New Zealand Journal of Geology & Geophysics abstracts
Investigation of the role of gas hydrates in continental slope
stability west of Fiordland, New Zealand
Gareth J. Crutchley
Andrew R. Gorman
Miko Fohrmann
Department of Geology
University of Otago
PO Box 56
Dunedin 9054, New Zealand
Abstract Sediment weakening due to increased local pore fluid
pressure is interpreted to be the cause of a submarine landslide that
has been seismically imaged off the southwest coast of New Zealand.
Data show a distinct and continuous bottom-simulating reflection
(BSR)—a seismic phenomena indicative of the presence of marine gas
hydrate—below the continental shelf from water depths of c. 2400 m
to c. 750 m, where it intersects the seafloor. Excess pore fluid
pressure (EPP) generated in a free gas zone below the base of gas
hydrate stability is interpreted as being a major factor in the slope’s
destabilisation. Representative sediment strength characteristics have
been applied to limit-equilibrium methods of slope stability analysis
with respect to the Mohr-Coulomb failure criterion to develop an
understanding of the feature’s sensitivity to EPP. EPP has been
modelled with representative material properties (internal angle of
friction, bulk soil unit weight and cohesion) to show the considerable
effect it has on stability. The best estimate of average EPP being
solely responsible for failure is 1700 kPa, assuming a perfectly
elastic body above a pre-defined failure surface in a static
environment.
Keywords gas hydrate; excess pore fluid pressure;
submarine slope stability; marine seismic reflection
G07008; Online publication date 10 October 2007; Received 4 May
2007; accepted 18 September 2007
New Zealand Journal of Geology & Geophysics, 2007, Vol. 50:
357–364
0028–8306/07/5004–0357 © The Royal Society of New Zealand 2007
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