Theoretical Geophysics in the UK

The Earth we inhabit is a beautiful and exciting place. It provides the air we breathe; the water we drink; the coal we burn to warm us; the oil we use for transport; precious minerals for our social benefit and for industrial usage; and maintains a magnetic field to protect us from cosmic radiation.

Theoretical geophysics uses concepts in physics along with quantitative arguments to understand the workings of the Earth and its environment. The sub-disciplines include at least the main topics of seismology, tectonics and geomagnetism, along with subsidiary areas such as the measurement of gravity and its variation with position on the surface of the Earth, the study of electromagnetic currents induced within the Earth and the evaluation of the heat flow from radioactive sources and original hot regions from deep within the Earth.

In addition, areas which have only recently been absorbed into theoretical geophysics include the study of the oceans and atmospheres: oceanography and meteorology and most importantly, their interactions. These have important consequences on our future and past climate.

Seismology, initiated just over a hundred years ago, at approximately the same time as the study of X-rays to investigate humans, is the study of waves propagating throughout the Earth whose mean radius is 6378 km. By accurately measuring the travel time of these waves much can be learnt about the structure of the interior of the Earth through which they propagate. Thus we know that there is a solid inner core of 1221 km radius enveloped by a liquid outer core to a radius 3488 km beyond which is the mainly, but definitely not entirely, solid mantle with a thin crust of relatively brittle material.

Tectonics is the study of the major structural and deformational features in the outer part of the Earth, including the form of the continents, the ocean floor, mountain building and the formation of faults. This area led in the early 1960s to a revolution in the Earth sciences with the introduction of plate tectonics, whereby the lithosphere comprising the crust and solidified upper most part of the mantle is broken up into seven major tectonic plates and a number of minor ones. These plates are in continual, virtually rigid motion relative to each other at the rate of between 1 to 10 cm/year – about as fast as your fingernails grow. Their proposal led to unifying many different diverse geological phenomena.

Geomagnetism uses data, some collected over 300 years ago, to motivate studies of the unsteady motion in the iron-rich, liquid outer core which maintains the Earth’s magnetic field, in a way that is not yet thoroughly understood.

The discipline of fluid mechanics is playing an ever increasing role in theoretical geophysics. Its importance in geomagnetism, oceanography and meteorology is obvious, but as well it plays an essential role in the migration of melt from sources in the mantle to the crust where it tends to pond in large magma chambers, or storage reservoirs of partially molten rock, beneath volcanoes. These chambers act as the powerhouse for any subsequent volcanic eruptions. The UK is at the forefront in the development of this area, with powerful groups at both Bristol and Cambridge universities.

Neighbouring subdisciplines of theoretical geophysics include geochemistry, atmospheric chemistry and chemical oceanography, all of which use chemical techniques to study the Earth rather than the physical techniques of geophysics.

The study of theoretical geophysics can lead to a stimulating and exciting career in either academia or industry. Both oil and mining companies are always on the lookout for bright, capable geophysicists. Additional areas include seismic verification of nuclear test bans, investigation of nuclear waste disposal and hydrogeology, or groundwater modelling.

The subject has always been strong in the United Kingdom. The great names have included Sir Harold Jeffries, Sir Edward Bullard, Sir Geoffrey Taylor, Professor Dan McKenzie CH, all Professors in the University of Cambridge, which still contains the biggest and best department of Earth sciences in Britain.

Thanks to: Herbert E Huppert

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