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Title: Geophysical Inverse Modelling of the Internal Structure of the Sun and the Earth
Author: Cobden, Laura Jacqueline
ISNI:       0000 0004 2681 0810
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2008
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Seismology is arguably the most powerful technique for probing the interior of planetary bodies. On the Sun, this is a relatively new field (helioseismology), in which cross-correlation is used to extract coherent signals from random seismic noise. Here, I test the validity of the cross-correlation technique. The structure of the cross-correlated signal is only marginally different from the uncorrelated signal of a single source. However, large amounts of data must be averaged in order to produce a clear signal. A comparison of travel-time tomography utilising the cross-correlation approach, with wave field tomography, which need not require cross-correlation of data, indicates that structures can be imaged to higher resolution - both spatially and quantitatively - using the latter approach. On the Earth, extensive seismic imaging has already been done, and we move towards interpretation of seismic structure in terms of temperature and composition. Deviations from a radially-symmetric spherical structure amount to only a few percent. However, even for this background structure, thermochemical interpretation is debated. Here, I test, for the mantle between 250 and 2500 km depth, the compatibility of potential 1-D thermochemical structures, with a range of seismic data. Furthermore, I account for the large uncertainties in the conversion from thermo-chemical to seismic structure, using a thermodynamic approach that determines phase relations, elastic parameters, density and anelasticity. In the upper mantle, the data require significant change in average chemical composition with depth, most likely due to 3-D chemical heterogeneity, especially around 660 km. In the lower mantle, clarification of the values of temperature and pressure derivatives of the mineral elastic moduli would be necessary to constrain tightly the average thermochemical structure. A superadiabatic temperature gradient, plus a change in composition with depth, may provide a better fit to the data than the commonly-assumed homogeneous, adiabatic pyrolite profile.
Supervisor: Goes, Saskia ; Warner, Mike Sponsor: Janet Watson Scholarship
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available