Late Holocene uplift of beach ridges at Turakirae Head, south Wellington coast, New Zealand

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 M w 8.2 Wairarapa earthquake of AD 1855 January. The remaining chronology is established by radiocarbon dating, in situ 10 Be 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 G05031; Online publication date 26 July 2006 Received 8 July 2005; accepted 19 June 2006changed 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 14 C 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).

Conditional probability of rupture of the Wairarapa and Ōhariu faults, New Zealand

“…Timing of past surface ruptures Combining results from the historic record, trenching investigations at Riverslea, Cross Creek and Pigeon Bush ), uplifted beach ridges at Turakirae Head (McSaveney et al 2006), and lake disturbances at Lake Kō hangapiripiri (Cochran et al 2007) the timing of six ruptures of the Wairarapa Fault can be constrained (Fig. 2).…”

“…There are three sites along the southern Wairarapa Fault that constrain the timing of Event III: Cross Creek (2110Á 2340 cal yr BP; Little et al 2009), Turakirae Head (2060Á 2380 cal yr BP; BR3 of McSaveney et al 2006), Lake Kō hangapiripiri (2000Á2300 cal yr BP; transition DÁE of Cochran et al 2007). Taken collectively, and using AD 2010 as a datum, the best estimate for the timing of Event III is 2170Á2360 yr ago (Fig.…”

“…The timing of Event VI is constrained at Turakirae Head (6610Á6920 cal yr BP; BR5 of McSaveney et al 2006) and Lake Kō hangapiripiri (6300Á7250 cal yr BP; transition AÁB of Cochran et al 2007); the Cross Creek record of Little et al (2009) does not go back this far in time. Taken collectively, and using AD 2010 as a datum, the best estimate for the timing of Event VI is 6670Á6980 yr ago.…”

Lithology and hardness of shore platforms and surficial large boulders at Turakirae Head, New Zealand

“…Previous studies at Turakirae Head have examined ages and amounts of uplift of the beach ridges (e.g., Wellman 1967Wellman , 1969Moore 1987;Hull & McSaveney 1996;McSaveney et al 2006), analysis of shell midden information (Moore & McFadgen 1978), and pollen spectra from peat development on the raised marine terraces (Bagnall 1975;Mildenhall & Moore 1983). However, examination of beach sediments has occurred only west of the Orongorongo River mouth, to the west of the headland at Turakirae (Matthews 1980), and north of the study area around Ocean Beach in Palliser Bay (Matthews 1983) (Fig.…”

“…2), believed to have been formed by coseismic uplift (e.g., Wellman 1967Wellman , 1969Hull & McSaveney 1996;McSaveney et al 2006) since sea levels reached approximately their present levels in New Zealand c. 6500 yr ago (Gibb 1986). The last raised terrace is understood to have been elevated beyond the reach of all but overwash from storm waves on 23 January 1855, in association with movement on the Wairarapa Fault (Grapes & Downes 1996).…”