Robert Stoneley and core-mantle boundary Stoneley modes

by Becky Coombs

Robert Stoneley FRS (1894-1976) was a Fellow of Pembroke College from 1943 until his death in 1976. He made many important contributions to geophysics, focusing mainly on surface waves, the most destructive seismic waves during an earthquake. The amplitude of these waves decays away from the surface, leaving them ‘trapped on the surface’. One of his first contributions was the theoretical prediction of similar waves trapped at interfaces within the Earth; these interface waves are called ‘Stoneley’ waves in his honour.

Similar to travelling waves being trapped at an interface, whole Earth free oscillations can also be trapped at a solid-liquid interface; so called ‘Stoneley’ modes. The core-mantle boundary (CMB), the interface between the solid silicate mantle and liquid outer core, is such an interface where these modes can occur, but these CMB ‘Stoneley’ modes had so far not been observed.

Motivated by Stoneley’s earlier work, current Pembroke graduate student Paula Koelemeijer and Pembroke Fellow Dr Arwen Deuss made the first robust observations of CMB Stoneley modes, made possible by the increased availability of seismic data for large earthquakes, including the 2004 Sumatra and 2011 Japan events. These new observations will help to constrain possible seismic structures in the Earth’s deep mantle.

The results were published in Geophysical Research Letters: P. Koelemeijer, A. Deuss and J. Ritsema (2013). Observations of Core-Mantle Boundary Stoneley modes, Geophysical Research Letters, Vol. 40(11), 2557-2561, doi: 10.1002/grl.50514. An abstract of the study can be found on the website.

http://onlinelibrary.wiley.com/doi/10.1002/grl.50514/abstract

Photo: Robert Stoneley by Walter Bird.