Geophysics, Geodynamics and Tectonics.
My research has focused on the structure and mechanical behaviour of the continents. This work uses seismology to image the internal structure of the Earth, and the resulting images can then be used to test hypotheses of the Earth's evolution and dynamics. I combine my seismic results with advances in geochemistry, petrology, and mineral physics to relate the measured seismic wave speeds to temperature and composition and to progress past a simple description of the seismic structure to an understanding of more fundamental processes that have shaped the Earth during its evolution.
My recently-completed analysis of about four million regional surface wave seismograms has now enabled me to build upper mantle models for all continents and oceans with a horizontal resolution of a few hundred kilometres and a vertical resolution of about 30 kilometres. In collaboration with Dan McKenzie, I have developed a relation between upper mantle shear wave velocity and temperature which has allowed me to produce the first thickness maps of the lithosphere, the cold boundary layer near the Earth's surface which controls the Earth's heat loss and the tectonics of the oceans and continents. These lithospheric maps show how extensive regions of thick lithosphere have controlled the geometry of continental deformation and have provided significant new insights on the formation and evolution of the continents.