania


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Lorimer, T 2007 , 'Non-Linear tomographic inversion of active source seismic data: An investigation of the basement structure of Eastern Tasmania', Honours thesis, University of Tasmania.

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A genetic algorithm has been developed for the inversion of seismic traveltime data and
applied to a tomographic investigation of central-eastern Tasmania. The investigation
used four shots and twelve stations across a 100 km east-west section of the post
Devonian cover of the Tasmania Basin. This area lies across the inferred but poorly
understood contact between the Eastern and Western Tasmanian Terranes, which has
proven difficult to image in previous geophysical studies.
The genetic algorithm developed in this project is portable across all parallel and
non-parallel Unix-based computing platforms, and interfaces with an existing, ad-
vanced, fast marching forward model code. The algorithm was applied both at low
resolution with subsequent model refinement by a subspace inversion method in a two-
step approach, and at higher resolution to directly invert the data using a one-step
approach. The one-step implementation yielded superior exploration of the model
space, and sufficient exploitation of the possible solutions when applied to the sparse
noisy data acquired during the controlled source investigation. This demonstrates the
viability of a one-step Monte-Carlo approach to seismic traveltime tomography in cases
of sparse data coverage.
The results of the inversions show a high velocity anomaly at 6 km depth and
147.4 degrees longitude, coincident with a long-wavelength magnetic anomaly, and is
interpereted as an ultramafic unit of possible oceanic crustal affinity. This supports
both thick and thin-skinned tectonic models with oceanic crust beneath the Eastern
Tasmanian Terrane, though the thin-skinned scenario is preferred on the basis of ex-
isting gravity data. A model is suggested in which this oceanic unit is part of the
allochthonous boninite-tholeiite stack overlying the Western Tasmanian Terrane.

Item Type: Thesis - Honours
Authors/Creators:Lorimer, T
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