Whole mantle SH velocity model constrained by waveform inversion based on three-dimensional Born kernels

Abstract

SUMMARY A whole mantle SH velocity model is obtained by using a unique data set and techniques. Body and surface waveforms including major and multi‐orbit phases are used as a data set and are inverted by using 3‐D Born kernels. The resultant model, SH18CE, reveals the different natures of the two major upwelling systems: the strong low velocity anomalies beneath Africa extend for more than 1000 km from the core–mantle boundary (CMB), whereas those beneath the Pacific are restricted to 300–400 km from the CMB. The results also show the variable natures of stagnant slabs on the 670 discontinuity around Japan: the depths of the strongest high velocity anomalies within the stagnant slabs are different region by region, which is consistent with the detailed delay time tomography model in this area.

Origin of hotspots in the South Pacific: Recent advances in seismological and geochemical models

“…The low-velocity conduits ascend from broad low-velocity anomalies immediately above the CMB. Takeuchi (2007Takeuchi ( , 2009) obtained a similar image of the S-velocity structure from the waveform inversion of long-period transverse records (slower by 1.5-2%). On the other hand, some tomographic studies showed a large (700-1000 km in diameter), dome-like low-S-velocity anomaly (slower by 1.5-2%), occurring only in the lowermost mantle (Masters et al, 2000;Ritsema and van Heijst, 2000) or extending from the CMB to the middle-lower mantle (Figs.…”

Simulation of heterogeneity sections obtained by neutrino radiography

“…The regions are thus considered to have lower-density anomalies; this is also opposite of what would be expected from thermal anomalies. (Takeuchi, 2007), SAW24B16 (Mégnin and Romanowicz, 2000), SB4L18 (Masters et al, 2000), S20RTS (Ritsema et al, 1999), and S362D1 (Gu et al, 2001). The distance and direction from the center of the figure show the radius and the longitude of the central points, respectively.…”

“…I consider here the following 3D density model: (1) the low-velocity region beneath Africa has +10% density anomalies, (2) the region beneath East Antarctica has −10% density anomalies, and (Takeuchi, 2007), SAW24B16 (Mégnin and Romanowicz, 2000), SB4L18 (Masters et al, 2000), S20RTS (Ritsema et al, 1999), and S362D1 (Gu et al, 2001). The average of these five sections (labeled as AVERAGE) is also plotted.…”

“…I therefore focused on the longwavelength models. Since the simulated patterns might be biased by uncertainties in the tomography models used, I tested and compared the results of five models: SH18CE (Takeuchi, 2007), SAW24B16 (Mégnin and Romanowicz, 2000), SB4L18 (Masters et al, 2000), S20RTS (Ritsema et al, 1999), and S362D1 (Gu et al, 2001). All are S-velocity models obtained by using broadband waveform data.…”

“…Secondary data (such as body wave travel times, phase velocity of surface waves, and splitting functions of free oscillation modes) are frequently extracted from the waveforms and are inverted (e.g., Ritsema et al, 1999;Masters et al, 2000;Grand, 2002;Montelli et al, 2004). To fully exploit information included in the waveform data, a waveform inversion (e.g., Mégnin and Romanowicz, 2000;Panning and Romanowicz, 2006;Takeuchi, 2007) or a joint inversion of the secondary data and waveform data (e.g., Gu et al, 2001Gu et al, , 2003 is conducted. These procedures are strong in their ability to resolve the long-wavelength features of global lateral heterogeneities but are relatively weak in their ability to resolve fine structures.…”