Seismic anisotropy of subducting oceanic uppermost mantle from fossil spreading

Abstract

Identifying the sources of seismic anisotropy in subduction zone forearcs is key to understanding mantle deformation processes. Current models based on the interpretation of shear-wave splitting measurements favor the flowinduced alignment of olivine crystals around down-going slabs or the presence of foliated serpentine minerals due to subduction-related processes, thereby neglecting fossil slab fabric as a significant source of anisotropy. We use seismic receiver functions to show evidence for strong anisotropy within anhydrous uppermost mantle of subducting oceanic plates in the forearcs of Nankai, Cascadia, Mexico, and Costa Rica subduction zones. Seismic anisotropy models from the inversion of receiver function waveforms are consistent with fossil fabric generated at spreading ridges. © 2013. American Geophysical Union. All Rights Reserved.