Global transition zone tomography

摘要: [1] Our understanding of large-scale mantle dynamics depends on accurate models seismic velocity variation in the upper transition zone (400–1000 km depth). With Mode Branch Stripping technique (MBS) van Heijst and Woodhouse [1997] it is possible to extract dispersion characteristics overtone surface wave signals from single source-receiver waveforms. Such data provide new global constraints. We combined more than a million measurements path-average phase with normal-mode splitting functions body travel times construct model S20RTSb shear heterogeneity throughout mantle. discuss detail resolution structural zone. The main observations are following: (1) Large-scale variations (15%) 250 at least 5 larger deeper High-velocity keels Archean cratons extend about 200 depth. Low velocities related mid-ocean ridge upwelling confined 150 (2) 220-km discontinuity PREM cannot be reconciled Rayleigh dispersion, especially oceans. (3) below oceanic lithosphere (350–400 depth) 1–1.5% lower beneath continental lithosphere. (4) slabs former conspicuous structures just above 670-km discontinuity. They 1100 depth South American, Indonesian, Kermadec subduction zones, indicating that penetrate through several zones. (5) observe lower-than-average eight hot spots (including Hawaii, Iceland, Easter, Afar). It is, however, difficult accurately estimate their extent because limited vertical resolution.