93 research outputs found
Comparison of in situ and laboratory acoustic measurements on Lough Hyne marine sediments
No full textCompressional wave velocity and attenuation were measured at frequencies of 200–1500 Hz on seafloor sediments at Lough Hyne, Ireland, using a mini-boomer source and hydrophone array. Velocity and attenuation were also measured in the laboratory at 200–800 kHz on a 1 m long sediment core taken from the site. The in situ results indicate an average sediment phase velocity of about 1600 m/s and sediment quality factor of 10–20. The laboratory core measurements give an average phase velocity of 1793±26 m/s and quality factor of 16±5. The poorly sorted, Lough Hyne sediments are highly attenuating and highly dispersive when compared to values published in the literature for well-sorted, marine sediments such as clean sands and marine clays. The results are consistent with the few published data for poorly sorted sediments, and indicate that intrinsic attenuation is highest when the mass ratio of mud (clay + silt) to sand grade particles is close to unity. It is proposed that compliance heterogeneities are most abundant when mud and sand grade particles are present in roughly equal proportions, and that the observations support local viscous fluid flow as the most likely loss mechanism
The geology of the Madeira Abyssal Plain: further studies relevant to its suitability for radioactive waste disposal
No full textGreat Meteor East (distal Madeira Abyssal Plain): geological studies of its suitability for disposal of heat-emitting radioactive wastes
No full textKing's Trough Flank: geological and geophysical investigations of its suitability for high-level radioactive waste disposal
No full textPlate boundary reorganization at a large-offset, rapidly propagating rift
No full textTHE existence of rapidly spinning microplates along the southern East Pacific Rise has been documented by geophysical swath-mapping surveys1–6, and their evolution has been successfully described by an edge-driven kinematic model7. But the mechanism by which such microplates originate remains unknown. Proposed mechanisms1–10 have generally involved rift propagation11, possibly driven by hotspots or changes in direction of sea-floor spreading. Here we present geophysical data collected over the Earth's fastest spreading centre, the Pacific–Nazca ridge between the Easter and Juan Fernandez microplates (Fig. 1), which reveal a large-offset propagating rift presently reorganizing the plate boundary geometry. A recent episode of rapid 'duelling' propagation of the historically failing spreading centre in this system has created a 120 120 km overlap zone between dual active spreading centres, which may be the initial stage of formation of a new microplate
Towed Ocean Bottom Instrument TOBI: A New Deep-Towed Platform for Side-Scan Sonar and Other Geophysical Surveys
No full textTechnisch rapport Duinafslag
No full textDe TAW Leidraad Duinafslag van 1984 is vervangen door dit Technisch Rapport Duinafslag 2006 (TRDA2006). De hoofdreden daarvoor is dat er indertijd bij het opstellen van de Leidraad 1984 niet voldoende rekening is gehouden met het effect dat de golfperiode heeft op de mate van duinafslag. Metingen van golfkarakteristieken hebben inmiddels laten zien dat er tijdens zware stormvloedomstandigheden langere golfperioden kunnen voorkomen (Tp ? 16 - 20 s) dan waar indertijd rekening mee werd gehouden (Tp = 12 s). Met de procedures die in het TRDA2006 worden beschreven, wordt wel met het effect van deze langere golfperioden rekening gehouden. Daarnaast zijn er enkele andere nieuwe inzichten in het TRDA2006 verwerkt.TAW/EN
Discussion of: Project Jet Stream research flight no. 30, April 1957
No full textRead 17 January 1962. Presented by J.K. Bannon. See Q.J., 87, page 332.CER62ERR56
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