Seafloor Multiples Observed in OBS Data from the North Atlantic – Modelling of Sound Velocity in Water and Elastic Properties of Sediments


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Mechita.Schmidt-Aursch [ at ] awi.de

Abstract

Wide-angle seismic data acquired by use of air-guns and Ocean Bottom Seismometers (OBS) contain strong direct water arrivals and multiples, generally considered as noise and thus not included in the modelling. However, a recent study showed that standard ray-tracing modelling of the water multiples recorded off the Bear Island, North Atlantic, provided a reliable estimate of the velocity distribution in the water layer. Along the profile, the water velocity is found to change from about 1450 to approximately 1490 m/s. In the uppermost 400 m the velocities are in the range of 1455-1475 m/s, corresponding to the oceanic thermocline. In the deep ocean there is a velocity decrease with depth, and a minimum velocity of about 1450 m/s is reached at about 1.5 km depth. Below that, the velocity increases to about 1495 m/s at approximately 2.5 km depth. Here, we demonstrate that including the amplitudes in the modelling provide valuable information about the VP contrast at the seafloor, as well as the VP/VS ratio and attenuation (QP) of the uppermost sediments. The VP contrast at the seafloor is estimated at about 250 m/s, within a precision of approximately ±30 m/s. The VP/VS ratio in the uppermost sedimentary layer is modeled in the range 2.25-2.50, and the QP factor is estimated at 1000 for the water and 30-50 and 40-50 for the uppermost sediments. The values obtained for the sediments suggest a lithology dominated by silty clays, with porosity below average.



Item Type
Conference (Talk)
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Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
33rd General Assembly of the European Seismological Commission, 19 Aug 2012 - 24 Aug 2012, Moskow, Russia.
Eprint ID
32381
Cite as
Grad, M. , Schweitzer, J. , Mjelde, R. , Krüger, F. , Guterch, A. , Czuba, W. , Schmidt-Aursch, M. and Faleide, J. (2012): Seafloor Multiples Observed in OBS Data from the North Atlantic – Modelling of Sound Velocity in Water and Elastic Properties of Sediments , 33rd General Assembly of the European Seismological Commission, Moskow, Russia, 19 August 2012 - 24 August 2012 .


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