The kinematics of active deformation in the North Island, New Zealand, determined from geological strain rates

Kinematic modelling utilising the method of Haines & Holt extended to the c ase of cubic Bessel interpolation on curvilinear grids, allows analysis of present-day horizontal motions occurring in the Hikurangi margin, North Isl and, New Zealand. The velocity field solutions are derived from first order geological data; that is, rates and orientation of extension in the Taupo Volcanic Zone and rates and orientation of motion on the North Island Dextr al Fault Belt, against the background of the pattern of uplift and subsiden ce in the margin. A basic (preferred) velocity field is presented, with four other solutions with different input data, to explain what controls features in the main so lution. Every one of the five solutions is the best fitting solution for th e input data in each case. All velocity fields are shown relative to the we stern boundary of the model, which is considered fixed, as part of the assu med non-deforming Australian plate. The velocity field in the main solution includes a strong clockwise rotatio n of the Hikurangi margin east of the Taupo Volcanic Zone in the north. Far ther south, shear across the North Island Dextral Fault Belt facilitates th e southwestward motion of the eastern part of the margin. An important boun dary condition for the deformation in the North Island appears to be the hi gher rate of dextral shear in the Marlborough region, which accommodates th e relative motion of the Australian and Pacific plates immediately south of the Hikurangi margin. The extension in the Taupo Volcanic Zone, with rates onshore of 5-10 mm/yr north of where the Taupo Volcanic Zone terminates in the centre of the Nort h Island, and the strike-slip component of shear on the North Island Dextra l Fault Belt, of c. 20 mm/yr in the south and <5 mm/yr in the north, accoun t for most of the margin-parallel plate motion in the Hikurangi margin. No other major geological strains are required to be occurring in the North Is land out of compatibility with these strains.