Resource Evaluation of Marine Gas Hydrate Deposits Using Seafloor Compliance Methods

• Published in: Annals of the New York Academy of Sciences
• Main Authors: WILLOUGHBY, ELEANOR C., LATYCHEV, KONSTANTIN, EDWARDS, R. NIGEL, MIHAJLOVIC, GEORGE
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2000
• Subjects: History and Philosophy of Science; General Biochemistry, Genetics and Molecular Biology; General Neuroscience; Methane hydrate
• Online Access: http://dx.doi.org/10.1111/j.1749-6632.2000.tb06768.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1749-6632.2000.tb06768.x; https://nyaspubs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1749-6632.2000.tb06768.x

A bstract : We introduce the theory and practice of the compliance method: a new tool for assessing offshore methane hydrate deposits. Compliance is defined as the transfer function between the vertical displacement of the seafloor and the corresponding pressure expressed as a function of frequency. It is sensitive to the elastic parameters of the underlying sediments, particularly the shear modulus. We have measured normalized compliance from 0.001 to 0.049 Hz, using ocean surface gravity waves as a source, at sites in Cascadia near the Ocean Drilling Program (ODP) hole 889B. A differential pressure gauge, datalogger, and self‐leveling gravimeter were lowered to the seafloor, and each site was occupied for eight hours. The compliance estimates are reproducible and are consistent with other available data and simple models of sediment physical properties. Shear strength is increased from a normal profile in the uppermost few hundred meters, possibly an effect of grain cementation within a known hydrate layer. The magnitude of the increase may be associated with the total mass of hydrate present irrespective of the details of its distribution.