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21	Temporal Variations in the Compliance of Gas Hydrate Formations Roach, Lisa Aretha Nyala 20 March 2014 (has links) Seafloor compliance is a non-intrusive geophysical method sensitive to the shear modulus of the sediments below the seafloor. A compliance analysis requires the computation of the frequency dependent transfer function between the vertical stress, produced at the seafloor by the ultra low frequency passive source-infra-gravity waves, and the resulting displacement, related to velocity through the frequency. The displacement of the ocean floor is dependent on the elastic structure of the sediments and the compliance function is tuned to different depths, i.e., a change in the elastic parameters at a given depth is sensed by the compliance function at a particular frequency. In a gas hydrate system, the magnitude of the stiffness is a measure of the quantity of gas hydrates present. Gas hydrates contain immense stores of greenhouse gases making them relevant to climate change science, and represent an important potential alternative source of energy. Bullseye Vent is a gas hydrate system located in an area that has been intensively studied for over 2 decades and research results suggest that this system is evolving over time. A partnership with NEPTUNE Canada allowed for the investigation of this possible evolution. This thesis describes a compliance experiment configured for NEPTUNE Canada’s seafloor observatory and its failure. It also describes the use of 203 days of simultaneously logged pressure and velocity time-series data, measured by a Scripps differential pressure gauge, and a Güralp CMG-1T broadband seismometer on NEPTUNE Canada’s seismic station, respectively, to evaluate variations in sediment stiffness near Bullseye. The evaluation resulted in a (- 4.49 x10-3± 3.52 x 10-3) % change of the transfer function of 3rd October, 2010 and represents a 2.88% decrease in the stiffness of the sediments over the period. This thesis also outlines a new algorithm for calculating the static compliance of isotropic layered sediments. SEAFLOOR COMPLIANCE GAS HYDRATES BULLSEYE VENT TREND ANALYSIS SENSITIVITY ANALYSIS EIGENPARAMETER ANALYSIS HYDRATE MASS VARIATION LONG TERM TRENDS IN HYDRATE MASS MODIFIED YORK METHOD MARINE GEOPHYISCS MARINE SEDIMENT NEPTUNE CANADA SHEAR MODULUS GAS HYDRATE CONCENTRATIONS CASCADIA MARGIN MARINE GAS HYDRATES INFRA-GRAVITY WAVES SEISMOMETERS SCRIPPS DIFFERENTIAL PRESSURE GAUGE SCRIPPS DPG ODP SITE 889 BROADBAND SEISMOMETER gPhone DGP calibration Bottom Pressure Recorder Guralp CGM-1T Coherence transfer function bounds f-test bootstrapping wave propagation matrix static solution ocean bottom seismometer tsunami earthquakes Modified York least squares temporal variations linear trend in gas hydrates Power spectral densities 1D compliance solution 1D compliance algorithm seafloor compliance instrumentation Micro-g gravitimeter triple phase boundary equation ultra-low frequency seismics seafloor pressure spectrum seafloor gravity spectrum pacific ocean off-shore British Columbia seafloor observatory static compliance of layered structures geophysics gas hydrate characterization 0373

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Temporal Variations in the Compliance of Gas Hydrate Formations