HR: 08:00h
AN: S11D-01 INVITED    [Abstracts]
TI: Seabed property estimation from ambient noise recordings
AU: * Muyzert, E
EM: muyzert@slb.com
AF: Schlumberger Cambridge Research, High Cross Madingley Road, Cambridge, CB3 0EL, United Kingdom
AB: Processing and imaging of multi-component seismic data requires detailed knowledge of the shear velocity model of the subsurface. The near surface shear velocity is particular difficult to obtain using conventional seismic methods based on the analysis of shot generated data acquired in deep water. An analysis is presented of ambient noise recorded by an ocean bottom seismic cable developed for seismic exploration and monitoring. The data-set consists of 33 minutes of ambient noise recordings acquired in 270 m water depth. The ocean bottom seismic cable system has a hydrophone and three orthogonal geophones spaced at a 12.5 m interval over a total length of 5600 m. Analysis of the data revealed that below the frequency of 0.075 Hz the hydrophone data were found to be dominated by pressure variations due to sea surface waves. However, the corresponding seafloor compliance (the transfer function between pressure and velocity) was not observed on the vertical geophone component due to the limited 33 minutes recording length. Above 4 Hz the data were dominated by waterborne noise. The ambient noise wavefield at frequencies between 0.5 and 3 Hz was dominated by Scholte waves most likely generated by wave interaction. In addition Love waves were also observed but their excitation mechanism remains unexplained. Scholte and Love wave phase-velocities were picked in the frequency-wavenumber domain. In this domain the slowest velocity is apparent for inline propagation. Scholte wave phase-velocities were inverted for a near surface shear velocity model using a linearized inversion method. In an alternative approach, the spectral ratio of the vertical component and total ambient noise wavefield for the Scholte wave band was calculated and inverted for a near shear wave velocity model. This near surface model is in agreement with other published shallow shear velocity models and synthetics for this model fit well with the observed Scholte and Love wave phase velocity and the Scholte wave spectral ratio data.
DE: 3025 Marine seismics (0935, 7294)
DE: 3094 Instruments and techniques
DE: 7255 Surface waves and free oscillations
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: 2007 Fall Meeting