Subcrustal earthquakes beneath New Zealand; Locations determined with a laterally inhomogeneous velocity model

Abstract

Inconsistencies have become apparent in locations allocated to subcrustal earthquakes beneath the main seismic region of New Zealand. To reduce these, a simple model has been set up in which velocities are increased along ray paths presumed to be entirely in the zone of deep earthquakes. The results are most consistent when the velocities of both P and S waves are increased by 11%, compared with the standard Jeffreys-Bullen model. The effect of this velocity change is to reduce the dip of the zone of subcrustal foci determined in previous studies, and to make the foci more closely planar. The newly defined plane strikes N 45° E and dips at 50° to the north-west.