Catastrophic Seismic-Related Events and Their Impact on Prehistoric Human Occupation, Coastal New Zealand
Goff, J. R., Mcfadgen, B. G., Antiquity
New Zealand, situated in the southern Pacific Ocean, straddles the boundary between two major tectonic plates. The Alpine Fault, a major morphological expression of this boundary, is over 500 km long and runs almost the entire length of the South Island. In recent times ruptures have occurred at intervals of about 260 years producing earthquakes with magnitudes of approximately 8.0 [M.sub.W] magnitude scale. Moment magnitude ([M.sub.W]) gives the most reliable estimate of earthquake size. 8.0 [M.sub.W] is a very big earthquake. (Bull 1996; FIGURE 1). In the Wellington region at least five active faults, the Wairarapa, Wellington, Ohariu, Shepherd's Gully, and Pukerua faults, are thought to be North Island continuations of the divided Alpine Fault (Van Dissen & Berryman 1996; FIGURE 1).
[Figure 1 ILLUSTRATION OMITTED]
Internationally, research into the impact of earthquake-related events on prehistoric coastal settlements is limited. Hutchinson & McMillan (1997) report a 3000-year history of temporary and permanent village abandonment along 600 km of coastline in British Columbia, Canada, based upon palaeoseismic and archaeological records, and native oral traditions. However, their hypothesis for village abandonment as a result of earthquake shaking and/or tsunami inundation was originally studied along the Oregon and Washington coasts in the United States (e.g. Woodward et al. 1990).
Although no explicit reference has been made to the impact of seismic activity on prehistoric Maori communities, except for passing reference to earthquakes (e.g. Best 1923), there are data that can be reinterpreted. In the early 1970s a team from Otago University carried out the first large-scale, regionally-focused archaeological field project in Palliser Bay, southern North Island (FIGURE 1). Environmental changes and changes in prehistoric occupation were explained in terms of human impact on the landscape and a climate change from a relatively calm, warmer period to a stormy cooler period (Leach & Leach 1979).
Here we examine evidence for the effects of catastrophic seismic-related events on prehistoric human occupation of the New Zealand coastline, using the Cook Strait region as a case-study (FIGURE 1).
Recorded impacts of earthquakes and tsunami in New Zealand since human settlement
Since the time humans first settled New Zealand, about 700 years ago, there have been at least eight fault ruptures in the Cook Strait region with a magnitude of 7.5 [M.sub.W] or greater (TABLE 1). Such large earthquakes are known to generate tsunami and to have considerable environmental impact (e.g. 1855 AD earthquake: Grapes & Downes 1997). Like most countries in and around the Pacific Ocean, New Zealand is directly exposed to both locally and distantly derived tsunami (Goff et al. 1998). However, locally derived tsunami, generated by either or both local fault ruptures and submarine land-sliding, tend to be more destructive (e.g. McSaveney et al. 2000).
TABLE 1. Summary of known major, local fault ruptures in the Cook Strait area and their estimated magnitudes since human occupation in New Zealand c. 700 years ago.
fault approx. est. reference rupture date magnitude (years AD) [M.sub.W] Awatere 1848 ~7.5 Grapes et al. 1998 Wairarapa 1855 8.0-8.3 Van Dissen & Berryman 1996 Ohariu 1290 7.6 [+ or -] 0.3 Van Dissen & Berryman 1996 Wellington 1250, 1450 ?, 7.6 [+ or -] 0.3 Van Dissen & Berryman 1996 Alpine 1220, 1450, ~8.0, ~8.0, ~8.0 Bull 1996; 1620, 1717 Yetton et al. …