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7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006
Marine
Surface Waves
1 SISMOCEAN, 23 rue de la cite blanche, 34200 Sete,
France, phone: ++33 467 536 192, [email protected]
2 SISMOCEAN, 34200 Sete, France
surveys are scheduled to acquire soil data for the design of pipeline landfalls, pipeline routes in
shallow water, jetties and breakwaters, loading / unloading facilities for LNG and oil terminals, and other coastal
developments. The underwater multichannel analysis surface wave [U-MASW] is a very efficient quantitative geophysical
tool to investigate the upper part of the seabed. It is also complementary to standard geophysical tools such as subbottom
profilers, seismic reflection which give qualitative information. U-MASW data are collected using a bottom-towed acoustic
source and a low frequency hydrophone streamer. The data processing is briefly addressed in this paper. The output is a
number of continuous shear wave [Vs] depth profiles covering the surveyed area. The Vs depth profile delivers quantitative
soil data directly linked to the shear modulus. This can be used to position boreholes in order to sample a maximum number
of soil configurations over the surveyed area. The U-MASW is also perfectly well adapted to investigate or localise areas
where very soft soils are encountered. Several sites have already been investigated by SISMOCEAN using the U -MASW
tool, and representative examples are presented in this paper. The U-MASW allows for a penetration depth ranging from
3m below seabed [bsb] to 50m bsb. The penetration depth is totally independent of the water depth. The sailing speed
during acquisition is 2 knots. Thus, 24 nautical miles can be surveyed per 12 hours shift. A route of 100 km long is surveyed
in less than 3 shifts, which makes the U-MASW a tool that should be considered for pipeline route surveys, as well as for
harbour development and pre-dredge surveys
.