New Zealand Journal of Geology and Geophysics abstracts

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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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