This project involves the study of submarine methane  gas hydrates offshore Vancouver Island.   The research is carried out in collaboration with the Geophysics Group of Dr. G.D.  Spence, and with Dr. R.D. Hyndman at the Pacific Geoscience Centre.   The overall objective is to understand the physical nature of the gas hydrate system,  in particular the relationship of the hydrate with the geological structure, and  to estimate the hydrate concentration and the quantity of free gas. Seismic methods  provide an excellent means for investigating gas hydrates, since their presence is revealed  in seismic data by the so-called bottom simulating reflector (BSR) at on the  acquisition of new data.   In May 97, a collaborative experiment was carried out with the US Naval Rthe base of the  hydrate stability field. The goal of current research in the OA Chair Group is to invert  the seismic data to estimate the velocity profile at the BSR; from these data it is  possible to estimate the hydrate concentration and the quantity of free gas.

     At this stage, the effort has concentrated esearch  Laboratory, which contributed the deep towed high resolution seismic system (DTAGS)  in order to resolve the detailed velocity structure at the BSR, and with Dr. K.  Louden (Dalhousie University) who contributed his Ocean Bottom Seismometers to  obtain wide-angle reflection and refraction data below the BSR. Dr. Chapman was  the Chief Scientist on the research vessel John P. Tully for this sea trial. The  analysis of these data have revealed numerous vertical acoustic blank zones in the  seismic sections. These features are interpreted as locations of pathways for fluids  that transport subbottom methane to the sea floor. The data also provide the means  to determine the frequency response of the BSR over a wide frequency band from 30-650  Hz. The low reflectivity at the very high frequencies suggests that the BSR is a  relatively thin hydrate layer in which the velocity decreases by about 250 m/s  over a spatial scale of 6-8 m. The data are currently being processed by Mr. D.  Hannay as part of his Ph.D. thesis project.

     The new COAMS seismic array was used to acquire data  for a 3-D survey to study  the relationship of the pathways for methane-rich fluids and the geological  structure. The data were obtained in Aug 99 and are the basis for the PhD thesis  project of M. Riedel.

     Dr. Chapman co-supervised (with Dr. Spence) an M.Sc.  student, N. Ganguly  (Dec 98). His project used multichannel seismic data from the first joint  experiment in Sept 96 to map the BSR over an extensive area offshore, and to relate  the depth dependence of the BSR to heat flow at the sea floor (Ganguly et al, 2000).

Back to Top