Shear wave splitting and waveform complexity for lowermost mantle structures with low-velocity lamellae and transverse isotropy

Shear wave splitting and waveform complexity for lowermost mantle structures with low-velocity lamellae and transverse isotropy

[1] Shear waves that traverse the lowermost mantle exhibit polarization anomalies and waveform complexities that indicate the presence of complex velocity structure above the core-mantle boundary. Synthetic seismograms for horizontally and vertically polarized shear waves (SH and SV, respectively) are computed using the reflectivity method for structures with low-velocity sheets (‘‘lamellae’’),...

Lowermost mantle flow at the eastern edge of the African Large Low Shear Velocity Province

Azimuthal anisotropy in the D00 layer beneath the Caribbean

[1] The lowermost mantle beneath Central America has anisotropic seismic velocity structure manifested in shear wave splitting of signals from South American earthquakes recorded at North American broadband recording stations. Prior studies of deep mantle anisotropy in this region have characterized the structure as having vertical transverse isotropy (VTI), which is sufficient to explain a gen...

Spectra of mantle shear wave velocity structure

We applied the stochastic method of Gudmundsson, Davies & Clayton (1990) (which was applied to ISC P-wave data) to teleseismic ISC S-wave data to obtain an independent estimate of mantle structure. We inverted the variance of S-wave traveltime residuals of bundles of rays to obtain a description of the spectrum of lateral heterogeneity as a function of depth through the mantle. The technique yi...

An SH hybrid method and shear velocity structures in the lowermost mantle beneath the central Pacific and South Atlantic Oceans

[1] An SH hybrid method is developed for calculating synthetic seismograms involving twodimensional localized heterogeneous structures. The hybrid method is a combination of analytic and numerical methods, with the numerical method (finite difference) applied in the heterogeneous region only and analytical methods applied outside the region. Generalized ray theory solutions from a seismic sourc...