The resolution of commercial marine shear wave data is routinely decreased by the presence of statics. Little is understood about the origin of these statics.
Conventional techniques for obtaining static corrections in compressional wave data are not sufficient to compensate for the large magnitude of statics commonly observed in marine shear wave data. This study set out to test the hypothesis that statics in exploration-scale shear wave data are dominated by near-surface variations in sediment properties since the shear wave velocities of such sediments are both low and highly variable. Furthermore, it was suggested that only in situ seismic measurements can be used to accurately estimate static corrections.
Bottom-towed instrumentation was developed to facilitate the acquisition of seismic data in situ. The near-surface shear wave velocity field along a designated survey line in Red Wharf Bay, Anglesey, was estimated from Love wave, Scholte wave, Shear wave refraction and geotechnical data. Statics estimated from these velocity models were compared and then applied to mode converted shear wave data. Static estimated from in situ geotechnical measurements did not significantly improve the coherency
of the mode converted shear wave data since the empirical relationships used to
estimate shear wave velocity values, and thus statics, represent a gross simplification of the factors affecting the shear wave velocity. The estimation of shear wave statics using the inversion of Scholte wave data did not prove successful since the generation of Scholte waves at the seabed proved difficult due to poor source coupling and the limited availability of receivers. The estimation of the near-surface shear wave velocity field from the inversion of Love wave data demonstrated the ability to detect lateral variations in sediment properties. Statics estimated from the Love wave data improved the resolution of the mode conve1ted shear wave data. However, the inversion procedure averages the prope1ties over the length of the receiver array so
statics were often smoothed when compared to the predicted static shift. The
estimation of statics from the near-surface shear wave velocity model defined using refraction techniques provided the closest agreement to statics predicted from the converted wave and compressional wave data. The refraction method demonstrated the ability to detect both the short and long wavelength components of the statics resulting from near-surface variations in sediment properties. For the survey site, the contribution of near-surface sediments to the total shear wave statics was observed to be over 50%. The contribution of the near-surface sediments would have been greater in areas with less pronounced bedrock relief. It can be concluded that the estimation of shear wave statics using Love wave and shear wave refraction acquired in the manner described in this thesis can significantly improve the resolution of exploration-scale shear wave data.