Detecting seismic anisotropy above the 410 km discontinuity using reflection coefficients of underside reflections

摘要

We investigate the effect of various types of deformation mechanisms on the reflection coefficients of P and S waves underside reflections off the 410 km discontinuity, to develop a diagnostic tool to detect the style of deformation at boundary layers. We calculate the reflection coefficient for P and SH underside reflections using velocity perturbations resulting from aligned minerals above the 410 km discontinuity for different deformation scenarios. The results show that in the case of an anisotropic olivine layer above an isotropic wadsleyite layer, the P wave reflection coefficient amplitudes are only slightly influenced by the joint effect of angle of incidence and the strength of imposed deformation, without any polarity reversal and for all deformation styles. For the SH wave underside reflections the incidence angle for which a polarity reversal occurs, changes with distance for all scenarios and in addition changes with azimuth for shear deformation scenarios. These differences in amplitude and polarity patterns of reflection coefficients of different deformation geometries, especially for S wave at shorter distances potentially provide a possibility to distinguish between different styles of deformation at a boundary layer. We also show a first test using currently available elastic constants of anisotropic wadsleyite beneath anisotropic olivine.