Geodetic constraints on the kinematics of the Alpine Fault in the southernSouth Island of New Zealand, using results from the Hawea-Haast GPS transect

Repeated GPS measurements at 21 sites along a profile extending 100 km sout heast 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 t he velocity field as normal and parallel components to the Alpine Fault, sh ows that the Fault-parallel component of motion falls on a characteristic d islocation curve that suggests elastic strain accumulation in the upper cru st. This type of deformation is associated with deep aseismic slip in the d uctile regions below the brittle-ductile transition. The derived slip rate: of greater than 20 mm/yr, is in reasonable agreement with geological obser vations. The best fitting locking depth is about 10 km. There is also evide nce that approximately 25% of the relative plate motion is accommodated eit her by distributed deformation or by slip on a second structure located wit hin the Southern Alps, approximately 80 km east of the Alpine Fault.