[S-IT14] Deep Earth Sciences

[SIT14-12] Inferring 3-D azimuthally anisotropic structure of the lowermost mantle beneath the Northern Pacific using waveform inversion

*Ikuchi Funahashi¹, Kenji Kawai¹ (1.University of Tokyo)

Keywords:lowermost mantle, seismic anisotropy, waveform inversion

Seismic anisotropy is relevant to subsurface deformation and flow. Especially for the lowermost mantle, which plays an essential role in mantle dynamics, it is one of the few sources of information. However, the constraint on the strain state imposed by previous studies is limited because of the paucity of estimated parameters. Waveform inversion is a method that can infer azimuthally anisotropic structure with more than three parameters, thanks to the abundance of available data and the simplicity of introducing anisotropic parameters. This study uses 33,599 three-component broadband body-wave seismograms and performs waveform inversion for the three-dimensional azimuthal anisotropy structure of the lowermost mantle beneath the Northern Pacific. We introduce a Bayesian model to the inversion process, enabling validity comparison among models with different anisotropy. As a result, the model with azimuthal anisotropy was preferred in the comparison. The model tightens the constraints on the orientation of the mineral crystals that produce the anisotropy in the high-velocity area, which is thought to be the remnant of the Izanagi Plate; in the case of Bridgmanite, flow in the north-south direction is the most plausible explanation. This presentation will focus on the model evaluation using a Bayesian model and the geophysical interpretation of the resulting model.