The influence of deformation history on the interpretation of seismic anisotropy

Abstract

Seismic anisotropy in the mantle is primarily caused by the lattice-preferred orientation (LPO) of olivine, which forms and evolves in response to progressive plastic deformation. The style of LPO and its rate of evolution depend on the effects of physiochemical conditions on the microphysics of deformation and recovery. Here, we integrate results from laboratory experiments and naturally deformed shear zones to evaluate how variability in the evolution of olivine LPO modifies existing strategies for interpreting seismic anisotropy. We concentrate on two particular effects. First, we show that olivine A- and E-type LPOs evolve with opposite senses of rotation, producing a wide spectrum of angular relationships between the orientation of fast seismic wave propagation and the direction of flow. Second, we show that the presence of a pre-existing LPO introduces a lag between changes in deformation kinematics and alignment of the seismic fast direction with the shear direction. The combination of these two factors affects the inference of deformation kinematics from seismic anisotropy and the interpretation of shear wave splitting parameters. Copyright © 2012 by the American Geophysical Union.