Velocity and Anisotropy Structures and Thermal and Compositional Models Beneath Eastern Asia and North America

The upper mantle velocity and anisotropy structures are important to the understanding of mantle composition and dynamics. We constrain fine seismic SH and SV velocity and anisotropy profiles in the upper mantle beneath eastern Asia and North America, and explore mineralogical and compositional models and crystal alignments based on mineral physics modeling. We use the triplicated phases recorded in the epicentral distance range of 13°- 40° for events occurring in eastern Asia and North America to constrain the SH and SV velocity models in the upper mantle beneath the two regions. Directly comparing the SH and SV data in the triplication distance range provides information of anisotropy changing with depth. For an eastern Asia event, SH waves arrive at the same time as SV waves for those traveling in the transition zone, but earlier than SV waves for those traveling below the 660-km discontinuity. Such observations indicate two possibilities: 1) the upper mantle in this region is isotropic and the uppermost lower mantle is anisotropic with an SH velocity larger than the SV velocity; and 2) these shear wave splitting difference may indicate existence of lateral variation of lithosphere anisotropy. In joint modeling of the mineral physics and seismic data, we explore a variety of compositional and thermal models and crystal alignments by comparing their predicted velocity and anisotropy profiles using the mineral physics modeling with the seismic velocity and anisotropy structures inferred from the seismic data. We will present best-fitting thermal and compositional models and the crystal alignments with their predicted velocity and anisotropy structure best explaining the seismic data.