Summary
When velocity contrasts at the base of the near-surface zone are small, or when the base shows some degree of structural complexity, delay times of wavefronts transmitted through this zone may become raypath dependent. Due to the low velocity of S-waves this dependency can be translated into significant non-stationary delays. In order to remove this effect we transform the data into a domain in which amplitudes are a function of the raypath angle. Processing the statics in the t-p domain achieves this goal. The t-p transform automatically scans the data and captures the intrinsic ray parameter values that represent the data. This idea was implemented and tested on synthetic and field data using an interferometric approach. Results showed that after removing the statics in the t-p domain the stacking power and coherency of the events were significantly improved. Artifacts and resolution of the t-p transform still need to be addressed to improve this method.
Introduction
In processing multicomponent seismic data on land and on the ocean bottom, proper treatment of the effects of a complex near surface is a critical step. This is increasingly true as acquisition of broadband, wide-azimuth seismic data becomes the norm, and as the potential for full waveform inversion of land data becomes real, requiring both modelling of waves in the near surface and accurate accounting for surface wave modes. We seek an improvement in the converted wave statics solution not only to improve imaging, but also to extend the physical completeness of the earth model.
Within the context of seismic reflections, static time delays are the product of low-velocity sediments present near the surface. Changes in the velocity and thickness of these sediments introduce additional delays in the reflection traveltimes which disturb the actual shape and alignment of the subsurface reflections. This problem is magnified in the case of converted wave data due to the very low velocities of shear waves. Furthermore, the shear wave velocity contrast at the base of the near surface layer may not be sufficient to support the vertical ray-path assumption conventionally used for computation of static corrections. Cova et al. (2014) showed that even if the velocity contrast at the base of the near surface is large, the presence of dip on this interface may cause raypath-dependent delays that may differ significantly from the vertical traveltimes.
