Azimuthal Diffraction Imaging: a Land Data Example from Northern Switzerland

An important objective of the seismic exploration is assessment of the tectonic overprint. If available, 3D reflection seismic data is preferred as it provides the highest resolution of the subsurface images. Faults or fractures are typically indirectly analysed by interpreting discontinuities in vertical or horizontal reflection seismic images. Seismic diffractions represent a direct wavefield response from these tectonic features and thus allow for a more straight forward assessment of the tectonic overprint and mapping fracture density. We investigate a dedicated processing of seismic diffractions which comprises an azimuthal diffraction imaging.

The method is based on diffraction focusing. After reflections are removed from prestack data, diffracted waves are focused into their apexes yielding images of scatterers and edges. These images can be interpreted as an extent of inhomogeneities. We apply Kirchhoff time migration for a number of azimuths to focus diffractions. We also evaluate the coherence along the time-migration operators. Diffractions from the scattering points have a different phase response than diffractions from edges. This difference is acknowledged during the coherence evaluation. To further supress reflection left-overs, we apply a dynamic operator muting. This provides volumes of focused diffraction amplitudes, azimuthal orientation of faults, and coherence evaluated along the migration operators.