Regional Sn velocities and shear velocity in the upper mantle

Determinations by various authors of the apparent velocity of the seismic shear wave Sn, which propagates in the uppermost mantle, are presented for several of the Earth's stable regions. Measurements of the velocity over two additional shield areas, India and Western Australia, were made and gave values of 4.72±0.03 km/sec and 4.75-4.87 km/sec, respectively. In general, the Sn velocity is greater than 4.7 km/sec. As the stable regions cover most of the Earth's surface and this velocity is representative of the shear velocity in the uppermost mantle, it is useful as a constraint in inversion of seismic data to determine upper-mantle structure.