SKS SPLITTING AND THE SEISMIC ANISOTROPY OF THE MANTLE BENEATH THE HIKURANGI SUBDUCTION ZONE, NEW-ZEALAND

The analysis of 12 SKS phases recorded on broadband stations above the Hikurangi subduction zone in New Zealand shows clear evidence of mant le anisotropy, with the fast direction (28 degrees +/- 5 degrees) almo st parallel to the strike of subduction and the dominant geology of th e region. The slow shear-wave delay times show a systematic change wit h the azimuth of the arrivals which, if hexagonal symmetry is assumed, indicates that either the axis of symmetry of the anisotropic volume beneath the subduction zone is not horizontal, or that more than one a nisotropic layer is present. The magnitude of the delays (1.5 +/- 0.4s ) suggests that the anisotropy is most probably confined to the top 30 0 km of the mantle.