50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
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measured by geological studies over many seismic<br />
cycles (e.g., 10 kyr to millions of years). To address<br />
this question we compare geological rates of<br />
extension, shortening, fault slip and vertical axis<br />
rotations, derived from cross sections, seismicreflection<br />
lines, displaced landforms and<br />
paleomagnetic data and measured over the last 5<br />
Ma, with results from modelling of GPS velocities<br />
from the Hikurangi Subduction margin in the North<br />
Island. GPS velocities in the North Island are found<br />
to be influenced by two fundamental processes (1)<br />
elastic strain due to interseismic coupling on faults<br />
in the region, and (2) long-term tectonic block<br />
rotations (Wallace et al., 2004). It is the latter<br />
component of the GPS velocity field that can be<br />
directly compared to geological estimates of block<br />
rotation and fault slip rates.<br />
Regional analysis of the Hikurangi margin suggests<br />
that within the uncertainties of the data the rates of<br />
deformation for both data sets are, in most cases,<br />
approximately equal and independent of the sample<br />
period. Geological and geodetic datasets both<br />
indicate rapid clockwise rotation (2-4 °/Ma) of the<br />
eastern North Island. Extension and contractional<br />
strains result from the rotation. Margin-parallel<br />
velocity gradients arising from the rotation of the<br />
eastern North Island account for up to 70% of the<br />
margin-parallel component of Pacific/Australia<br />
relative plate motion. Stable deformation rates over<br />
time periods ranging from 5-10 years to millions of<br />
years are consistent with the constant rates of plate<br />
motion observed over similar temporal scales and<br />
demonstrate the utility of GPS velocity fields for<br />
constraining longer-term tectonic deformation (i.e.<br />
> 1 earthquake cycle duration). The apparent<br />
absence of faults at the ground surface<br />
accommodating aseismic creep and of large<br />
magnitude earthquakes over the last 10-15 years,<br />
suggests that in the upper crust contemporary<br />
geodetic strains are predominantly elastic. These<br />
contemporary strains are spatially distributed across<br />
much of the North Island, however, the<br />
compatibility of block-rotation rates and fault-slip<br />
rates from geological studies and those from<br />
modelling of GPS data indicates that elastic strains<br />
will, in the future, mainly be converted to narrow<br />
zones of permanent deformation on, or close to, the<br />
largest faults (i.e. those faults large enough to be<br />
resolved in the regional geology data). Elastic strain<br />
release is most likely to take place during large<br />
magnitude earthquakes.<br />
Wallace et al. 2004. JGR 109, B12406,<br />
doi:10.1029/2004JB003241.<br />
ORAL<br />
FROM KAIKOURA TO KAITORETE: NON-<br />
INVASIVE GEOPHYSICAL MAPPING <strong>OF</strong><br />
MAORI BURIAL SITES<br />
David C. Nobes 1 , Leah Bateman,<br />
Caroline Butland, Mark Flintoft,<br />
Francie Gaiger, Joanna Lea, Scott Wilkinson<br />
& Harry M. Jol 2<br />
1 Department of Geological Sciences, University of<br />
Canterbury, P.B. 4800, Christchurch<br />
2 Department of Geography & Anthropology,<br />
University of Wisconsin-Eau Claire, USA<br />
(david.nobes*canterbury.ac.nz)<br />
Sacred (tapu) sites need to be treated with care and<br />
sensitivity. Non-invasive, non-destructive<br />
geophysical surveying is an appropriate, optimal<br />
way to map the nature and extent of such sites,<br />
particularly burial sites – urupa. Since 1997,<br />
geophysical methods have been successfully used<br />
on urupa (Nobes, 1999). The response varies from<br />
site to site, depending primarily on the nature of the<br />
soil and the underlying bedrock.<br />
The results from four sites representing three<br />
physical settings are presented here:<br />
1. The Oaro urupa is on top of a hill overlooking<br />
the South Pacific, and was the first urupa to be<br />
surveyed using geophysical methods (Nobes,<br />
1999). The site’s clay soils overlie limestone<br />
bedrock. Magnetic, electromagnetic (EM) and<br />
ground penetrating radar (GPR) surveys were<br />
completed. The responses are clear and<br />
2.<br />
unequivocal, once the influences due to fences<br />
and the clay are removed.<br />
The Koukourarata (Port Levy) and Wairewa<br />
(Little River) sites are in loess overlying the<br />
volcanic bedrock of Banks Peninsula. The EM<br />
responses are apparent but are not as obvious<br />
as for the magnetic surveys. The GPR surveys<br />
have clear anomalous responses that in most<br />
cases can be interpreted as graves (Bateman,<br />
2003).<br />
3. The Mangamaunu urupa is situated in coastal<br />
beach sands, next to State Highway 1, just<br />
north of <strong>Kaikoura</strong> and near the hamlet of<br />
Hapuku. Anomalous geophysical responses are<br />
all present but less obvious than for the Oaro,<br />
Koukourarata and Wairewa sites. Nonetheless,<br />
we can identify areas where the variable<br />
geophysical response is indicative of<br />
disturbance that is likely due to graves.<br />
Bateman, L., 2003. Applications of near-surface<br />
geophysics in the search for graves in Maori urupa.<br />
B.Sc. (Honours) project in Engineering Geology,<br />
Department of Geological Sciences, University of<br />
Canterbury, 69 pp.<br />
Nobes, David C., 1999. Geophysical surveys of burial<br />
sites: a case study of the Oaro urupa, Geophysics,<br />
64(2): 357-367.<br />
POSTER<br />
50 th <strong>Kaikoura</strong>05 -60- <strong>Kaikoura</strong> <strong>2005</strong>