Strain measurements and tectonics of New Zealand

Abstract

(Accepted for publication June 8, 1978) ABSTRACT: Measurements of shear strain from triangulation data have been made at 30 locations in New Zealand. The standard error of measurement in terms of strain rate is about +1 · 10 +7 y +1 and values of up to 7 · 10 +7 y +1 are observed. Together with 22 fault-plane solutions for crustal earthquakes the measurements indicate broad-scale patterns of deformation. Between the Hikurangi and Flordland active margins is a 100-km-wide belt, the axial tectonic belt, with shear strain rate averaging 5 + 1 · 10 +7 y +1 and an azimuth of the principal axis of compression of 114 + 8°. The rate of movement (45 mm y +1 ) and direction (085°) between the Pacific and Indian plates from the Minster et al. pole can be accounted for by the measured strain in the axial tectonic belt through simple shear parallel to, and compression normal to, the belt. The similarity in the rates determined from triangulation data averaged over 20-100 years and from plate movement averaged over 5 m.y. indicates plate movement to be uniform in time. West of the axial tectonic belt in Nelson and Fiordland are two zones in which movement is highly oblique to plate movement, and can be explained by slip line deformation analogous to the deformation of Asia. The azimuth of the principal axis of compression in the Taupo rift and East Cape region is NE—SW, perpendicular to its direction in the axial tectonic belt, suggesting extension in the rift and East Cape region normal to the subduction zone.