11:00 〜 11:15
[SIT20-20] 沈み込みスラブと最下部マントル物質の相互作用：波形インバージョンによる中米下の鉛直軸対象異方性構造からの洞察
キーワード：波形インバージョン、最下部マントル、異方性、D″、沈み込みスラブ
The D″ region is the thermal boundary layer (TBL) of mantle convection located in the lowermost few hundred kilometers of the Earth’s mantle, playing a crucial role in mantle dynamics. The cold and chemically distinct subducted slabs, the descending flows of mantle dynamics, are thought to interact with the hot TBL materials. Therefore, the D″ region, especially beneath the subduction zones, is important to understand the Earth’s thermal and chemical evolution.
To estimate the behavior of the subducted slabs in the D″ region, we apply the waveform inversion to the transverse and radial component seismograms mainly provided by USArray and infer the transversely isotropic (TI) S-velocity structure beneath Central America. Our preliminary model shows high-velocity anomalies beneath Central America, interpreted as the Farallon slab, and low-velocity anomalies from Colombia to the Caribbean Sea, interpreted as a passive plume. Our preliminary model also exhibits TI parameter (ξ) anomalies with higher resolution than previous models. In the regions corresponding to the Farallon slabs, we generally resolve high-ξ in most regions but low-ξ 200-100 km above the CMB. In the regions corresponding to a passive plume, we found low-ξ 400-200 km above the CMB and high-ξ 200-100 km above the CMB. Considering these ξ anomalies, we propose that subducted slabs descend not straight to the core-mantle boundary (CMB) but exhibit complex flow patterns by interacting with dense materials just above the CMB. We also suggest that the root of a passive upwelling plume is pushed eastward by subducted slabs. Our presentation will show the refined model and the results of validity tests.
To estimate the behavior of the subducted slabs in the D″ region, we apply the waveform inversion to the transverse and radial component seismograms mainly provided by USArray and infer the transversely isotropic (TI) S-velocity structure beneath Central America. Our preliminary model shows high-velocity anomalies beneath Central America, interpreted as the Farallon slab, and low-velocity anomalies from Colombia to the Caribbean Sea, interpreted as a passive plume. Our preliminary model also exhibits TI parameter (ξ) anomalies with higher resolution than previous models. In the regions corresponding to the Farallon slabs, we generally resolve high-ξ in most regions but low-ξ 200-100 km above the CMB. In the regions corresponding to a passive plume, we found low-ξ 400-200 km above the CMB and high-ξ 200-100 km above the CMB. Considering these ξ anomalies, we propose that subducted slabs descend not straight to the core-mantle boundary (CMB) but exhibit complex flow patterns by interacting with dense materials just above the CMB. We also suggest that the root of a passive upwelling plume is pushed eastward by subducted slabs. Our presentation will show the refined model and the results of validity tests.