An intermediate-depth earthquake in the Central Region of the South Island used to determine a local crustal thickness

Abstract

An earthquake has been located at a depth of 62 km near the junction of the Landsborough and Haast Valleys, in south Westland, New Zealand (43·99° S, 169·44° E). This is the first subcrustal earthquake to have been confirmed in the area, which is about 120 km north-east of the intermediate-depth earthquakes of the Fiordland Seismic Region. It was located about 50 km to the west of the recently installed telemetered seismograph network associated with the Upper Waitaki Power Project. The network recorded arrivals between the P and S phases, which have been identified as having been converted from S to P at the base of the crust. Analysis of these converted phases indicates a crustal thickness of 32 ± 1 km at the area of conversion, which is beneath Mount Huxley near 44·1° S, 169·7° E.