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

determine a record of secular variation and
paleointensity for New Zealand, and for an
environmental magnetic study of the Waipaoa
Catchment. Records of inclination of the
geomagnetic field, NRM intensity and magnetic
susceptibility are presented. Samples have low
NRM intensities (10 -6 –10 -5 A/m) and similar mean
destructive fields (MDF ~40mT), which indicate
that the magnetic minerals have a fine grain size,
are magnetically soft and easily demagnetised.
IRM measurements indicate magnetite is the major
magnetic mineral present in the cores. The
prognosis for paleomagnetic applications to
environmental and magnetic field studies is good as
is the potential for the development of a highresolution
paleomagnetic age model for the cores.
Samples are generally well behaved, with sufficient
magnetic intensity and variations in inclination and
magnetic susceptibility. NRM intensities appear to
provide reliable estimates of relative paleointensity
and variations in magnetic grain size,
concentrations of magnetic grains and magnetic
minerals are jointly indicated by �, MDF, ARM
and IRM.
POSTER
THE OFFSHORE MORPHO-STRUCTURE
OF THE SOUTHEASTERN VITI LEVU
SEISMIC SOURCE REGION, FIJI
Tariq Rahiman & Jarg Pettinga
Dept. of Geological Sciences, University of
Canterbury, P.B. 4800, Christchurch
(t.rahiman*geol.canterbury.ac.nz)
SE Viti Levu is a seismically active intra-plate
region of Fiji. The city of Suva (pop. ~150 000), in
the SE coast of Viti Levu is vulnerable to the
effects of potential offshore earthquakes and
associated seismic hazards. Recently acquired
SeaBat multibeam bathymetry and high resolution
seismic reflection data reveals for the first time the
physiography of the marginal slope of SE Viti Levu
in unprecedented detail. The marginal slope is
divided into five morphological domains, which are
primarily influenced by the underlying geology and
structure, and sedimentation from terrestrial
sources. The eastern slope, an area between 178.2
and 178.4 E longitude and 18.2 and 18.4 S latitude,
has had added influence from active tectonic
processes and seismicity. The surface of this slope
is scarred by linear submarine canyons, which are
the surface expressions of faulted grabens. These
submarine canyon faults extend onshore as fault
valleys and structural lineaments and they
collectively define continuous onshore/offshore
fault zones. These fault zones form a complex
network of faults, through which mesh style
coseismic faulting is responsible for the diffused
pattern of observed seismicity.
The submarine canyons are relict features from the
Late Miocene/Early Pliocene that have developed
primarily by downslope erosional processes. They
have experienced several episodes of re-incision
and infilling events, the latest occurring during the
late Pleistocene period of lowered sea level and
subsequent marine transgression. Presently,
headward erosion of the canyons into the marginal
shelf is occurring by seismically triggered
basinward sliding of masses at the canyon heads.
The head of these canyons indent the marginal shelf
and they coincide with deep water passages that
segment the barrier coral reefs protecting the inner
lagoon and coastline. The canyon heads are
positioned to act as sinks for the coastal sediment
transport system. Steep slopes of the canyon heads
are only marginally stable due to rapid deposition
of carbonate sediments from the barrier reef fronts
and outflowing lagoonal sediments through the reef
passages. Slope instability is exacerbated here by
slope oversteepening and undercutting by canyon
currents. Submarine landslides at the canyon heads
are initiated primarily by periodic short term
stresses generated by earthquakes, which have
induced destructive local tsunami in the past. The
canyon heads, all of which are within 5 km of the
coast, are potential local tsunami source areas that
pose a substantial threat to the coast.
POSTER
NUMERICAL MODELLING OF
SUBMARINE LANDSLIDE TSUNAMI AND
THE LOCAL TSUNAMI HAZARD OF SUVA
CITY, FIJI
Tariq Rahiman 1 , Jarg Pettinga 1 & Phil Watts 2
1 Dept. of Geological Sciences, University of
Canterbury, P.B. 4800, Christchurch
2 Applied Fluids Engineering, Inc., Long Beach,
California
(t.rahiman*geol.canterbury.ac.nz)
An important aspect of tsunami hazard assessment
and mitigation is to produce predictive simulations
of tsunami generation, propagation and run-up.
Such simulations require accurate geological data
on tsunami sources and a high quality
computational grid, which is preferably based on
high resolution bathymetry data. Predictive models
used for simulations need to be tested and proven
by running successful historical case studies. With
a complete range of critical input datasets required
for running predictive simulations, the coastal city
of Suva in Fiji, provides a rare opportunity for
assessing the tsunami hazard potential of submarine
landslides. Suva City has experienced damaging
historical earthquakes and associated submarine
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