Western U.S. seismic anisotropy revealing complex mantle dynamics

- We quantify the origin of peculiar patterns of SKS splitting in the western U.S. using geodynamic models.
- Reproducing the key SKS features requires contributions from all major mantle seismic structures.
- Both lithospheric thickness variations and toroidal flows around the Juan de Fuca slab modulate mantle anisotropy locally.
- The ancient Farallon slab below the east coast affects the western U.S. by pulling its upper mantle eastward.
- The prominent E-W oriented anisotropy within the Pacific Northwest reflects landward intrusion of the hot Pacific mantle.