Monochromatic infra-sound waves recorded offshore Ecuador: possible evidence of methane release |
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| Authors: | B Pontoise Y Hello |
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| Institution: | UMR Géosciences Azur-IRD-LGTE, case 119, University P. et M. Curie, 4 pl. Jussieu, 75252 –Paris;;UMR Géosciences Azur –BP48–06235 –Villefranche-sur-mer, France |
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| Abstract: | ABSTRACT Methane is known to be a greenhouse gas but it is difficult to estimate its significance. We have identified a new approach for monitoring fluxes of methane from large areas of sea floor. During spring 1998, we conducted an offshore passive seismic experiment using 13 three-component digital Ocean Bottom Seismometers. During this 3-week experiment, we recorded unusual sustained and intense monochromatic infrasound waves (6–7 Hz). The origin of the noise is tentatively interpreted as pressure-waves resulting from oscillating clouds of bubbles. Such clouds must have a characteristic size of ～ 10 m, at depths of 5–15 m, and must contain more than 1010 bubbles of 1 mm radius to produce the observed frequency. The presence of a Bottom Simulating Reflector in the study area suggests that gas seepage may occur at the seafloor, near 500 m depth. Then, bubbles of gas, namely methane, could form in the water column. Although highly speculative, Ocean Bottom Seismometer records could potentially be useful for monitoring gas seeps and/or related unusual behaviour of the seabed. |
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