S U M M A R Y Concerns over the validity of expressions derived by Montagner et al. that link SKS splitting measurements to the variation with depth of anisotropic parameters in the upper mantle have been recently expressed, pointing out that the long period approximations applied by these authors may not be valid for the frequency range commonly used in SKS studies, and in particular, that the...

The Gulf of California region has undergone a major evolution over the past ∼15Ma, since subduction of the now-extinct Farallon plate ceased and transform motion began, leading to the initiation of rifting and the opening of the Gulf of California ∼5Ma ago. The character of dynamic processes in the upper mantle beneath the region remains poorly understood, but constraints on seismic anisotropy ...

Shear wave splitting of SK(K)S phases is often used to examine upper mantle anisotropy. In specific cases, however, splitting of these phases may reflect anisotropy in the lowermost mantle. Here we present SKS and SKKS splitting measurements for 233 event-station pairs at 34 seismic stations that sample D′′ beneath Africa. Of these, 36 pairs show significantly different splitting between the tw...

INTRODUCTION SUMMARY We have determined the shear wave splitting parameters for a dense network of broad-band stations in the western United States using high-quality SKS and SKKS waveforms, with par~ ticularly high spatial resolution in the southern California region covered by the TriNet seismic network. The alignment of most fast polarization directions can be explained by plate-tectonic, ex...