Gas Hydrate Studies in the Seismic Group at Dalhousie

Research of gas hydrates by the »Dalhousie Seismic Group has focused on wide angle seismic techniques.

• Gas hydrates are ice like solids that trap a gas molecule (usually methane) in a crystal lattice-cage of water molecules. This class of compound is called a clathrate, and includes other interesting compounds such as "buckyballs". This link contains more background information on »gas hydrates.

• Chris LeBlanc's undergrad thesis used forward modelling analysis of »Ocean Bottom Seismometer data to obtain a velocity profile for Scotian Slope sediments. This thesis is available from the Dalhousie Earth Sciences office.

• Following up on this initial work was a more extensive study in 2002 (hudson cruise 2002-046). These OBS data were of much higher quality, and inversion with Rayinvr was performed to obtain a more accurate and less subjective velocity model. This work also included analysis of bsr strength, sensitivity analysis, synthetic models, and migration / depth conversion of single channel seismic lines using the derived velocity model. The results of this study will hopefully be published in Marine and Petroleum Geology very soon.

• Wide angle data has also been collected for the »Haddock Channel and Flemish Pass area. Chris LeBlanc is currently analysing these data using high resolution modelling with Rayinvr. Initial plots of the OBS data indicate much improved quality, which should result in higher quality models. The layout of the survey will also allow for a true 2d velocity model with two instruments at both ends. This should improve the resolution and reliability of the result.

• CCGS Hudson cruise 2004-030 in the summer of 2004 allowed the use of 10 OBSs which were spaced close together. The seismic source for this survey was two GI guns, which produce a much cleaner signal than the sleeveguns that had been used before. The intention is to stack these OBS data to obtain a much higher signal to noise ratio, which should enable better quality picks. If the data is of sufficient quality, full waveform inversion is planned. There were two surveys of 10 OBSs, one in an area of strong BSRs and the other in an area with no BSRs. This study should provide an interesting look into the relationship between BSRs and velocity structure. This work is being performed by Jannet Cullen.