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Title: Seismic scattering from small-scale heterogeneity
Author: Hulme, T.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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This dissertation is concerned with the scattering of waves by features which are on a sub-wavelength length scale. Although these features cannot be easily resolved, they may still cause significant wave scattering, and the general problem is to understand the situations under which this occurs, and the effects that it may have. A specific example of this generic problem is given by considering seismic wave propagation through sedimentary sequences. Channelisation in such sequences causes lateral variation on a length scale (5-30 m) that is comparable to, or smaller than, typical wavelengths used in seismic exploration. The effects of this variation on wave propagation are investigated using a combination of numerical modelling and experimental work. The Mount Messenger formation in North Taranaki, New Zealand is taken as a prototype sedimentary sequence. This sequence provides a superb exposure of slightly dipping turbidites and has been the subject of previous detailed outcrop studies. Field observations taken from this sequence have been used to build well-constrained, albeit simplified, models of typical channel and other sub-wavelength features. The elastic wave equation is solved for these models using new methodology, which reformulates the classical partial differential boundary value problem as a set of two first order initial value problems. A spectral expansion means that these initial value problems become ordinary differential equations, which can then be solved to a very high degree of precision. The resulting synthetic seismograms show that the sub-wavelength geometrical formations cause significant wave scattering, and that this scattering can introduce artefacts after simple processing steps. A high-resolution seismic reflection experiment has been carried out on the Mount Messenger formation, and processed sections from this experiment display features which can be interpreted as being analogous to the artefacts seen in the synthetic results.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available