Seismic Azimuthal Anisotropy Within the Juan de Fuca - Gorda Plate System

Abstract

We estimate seismic azimuthal anisotropy for the Juan de Fuca - Gorda plates from inversion of a new 10–80 s period Rayleigh wave dataset, resulting in a two-layer model to 80 km depth. In the lithosphere, most anisotropy patterns reflect the kinematics of plate formation, as approximated from seafloor-age-based paleo-spreading, except for regions close to propagator wakes and near plate boundaries. In the asthenosphere, the fast propagation orientations align with convective shear as inferred from the NUVEL1A plate motion model, which is indicative of a ∼3 Myr average, rather than with the more recent, ∼0.8 Myr, motions inferred from MORVEL. Regional anisotropy of this young plate system thus records convection like older plates such as the Pacific. On smaller scales, anisotropy imaging provides insights into dynamics of plate generation and can further elucidate plate reorganizations and changes in boundary loading.