Experimental Determination of the Effect of Dislocations on Shear Anelasticity in Olivine at Seismic Frequencies and High Temperature

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The ultimate aim of this work is the understanding of the rheology of the mantle and the conditions there which are responsible for plate motion. The movement of tectonic plates must be accommodated by flow in Earth's mantle. This flow occurs in the solid state and in turn must be accommodated by the motion of defects within crystals and along grain boundaries. As seismic strain waves traverse the mantle they interact with these defects which results in attenuations. This study is aimed at gaining an understanding of the interaction of seismic waves with defects in single crystals of mantle minerals. An experimental apparatus has been developed to measure the attenuation of strain waves at seismic strains and frequencies and under mantle conditions of temperature and chemical environment. Olivine has been chosen as the first minerals to be studied because of its proposed abundance in the mantle and because it is quite deformable under mantle conditions. The state of stress in Earth's mantle is probably the major factor controlling the defect structure there. An understanding of that structure, gained through the comparison of laboratory attenuation measurements with seismic data, should eventually yield stress mapping of Earth's mantle.