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3-D TRAVEL TIME TOMOGRAPHY INVERSION FOR GAS HYDRATE DISTRIBUTION FROM OCEAN BOTTOM SEISMOMETER DATA

University of British Columbia. Department of Chemical and Biological Engineering; International Conference on Gas Hydrates (6th : 2008 : Vancouver, B.C.)

This paper presents results of a seismic tomography experiment carried out at the Bullseye cold vent site offshore Vancouver Island. In the experiment, a seismic air gun survey was recorded on an array of five ocean bottom seismometers (OBS) deployed around the vent. The locations of the shots and the OBSs were determined to high accuracy by an inversion based on the shot travel times. A three-dimensional tomographic inversion was then carried out to determine the velocity structure around the vent, using the localized source and receiver positions. The inversion indicates a relatively uniform velocity field around and inside the vent. The velocities are close to the values expected for sediments containing no hydrate, which supports previous claims that the bulk concentrations of gas hydrates are low at the site. However, the largest resolved velocity anomalies of + 25 m/s are spatially within the limits of the acoustic blank zone seen in multichannel seismic data near the Bullseye vent. The velocity inversion is consistent with zones of high concentration (15-20 % of the pore space) in the top 50-100 m of sediment.

Gas hydrates; Ocean bottom seismometers; Cold vent; Seismic tomography

Text

eng

Vancouver : University of British Columbia Library

10.14288/1.0041076

Non UBC

Unreviewed

http://creativecommons.org/licenses/by-nc-nd/4.0/