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Abstract
Holocene terraces at Turakirae Head on the south coast of the North Island, New Zealand, record four recent earthquakes from simultaneous rupture of the Wairarapa Fault and flexure of the Rimutaka Anticline. The lowest tread and riser is the modern marine platform and storm beach that began forming when the area was raised during the Mw 8.2 Wairarapa earthquake of AD 1855 January. The remaining chronology is established by radiocarbon dating, in situ 10Be surface‐exposure dating, and slip‐predictable uplift estimation. Prior to AD 1855, uplifts occurred at 110–430 BC (max. 9.1 m), 2164–3468 BC (6.8 m), and 4660–4970 BC (7.3 m). Earlier uplift of unknown magnitude occurred at c. 7000 BC but went unrecorded because of rapidly rising sea level. Sea level was still rising when the two oldest surviving beach ridges were raised.
Uplift at Turakirae Head in AD 1855 varied from 1.5 m at the Wainuiomata River to 6.4 m at the crest of the Rimutaka Anticline. Older beaches also are tilted, with the amount of tilt increasing with age. Coastal uplift at the anticline crest has averaged 3.32 ± 0.17 mm/yr over the past 9000 yr, and has changed little over the past 0.5 m.y. Uplift fits a slip‐predictable model of earthquake occurrence, and is log‐normally distributed with a mean of 7.3 ± 0.7 m. The most frequently occurring uplift is 7.1 ± 0.9 m. Uplift in AD 1855 was not significantly smaller than mean or mode, suggesting that the Turakirae Head sequence records four great earthquakes of at least similar magnitude to that of AD 1855. The mean earthquake recurrence interval is 2194 ± 117 yr; the modal interval is 2122 ± 193 yr.
At the crest of the anticline, the coastal platform was cut entirely during the postglacial rise of sea level until shortly before 4660–4970 BC. Away from the crest, however, it may have been partially cut during low sea level of the penultimate glaciation. The open‐ocean radiocarbon reservoir correction (δR) for 10 14C dates of coastal marine shells that died in AD 1855 at Turakirae Head is 3 ± 14cal. yrBP(andnot‐31 ± 13 cal. yr BP, the currently accepted δR for central New Zealand coastal waters).
