Dr Stewart Fishwick

Seismic Structure of the Upper Mantle

My main research interest is understanding the variations in seismic wavespeed within the upper mantle.  Can we link the observed velocities to large scale tectonic processes and the geology observed at the surface, and how are the variations related to changes in the physical properties of the lithosphere and asthenosphere?  Research has been focussed on continental scale studies (Australia and Africa), however, I believe that incorporating data at various length-scale is an important challenge, and will lead to an improved understanding of the structure of the Earth.

Surface wave tomography is an ideal tool for investigating the upper mantle and my work has focussed on looking at ways to improve the reliability of the tomographic models.  Multiple starting models can be used in the inversion process to get a better estimate on the reliability and uncertainty related to the data. One of the problems with tomographic images is that what is observed is strongly dependent on the colour scale and reference model, for this reason I have also looked at using images of the horizontal gradient to define where there are rapid variations in wavespeed (link).

The focus of my present research is the relationship between the tomographic models and physical processes within the Earth:

• The results from a number of tomographic studies in cratonic regions suggest a positive velocity gradient in the upper mantle, which is not compatible with simple physically based models of constant composition and cratonic geotherms.  Investigating the internal structure of the lithospheric mantle is a major target and the subject of a NERC New Investigator proposal.
  
• Beneath Africa there is a long-standing interest in the relationship between mantle convection, volcanism, and topography. Using the results from my recent tomographic study this has become an area of focus for my research, with collaborations with Dr Nicky White (University of Cambridge), and as an international collaborator on a recent proposal by a group at the University of Rennes.