Upper mantle anisotropic structure across the Blanco transform

Abstract:

Detailed knowledge of the seismic structure, fabric, and dynamics of the oceanic mantle continue to be refined through offshore seismic studies. Of particular interest is the nature of anisotropy surrounding the lithosphere-asthenosphere boundary. Previous high-resolution studies in the Pacific basin far from plate boundaries show asthenospheric fabric that aligns neither with the lithospheric fabric (the paleo-spreading direction) nor with absolute plate motion, but rather in between. Here we present preliminary results from the Blanco Transform and Cascadia Initiative experiments, investigating the structure of the Juan de Fuca and Pacific plates on either side of the Blanco Transform. We measure ambient-noise and teleseismic Rayleigh-wave phase velocities, and solve for the period-dependent azimuthal anisotropy on either side of the transform. We contextualize and interpret the fabrics based on mantle flow inferred from these previous Pacific basin studies.