Page 24 - GeoPRISMS_Newsletter_Spring2018_Neat

Figure 2. Map showing location of existing Holocene records of coseismic vertical deformation along the Hikurangi margin (Hayward et al., 2016).
SHIRE Project paleoseismology study sites are located between 3-4, 4-5, and 7-8. Time line shows the estimated ages and accuracy limits for possible
earthquake events known from existing record. Correlation lines between study sites are also shown on the map to indicate potential lateral extent
of past earthquake ruptures..

Terrace cover beds have been sampled for optically stimulated buried beneath subtidal sediments. Because certain microfossils
luminescence (OSL) geochronology, and for the identification of have fidelity to the tidal frame, they can be used to assess how much
volcanic tephra and loess deposits of known ages. During the next two a coastline subsided during an earthquake. They can also be used to
years, terrace mapping and sampling will be expanded to new areas identify tsunami deposits because they indicate transport of marine
and drone imagery will be recorded for structure-from-motion studies. sediment into a coastal setting where such sediment does not occur
Project students will conduct digital terrain analyses using regional naturally. In this way, radiocarbon dating and microfossil analysis
topographic data to evaluate net deformation patterns, calculate on coastal sediments can be used to understand the timing and
morphometric indices, and outline morphotectonic domains. Overall, magnitude of past Hikurangi earthquakes and tsunamis. In 2017
the efforts of the coastal uplift team will provide new constraints on and 2018, Pilarczyk and students embarked on a sediment coring
the timing and spatial distribution of both short-term seismic cycle campaign that targeted low-energy depositional centers (i.e., marshes,
events, as well as longer-term cumulative deformation. lagoons) along the Hawke’s Bay coastline. Their mission was to find
Pilarczyk and students (Fig. 3 G-I) are using coastal sediments to evidence for past Hikurangi earthquakes that would supplement
develop long-term records of Hikurangi earthquakes and tsunamis. the short-term observational record by expanding the age range of
Microfossils such as foraminifera are used to recognize both subtle known events to include centennial and millennial timescales. The
and abrupt changes in sea level along a coastline. An abrupt change team’s ongoing investigations have led to the identification of newly
in sea level, caused by coseismic subsidence, indicates the occurrence discovered events that will help to better understand the seismic
of an earthquake and can be recognized along the coastline as a soil hazard for coastlines facing the Hikurangi margin. ■

References

Clark, K.J., B.W. Hayward, U.A. Cochran, L.M. Wallace, W.L. Power, A.T. org/10.1080/03014220709510536.
Sabaa, (2015), Evidence for past subduction earthquakes at a Litchfield, N.J., U.A. Cochran, K.R. Berryman, K.J. Clark, B.G. McFadgen, R.
plate boundary with widespread upper plate faulting: Southern Steele, (2016), Gisborne seismic and tsunami hazard: Constraints from
Hikurangi Margin, New Zealand. Bull. Seismol. Soc. Am., 105. doi: marine terraces at Puatai Beach GNS Science Report 2016-21, 99
10.1785/0120140291 Morton, J., (2018), Our sleeping Taniwha: Hikurangi’s tsunami threat.
Cochran, U., K. Berryman, J. Zachariasen, D. Mildenhall, B. Hayward, K. New Zealand Herald, 10 March 2018, https://www.nzherald.co.nz
Southall, C. Hollis, P. Barker, L.M. Wallace, B. Alloway, K. Wilson, Wallace, L.M., M. Reyners, U. Cochran, S. Bannister, P.M. Barnes, K.
(2006), Paleoecological insights into subduction zone earthquake Berryman, G. Downes, D. Eberhart-Phillips, A. Fagereng, S. Ellis,
occurrence, eastern North Island, New Zealand. Geol Soc Am Bull, A. Nicol, R. McCaffrey, R.J. Beavan, S. Henrys, R. Sutherland,
118, 1051-1074, doi:10.1130/B25761.1 D.H.N. Barker, N. Litchfield, J. Townend, R. Robinson, R. Bell,
Hayward, B.W., H.R. Grenfell, A.T. Sabaa, U.A. Cochran, K.J. Clark, L.M. K. Wilson, W. Power, (2009), Characterizing the seismogenic
Wallace, A.S. Palmer, A.S., (2016), Salt-marsh foraminiferal record of zone of a major plate boundary subduction thrust: Hikurangi
10 large Holocene (last 7500 yr) earthquakes on a subducting plate Margin, New Zealand. Geochem Geophys Geosyst, 10, Q10006.
margin, Hawkes Bay, New Zealand: Geological Society of America doi:10010.11029/12009GC002610
Bulletin, v.128, p. 896-915, doi:10.1130/B31295.1 Wallace, L.M., U.A. Cochran, W.L. Power, K.J. Clark, (2014), Earthquake
King, D.N.T., J. Goff, A. Skipper, (2007), Māori environmental and tsunami potential of the Hikurangi subduction thrust, New
knowledge and natural hazards in Aotearoa-New Zealand. Zealand insight from paleoseismology, GPS, and tsunami modelling.
Journal of the Royal Society of New Zealand, 37, 59-73, doi. Oceanography, 27, 104-117. doi:10.5670/oceanog.2014.46

24 • GeoPRISMS Newsletter Issue No. 40 Spring 2018