[SIT27-P03] P Velocity Heterogeneities in the Upper Mantle beneath the Northwestern Pacific
Keywords:seismology, mantle, lithosphere, asthenosphere
In this study, we investigated to reveal regional variations of P structures within the Northwestern Pacific. We defined two data bins so that the raypaths belonging to each bin sample similar regions with similar azimuths. The observed waveforms of each bin are coherent, which shows plausibility to compare obtained 1-D models. The preliminary results showed significant differences both in the lithosphere and the asthenosphere. The observed differences in the lithosphere (~4%) are consistent to the azimuthal anisotropy in the uppermost mantle reported by previous exploration studies. However, the differences in the asthenosphere (~2%) are unlikely to be explained by azimuthal anisotropy by olivine LPO because the angles to the plate motion direction are similar. This may suggest some mechanism to produce larger-scale (~1000 km) lateral heterogeneities in the asthenosphere.