Faults in Cook Strait and their bearing on the structure of central New Zealand

Abstract

Seismic reflection data reveal that the major dextral transcurrent faults of the North and South Islands, with the possible exception of the Wairau Fault, do not link directly across Cook Strait. Off Marlborough, the extension of the Wairau Fault is a series of northeast-trending fractures, one of which runs west of Kapiti Island towards the mouth of the Rangitikei River. En route, the Wairau Fault defines the western margins of the prominent Wairau and Narrows sedimentary basins. The southeastern edge of the Wairau Basin is the Awatere Fault which bends sharply to the east to merge with the steep topography of Cook S trait Canyon. The neighbouring Hog Swamp Fault follows a similar trend. The Clarence Fault has not been identified offshore whereas the Kekerengu and Hope Faults can be traced only a few kilometres beyond the coast. On the Wellington side of Cook Strait, the offshore extensions of the Ohariu and Wellington Faults terminate in the thick sedimentary pile of the Wairau Basin. Further along the coast, the West Wairarapa Fault extends to Cook Strait Canyon where it appears to be offset dextrally, the southerly continuation extending to the Marlborough continental shelf. Faults from both islands terminate in the central strait along an apparent dextral offset. This is attributed to the clockwise rotation and dislocation of the fault belt in response to differential movement between the Indo-Australian and Pacific plates in late Cenozoic times.