Late Holocene surface ruptures on the southern Wairarapa fault, New Zealand: Link between earthquakes and the uplifting of beach ridges on a rocky coast T.A. Little1*, R. Van Dissen2†, E. Schermer3§, and R. Carne1# 1SCHOOL OF GEOGRAPHY, ENVIRONMENT AND EARTH SCIENCES, VICTORIA UNIVERSITY OF WELLINGTON, P.O. BOX 600, WELLINGTON 6140, NEW ZEALAND 2GNS SCIENCE, P.O. BOX 30368, LOWER HUTT 5010, NEW ZEALAND 3GEOLOGY DEPARTMENT, WESTERN WASHINGTON UNIVERSITY, MS9080, BELLINGHAM, WASHINGTON 98225, USA ABSTRACT The Holocene beach ridges at Turakirae Head, New Zealand, are remarkable because the fault that caused their uplift is accessible to paleo- seismic trenching. Based on 40 14C samples from eight trenches, we identify fi ve surface-rupturing earthquakes since ca. 5.2 ka (mean earth- quake recurrence of 1230 ± 190 yr). The paleoearthquake record includes two more events than were recorded by the uplift and stranding of beach ridges at Turakirae Head. We conclude that beach ridges may provide an incomplete record of paleoearthquakes on oblique-reverse faults. The southern end of the Wairarapa fault includes several splays in the near surface at variable distances from Turakirae Head. Variable partitioning of slip between these splays (and perhaps the subduction interface down-dip of them) is inferred to have caused variable mag- nitudes of coseismic uplift at the coast, where at least one <3 m throw is not recorded by preservation of a ridge. Variations in wave climate or sediment supply (or interseismic subsidence) may also infl uence the number of beach ridges preserved by governing the morphology of the storm berm and controlling its extent of landward retreat. Such retreat may cause a berm to overwhelm, or amalgamate with, the next-highest beach ridge, resulting in the omission of one ridge, as probably happened at Turakirae Head at least once. Our 14C data support the view that a widespread post–Last Glacial Maximum aggradational terrace in southern North Island, New Zealand, was abandoned soon after 12.1 cal yr B.P. From this, we infer that the Wairarapa fault has a late Quaternary slip rate of 11 ± 3 mm/yr. LITHOSPHERE; v. 1; no. 1; p. 4–28; Data Repository item 2009053. doi: 10.1130/L7.1 INTRODUCTION in uplift of the hanging wall of that dextral- a series of similarly expressed earthquakes that reverse fault near the southern coast of the North have ruptured the nearby Wairarapa fault during Slip on reverse (or oblique-reverse) faults dur- Island (Fig. 1A) and in the generation of a set the past ~7000 yr (e.g., Wellman, 1969; Moore, ing large earthquakes may be accompanied by a of tsunami waves up to ~9 m high (Grapes and 1987; Hull and McSaveney, 1996). signal of coseismic uplift (or subsidence) near Downes, 1997). The coseismic uplift reached a Globally, the uplifted Holocene beach ridges the coast that may be preserved in the geological maximum near Turakirae Head, where the pre- at Turakirae Head are remarkable because the record (Atwater, 1987; Berryman, 1993; Wilson 1855 storm beach ridge was raised by as much fault that caused their uplift does not lie sub- et al., 2007a). Repeated surface-rupturing earth- as 6.4 m (Begg and Mazengarb, 1996; Hull and merged offshore but is exposed on land nearby quakes have the potential to generate a suite of McSaveney, 1996; McSaveney et al., 2006). and is accessible to paleoseismic study (e.g., uplifted coastal beach ridges that faithfully record This fossil beach ridge is today preserved as the Ota and Yamaguchi, 2004). In this paper, the sequence of earthquakes on that fault. Such youngest of at least four tectonically uplifted we determine the ages of surface-rupturing a paleoseismically advantageous situation might beaches on the headland (Fig. 1B) (Aston, earthquakes on the southern Wairarapa fault be most likely where these earthquakes have all 1912; Wellman, 1969; McSaveney et al., 2006). using fault-trenching techniques and 14C dat- been similarly large, involving ruptures of similar In addition to its large magnitude, the histori- ing. Undertaken on the same part of the fault dimensions, slip, and—especially—uplift; where cally well-documented 1855 earthquake was known to have ruptured in 1855, and under- coastal conditions have been continuously favor- remarkable for infl uencing Charles Lyell (1868) pinned by more than 40 14C analyses collected able for the formation of beach ridges; and where to argue that earthquakes were associated with in eight trenches, our paleoseismic data allow the preservation potential of the abandoned land- vertical earth movements and slip on fault planes us to construct a comprehensive late Holocene forms has remained steadfastly high. (Grapes and Downes, 1997; Sibson, 2006), and earthquake chronology for the Wairarapa fault, New Zealand’s largest historic earthquake, the for its extremely large coseismic strike slip and to compare it with the published ages of Ms ~8.2 Wairarapa fault event in 1855, resulted (locally as high as ~18.5 m; Rodgers and Little, beach ridges at Turakirae Head. We are thus 2006). Since 1855, it has often been assumed that able to assess the completeness of that geo- the 1855 earthquake provided an analogue for morphic record and (potentially) the repeat- *Corresponding author e-mail: timothy.little@vuw. the style of deformation accompanying previous ability of large magnitude coseismic uplifts ac.nz. †[email protected]. earthquakes on this fault (e.g., Grapes, 1999). A on the fault. Although other studies have §[email protected]. corollary is that the uplifted gravel beach ridges compared beach ridge uplifts to the timing of #[email protected]. at Turakirae Head provide a complete record of historic earthquakes as much as ~500 yr ago 4 For permission to copy, contact [email protected] | © 2009 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/1/1/4/3044036/i1941-8264-1-1-4.pdf by guest on 28 September 2021 Late Holocene surface ruptures on the southern Wairarapa fault | RESEARCH NIDFB Hikurangi Trench Alfredton 50 Australian mm/yr Plate Mauriceville Northern 40° Tea Alfredton FaultSection 38 mm/yr Creek ui F. Alpine on ok Fault Hikurangi M Carterton Fault subduction zone Masterton F. 36 mm/yr Pacific Masterton Plate 41°S 170° 180° U Kaumingi Fault Waiohine River X D ult Wairarapa Fault Fa on Featherston gt n Pigeon Pacific Ocean li Wairarapa Valley el W Rimutaka Range Bush Figure 1. (A) Tectonic index map Ohariu Fault CentralCentral Coast Ranges U Rongotai Isthmus Cross showing major active faults and Fig. A other structures of the southern Wellington D Creek SectionSection Fault trenching North Island, New Zealand (largely Riverslea after Barnes, 2005; Begg and John- site (this study) ston, 2000; Lee and Begg, 2002), and Rimutaka location of sites along the Wairarapa Lake Kohangapiripiri Anticline SouthernSouthern SectionSection Fig. 2 Other localities fault where paleoseismic data have Orongaronga R. mentioned in text been collected previously and dur- Palliser Bay Turakirae ing this study (large open circles). Pliocene-Pleistocene strata Head Wharekauhau Smaller rectangles show location of Thrust 01020 detailed Wairarapa fault maps of Fig- ure A and Figure 2. Cross section X–X′ 176°E 175°E kilometers is presented in Figure 11B. Inset on Cape Palliser X’ A upper left shows plate-tectonic set- ting of New Zealand (plate motions taken from DeMets et al., 1990, 1994). NIDFB—North Island Dextral Fault Belt. (B) Oblique aerial photograph of uplifted beach ridges and Holocene wave-cut platform at Turakirae Head, view looking NW (photo by Lloyd Homer, GNS Science as annotated in McSaveney et al., 2006). The two uplifted Pleistocene marine terraces in the background were studied and assigned provisional ages by Ota et al. (1981). Distance between the two headlands is about 4 kilometers. B LITHOSPHERE | Volume 1 | Number 1 | www.gsapubs.org 5 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/1/1/4/3044036/i1941-8264-1-1-4.pdf by guest on 28 September 2021 LITTLE ET AL. (e.g., Bookhagen et al., 2006; Ferranti et al., but this component is typically a small fraction inferred strike-slip fault is an apparent south- 2007), these studies typically suffer from the of the strike slip (<20%; e.g., Berryman, 1990; ward continuation of the main, central section of short time span of the historic data and from Heron et al., 1998; Rodgers and Little, 2006). In the Wairarapa fault (Begg and Johnston, 2000). ambiguities regarding the location of the sur- the offshore to the east and west of Wellington, Evidence for an along-strike continuation of this face rupture accompanying those historically upper-plate deformation is inferred to be domi- western strike-slip strand has not been found at felt earthquakes. To our knowledge, ours is the nantly contractional (e.g., Barnes et al., 1998, the coast to the west of Turakirae Head (Begg fi rst study attempting a one-to-one comparison 2002; Lamarche, 2005). and Johnston, 2000). Instead, that fault appears between uplifted strandlines and paleoseismi- Elastic dislocation modeling of global posi- to step southward onto a thrust segment (Muka cally documented fault ruptures over a time tioning system (GPS) data and seismicity data Muka fault) entering Palliser Bay just east of span of ~5 k.y. Our results have general impli- near Wellington suggest that the Hikurangi Turakirae Head (Begg and Johnston, 2000; Lit- cations for the sensitivity of uplifted gravel subduction zone occurs 20–25 km beneath the tle et al., 2008). The Rimutaka anticline to the beach ridges as a paleoseismic “tape-recorder” surface trace of these faults, and that this gently west is an active SW-plunging fold expressed by on exposed, high-energy coasts, and the vari- (~8°) west-dipping part of the plate interface the steep topography of the coastal ranges and ability of rupture styles on individual oblique- is currently locked and accumulating elas- by differential uplift of the Holocene wave-cut slip faults.
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