50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...

measured by geological studies over many seismic
cycles (e.g., 10 kyr to millions of years). To address
this question we compare geological rates of
extension, shortening, fault slip and vertical axis
rotations, derived from cross sections, seismicreflection
lines, displaced landforms and
paleomagnetic data and measured over the last 5
Ma, with results from modelling of GPS velocities
from the Hikurangi Subduction margin in the North
Island. GPS velocities in the North Island are found
to be influenced by two fundamental processes (1)
elastic strain due to interseismic coupling on faults
in the region, and (2) long-term tectonic block
rotations (Wallace et al., 2004). It is the latter
component of the GPS velocity field that can be
directly compared to geological estimates of block
rotation and fault slip rates.
Regional analysis of the Hikurangi margin suggests
that within the uncertainties of the data the rates of
deformation for both data sets are, in most cases,
approximately equal and independent of the sample
period. Geological and geodetic datasets both
indicate rapid clockwise rotation (2-4 °/Ma) of the
eastern North Island. Extension and contractional
strains result from the rotation. Margin-parallel
velocity gradients arising from the rotation of the
eastern North Island account for up to 70% of the
margin-parallel component of Pacific/Australia
relative plate motion. Stable deformation rates over
time periods ranging from 5-10 years to millions of
years are consistent with the constant rates of plate
motion observed over similar temporal scales and
demonstrate the utility of GPS velocity fields for
constraining longer-term tectonic deformation (i.e.
> 1 earthquake cycle duration). The apparent
absence of faults at the ground surface
accommodating aseismic creep and of large
magnitude earthquakes over the last 10-15 years,
suggests that in the upper crust contemporary
geodetic strains are predominantly elastic. These
contemporary strains are spatially distributed across
much of the North Island, however, the
compatibility of block-rotation rates and fault-slip
rates from geological studies and those from
modelling of GPS data indicates that elastic strains
will, in the future, mainly be converted to narrow
zones of permanent deformation on, or close to, the
largest faults (i.e. those faults large enough to be
resolved in the regional geology data). Elastic strain
release is most likely to take place during large
magnitude earthquakes.
Wallace et al. 2004. JGR 109, B12406,
doi:10.1029/2004JB003241.
ORAL
FROM KAIKOURA TO KAITORETE: NON-
INVASIVE GEOPHYSICAL MAPPING OF
MAORI BURIAL SITES
David C. Nobes 1 , Leah Bateman,
Caroline Butland, Mark Flintoft,
Francie Gaiger, Joanna Lea, Scott Wilkinson
& Harry M. Jol 2
1 Department of Geological Sciences, University of
Canterbury, P.B. 4800, Christchurch
2 Department of Geography & Anthropology,
University of Wisconsin-Eau Claire, USA
(david.nobes*canterbury.ac.nz)
Sacred (tapu) sites need to be treated with care and
sensitivity. Non-invasive, non-destructive
geophysical surveying is an appropriate, optimal
way to map the nature and extent of such sites,
particularly burial sites – urupa. Since 1997,
geophysical methods have been successfully used
on urupa (Nobes, 1999). The response varies from
site to site, depending primarily on the nature of the
soil and the underlying bedrock.
The results from four sites representing three
physical settings are presented here:
1. The Oaro urupa is on top of a hill overlooking
the South Pacific, and was the first urupa to be
surveyed using geophysical methods (Nobes,
1999). The site’s clay soils overlie limestone
bedrock. Magnetic, electromagnetic (EM) and
ground penetrating radar (GPR) surveys were
completed. The responses are clear and
2.
unequivocal, once the influences due to fences
and the clay are removed.
The Koukourarata (Port Levy) and Wairewa
(Little River) sites are in loess overlying the
volcanic bedrock of Banks Peninsula. The EM
responses are apparent but are not as obvious
as for the magnetic surveys. The GPR surveys
have clear anomalous responses that in most
cases can be interpreted as graves (Bateman,
2003).
3. The Mangamaunu urupa is situated in coastal
beach sands, next to State Highway 1, just
north of Kaikoura and near the hamlet of
Hapuku. Anomalous geophysical responses are
all present but less obvious than for the Oaro,
Koukourarata and Wairewa sites. Nonetheless,
we can identify areas where the variable
geophysical response is indicative of
disturbance that is likely due to graves.
Bateman, L., 2003. Applications of near-surface
geophysics in the search for graves in Maori urupa.
B.Sc. (Honours) project in Engineering Geology,
Department of Geological Sciences, University of
Canterbury, 69 pp.
Nobes, David C., 1999. Geophysical surveys of burial
sites: a case study of the Oaro urupa, Geophysics,
64(2): 357-367.
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50 th Kaikoura05 -60- Kaikoura 2005