- © 2008 by the Seismological Society of America
The active tectonics of New Zealand are dominated by three main features (figure 1). Beneath the North Island there is active subduction of the Hikurangi trough where the Pacific plate is undergoing oblique subduction beneath the Australian plate at ∼ 45 mm/yr (e.g., Demets et al. 1990; Demets et al. 1994). The Hikurangi trough extends from the Kermadec trench in the north and terminates in the upper South Island. Large subduction zone earthquakes of around Mw 8.0 in the lower North Island and around Mw 6.9 farther north are expected (Reyners 1998). Slow slip events have also been observed on the Hikurangi subduction interface (e.g., Wallace and Beavan 2006) similar to those documented at other Pacific Rim subduction margins (e.g., Dragert et al. 2001; Obara et al. 2004; Larson et al. 2004). A number of dextral strike-slip faults are also present throughout the North Island and the upper South Island and have produced a number of M 6.0–7.5 earthquakes in the past century (Doser and Webb 2003). The Wellington region is cut by five active dextral faults that have average recurrence intervals of meter-scale surface rupture that range from ∼ 500 to 5,000 years (Van Dissen and Berryman 1996). The Wairarapa fault is the only one of these to have ruptured in historic times, in 1855, in an event estimated at Mw 8.2 (Darby and Beanland 1992).