Geophysical investigations of the south-western Wairarapa region of New Zealand

Abstract

A model of the sub-surface structure of the south-western part of the Wairarapa sedimentary basin in central New Zealand was constructed from geophysical data obtained by the author during the period 1990-1991. A total of 122 new gravity observations, eight magnetotelluric (MT) stations and approximately two kilometres of seismic refraction lines were established in the study area. All methods complemented each other in the determination of the final result. The gravity data provided the depth for the basement layer of the basin, and determined the position of a fossil fault in the region of the Wharepapa River channel. The MT and seismic data confirmed the fossil nature of the fault. The results for the boundaries determined by the MT surveys were also shown to agree with the upper layers of the gravity model. The final model presented is of a sedimentary basin with thickness of approximately 2km, with a fossil fault dividing the basin near the vicinity of the Wharepapa River. To the west of the study area is a highly anomalous region which could not be fully modelled in this study because of lack of data in this particular area.