The Pukaki microearthquake network has revealed significant earthquake activity deeper than 15 km in the central South Island, New Zealand, extending to a depth of 73 km beneath the crest of the Southern Alps. Events deeper than 25 km define a planar seismic zone that has a strike of 41° and dips northwest at 19°. Gravity models suggest that earthquakes in this zone are occurring in a seismogenic uppermost mantle underlying an aseismic lower crustal root to the Southern Alps. The 17° difference in strike of the dipping seismic zone and the Alpine fault provides an explanation for the pattern of uplift and crustal thickening seen in the central South Island.

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