Determination of SKS/SKKS-splitting parameters in the lowermost mantle beneath Siberia

The observation of shear wave splitting (SWS) is an unambiguous indication of seismic
anisotropy in the Earth’s interior and, thus, of deep geodynamic deformation processes.
The latter is based on the premise that crystals exhibiting anisotropic elastic properties
can be aligned or deformed by deformation processes or flows. This results in a directional
dependency of seismic velocities and therefore SWS.
In the Earth’s lowermost mantle (LMM), specifically in the D′′ layer, there exist large-scale
structures that drive global processes (mantle plumes) or result from them (remnants of
subducted slabs). These structures potentially influence the heat flow from the core and the
magnetic field lines through the mantle. In order to investigate the latter in particular, the
SWS of SKS, SKKS, and PKS (jointly referred to as XKS) phases propagating through a
high latitude flux lobe (HLFL), a region of higher magnetic flux, below Siberia is measured.
The splitting parameters, the fast polarisation direction ϕ and the delay time δt, are
determined using both the energy-minimisation and the rotation-correlation method in the
MATLAB program SplitLab. ... mehrA special focus lies on phase pair SWS discrepancies, i.e.,
between SKS and SKKS phases, as they are a clear indication for a LMM contribution to
the splitting signal.
Our study of the target region of Siberia has revealed anisotropy in this region and a
comprehensive image of this anisotropy has been obtained by studying the region along
different orientations of raypaths. A total of 49 pairs of core refracted phases have been
measured. Out of these, 19 pairs are discrepant. For these pairs, the phases with piercing
points in the region of the highest magnetic flux predominately show splitting, while we
observe mostly no splitting for phases piercing through the D′′ layer at larger offsets from
the HLFL.