Deformation associated with the 18 June 1994 Arthur's Pass earthquake, New Zealand

Abstract

The 18 June 1994 Arthur's Pass earthquake (M_w . 6.7) occurred in the Southern Alps of New Zealand, within a network of global positioning system (GPS) stations first measured in 1992. Surface deformation caused by the earthquake was measured by resurveying the GPS network, revealing a maximum horizontal station displacement of c. 50 cm. An elastic dislocation model of a fault c. 40 km long, oriented NNW and dipping steeply to the west, produces a good fit to the GPS data. The fault model extends from the surface to 7 km depth and has up to 5 m of predominantly left‐lateral displacement. It strikes perpendicular to known major faults in the area, including the Alpine and Hope Faults to the north and the Porters Pass‐Amberley Fault Zone to the south. These larger mapped faults all display dextral strike‐slip offsets, whereas the fault that ruptured in the June earthquake had sinistral motion with a smaller component of reverse slip. Most of the moment release was concentrated in the hypocentral area, with less slip farther south. The location of the best fit dislocation model agrees with preliminary aftershock locations. The pattern of the first few days of aftershocks suggests that right‐lateral structures perpendicular to the main rupture were also activated during the earthquake or in the following days. There is some evidence for this fault complexity in the GPS data.