Civil Engineering Association

REFLECTION OF SEISMIC WAVES FROM ATTENUATING AND ANISOTROPIC OCEAN BOTTOM SEDIMENTS

There is an increasing trend towards recording marine seismic data directly on the seafloor.
This acquisition strategy is mainly motivated by the possibility to simultaneously measure
the three components of particle motion in addition to the pressure in the water column
immediately above the seabed. Such four-component (4C) seismic recordings thus allow
for the recording of S-waves in marine environments and offer the prospect of decomposing
the wavefield into its up- and down-going P- and S-wave constituents.
The assumptions for acquisition and processing of 4C data is today based on the ocean
bottom model as a welded acoustic-elastic contact at the seabed with a homogeneous
acoustic layer overlying a homogeneous elastic half-space. This may not hold in wide
areas of the oceans where the seafloor typically consists of soft, water-saturated sediments
characterized by having strong to very strong seismic attenuation. Moreover, cyclically
changing sedimentation processes lead to layering in the sediments, thus introducing
macroscopic seismic anisotropy, and overburden pressure and associated compaction effects
are likely to result in a strong velocity gradients.

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