Geodetic constraints on the kinematics of the Alpine Fault in the southern South Island of New Zealand, using results from the Hawea‐Haast GPS Transect

Abstract

Repeated GPS measurements at 21 sites along a profile extending 100 km southeast of the Alpine Fault demonstrate that active deformation occurs across much of the South Island of New Zealand and that slip on the Alpine Fault cannot accommodate all of the Pacific‐Australian plate motion. Projecting the velocity field as normal and parallel components to the Alpine Fault, shows that the fault‐parallel component of motion falls on a characteristic dislocation curve that suggests elastic strain accumulation in the upper crust. This type of deformation is associated with deep aseismic slip in the ductile regions below the brittle‐ductile transition. The derived slip rate, of greater than 20 mm/yr, is in reasonable agreement with geological observations. The best fitting locking depth is about 10 km. There is also evidence that approximately 25% of the relative plate motion is accommodated either by distributed deformation or by slip on a second structure located within the Southern Alps, approximately 80 km east of the Alpine Fault.