Seismic anisotropy in southern Costa Rica confirms upper mantle flow from the Pacific to the Caribbean.
Vadim Levin, Stephen Elkington, James Bourke, Ivonne Arroyo, and Lepolt Linkimer
We derive new constraints on the nature of seismic anisotropy in the upper mantle of southern Costa Rica from observations of birefringence in teleseismic shear waves. Fast and slow components separate by ~ 1 s, with faster waves polarized along the 40°-50° NE direction, near-orthogonally to the Central American convergent margin. Our results are consistent with the upper mantle flow from the Pacific to the Caribbean and require an opening in the lithosphere subducting under the region.
Observations of averaged shear wave splitting for all locations, with labels. Average splitting parameters (blue) and predictions of these parameters from a fit to the splitting intensity values (red). Bars are aligned with fast directions and scaled with delay values. Two active volcanoes flanking the study region where volcanism is presently absent are labeled.