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Matthew Maitra

Matthew  Maitra

Research Student

Long period free-oscillations of the Earth

Geophysics, Geodynamics and Tectonics

Bullard Labs.
Madingley Rise, Madingley Road
Cambridge
CB3 0EZ

Office Phone: +44 (0) 1223 333493

Research Interests

Free-oscillations provide one of the most important constraints on the Earth's internal structure at long wavelengths. Indeed, free-oscillation periods were the main data used in determining the Earth's spherically symmetric density structure, while free-oscillation spectra can be used to image lateral density variations in the mantle. This latter point is of particular relevance to the question of whether convection within the lowermost mantle is driven by thermal or compositional buoyancy.

The free-oscillations of an Earth model that is entirely solid, perfectly elastic and utterly unrealistic are well understood. The difficulty (and interest) comes from the inclusion of inviscid fluid regions -- such as the outer core and oceans -- which fundamentally changes the nature of the eigenvalue problem associated with free-oscillations. The elastodynamic operator loses the usual Fredholm property, leading to the existence of an essential spectrum near zero frequency the precise nature of which is not yet understood. In previous work it has been argued, without full proof, that this part of the spectrum is continuous and that observable long period free-oscillations such as the free core nutations are embedded therein. If this is true, there are significant complications related to computation and excitation of these oscillations.

Furthermore, the effects of a finite viscosity or viscoelasticity at these long periods have also received little attention, and are of particular relevance to dynamic interactions of the core and mantle. At these long periods, however, the dynamics of the Earth are greatly complicated by the Earth's rotation, the nature of the density stratification within the outer core, viscous or viscoelastic dissipation, and possible interactions with the Earth's magnetic field.

The aim of my PhD is to develop new theoretical and computational approaches to study the longest period free-oscillations of the Earth, from periods of about an hour to about a year; the project is therefore strongly applicable to the study of Earth structure. We also hope that our work could be used to explore the dynamics of planetary systems. A particular area of interest is exoplanetology, a field notorious for its paucity of data. We hope that detailed study of the relationship between, say, internal density structure and orbital evolution will permit a greater quantity of information to be extracted from the available data.

Research Supervision

Supervisors: David Al-Attar, Sanne Cottaar

Keywords

Geophysics ; Geodesy ; Seismology

Key Publications

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