New Zealand Journal of Geology and Geophysics abstracts
Seismic images of gas conduits beneath vents and gas hydrates on Ritchie
Ridge, Hikurangi margin, New Zealand
Ingo A. Pecher*
Stuart A. Henrys
Hia Zhu
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
*email: i.pecher@gns.cri.nz
Abstract Recently acquired seismic reflection data across
the southern edge of Ritchie Ridge, a prominent bathymetric high on the Hikurangi
margin, display zones of high amplitudes and reflections that crosscut strata.
We interpret the latter as bottom-simulating reflections which are commonly
associated with gas beneath gas hydrates. An analysis of reflection strength
indicates the high-amplitude zones are caused by free gas in the pore space
of sediments, probably migrating upward along layers. One of the high-amplitude
regions is situated beneath the projected location of a known gas vent site.
The seismic data appear to image the conduits that supply this vent site with
gas. The seafloor in most of the study area is likely to be within the zone
of gas hydrate stability, depending on bottom water temperatures and hydrate
composition. Hence, gas appears to be venting through the gas hydrate stability
zone, favouring locally high concentrations of gas hydrates.
Keywords gas hydrates; New Zealand; vents
G03008; Received 8 April 2003; accepted 24 December 2003; Online publication
date 20 May 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 275–279
0028–8306/04/4702–0275 © The Royal Society of New Zealand 2004
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