Lowermost mantle anisotropy along the boundary of the easternmost Pacific LLSVP

To evaluate the strength of D″ anisotropy beneath the easternmost Pacific Large Low Shear Velocity Province (LLSVP), SKS and SKKS splitting measurements were conducted separately. We examined SKS and SKKS phases for events (Tonga trench) over the life time of 5 seismic stations located in South America and Central America. These phases sample lowermost mantle of easternmost Pacific LLSVP. Finally, 22 SKS-SKKS phase-pairs were obtained, of which six pairs show significantly different splitting between the two phases. The results showed the existence of lowermost mantle anisotropy. We attempt to account for these observations with deformation along LLSVP boundary and small-scale lateral heterogeneity in anisotropic structures in LLSVP's interior, respectively. Based on previous observations, the absence of discrepant pairs clustering along the boundary of LLSVP indicates that the LLSVP boundary is not very sharp here and there is no strong deformation accumulated near the LLSVP boundary beneath the studied region. We also discussed the significance of the research on lowermost mantle anisotropy.