Lowermost mantle shear velocity anisotropy beneath Siberia

A study was conducted to analyze the lowermost mantle shear velocity anisotropy beneath Siberia by using the events in Japan and the records of Germany Regional Seismic Array Network (GRSN) and employing the travel times differences between ScS and S. Simple waveforms with stable radiation pattern of SH, high signal noise ratios, and clear peaks of SH and SV were selected from masses of records. Results of the study demonstrated that the SV is faster than SH, which is caused by the horizontal transverse isotropy (HTI). The observations showed that the seismic wave propagated along E-W direction, which illustrates that the geometry structure beneath Siberia has a symmetry axis to N-S direction. The study concluded that the HTI, which is the dominant structure beneath Siberia, has two possible mechanisms, including the lattice preferred orientation (LPO) of anisotropic materials and shape-preferred orientation (SPO) of material caused by strong upwelling from core mantle boundary (CMB).