Coastal Restoration Trust of New Zealand

Coastal Dune Ecosystem Reference Database

1855 Wairarapa earthquake symposium: All-day field-trip to the Wairarapa Fault and 1855 rupture sites

Little, T.; Begg, J.
Publisher / Organisation
Greater Wellington Regional Council
The Wairarapa Fault east of Wellington, New Zealand ruptured on January 23, 1855, resulting in ground shaking, landslides, regional uplift, tsunamis, and >120 km of ground rupturing (Grapes, 1999; Downes and Grapes, 1999). Modern estimates of magnitude based on dislocation modeling of the observed distribution of vertical uplift, and on the felt extent of ground shaking (Fig. 1) suggest a moment magnitude (Mw) of 7.9 to 8.2 (Darby and Beanland, 1992; Dowrick, 1992), whereas revised measurements of surface offset and inferred rupture size suggest an Mw of ≥8.2 (Little and Rodgers, 2005; Rodgers and Little, in review). This makes the 1855 earthquake by far the largest seismic event in modern New Zealand history (Van Dissen and Berryman, 1996). The goal of this field trip is to provide participants with an overview of the tectonics, geomorphology, and earthquake geology of the active Wairarapa Fault, and for them to see the fault rupture and slip that took place during a recent (in this case, ~150 year old) earthquake. Recent work measuring offset landforms indicates that the amount of horizontal motion (strike-slip) that took place during the 1855 earthquake, while quite variable from place to place, has until recently probably been underestimated. One of the goals of this field-trip will be to visit sites in the southern Wairarapa Valley along the 1855 rupture where “smallest” strike-slip offsets of 15 -18.5 m, can be seen in the landscape and to discuss whether or not these displacements should be attributed to earthquake slip during 1855.