3D Velocity Model Building Based on Diffractions

Diffracted events are of great importance in the seismic processing because they allow to identify the presence of small heterogeneities, truncations, faults. However, to reliable interpret such subsurface features caused by diffractions, the letter ones should be properly imaged. An inherent part of the imaging is therefore a migration velocity analysis which should be tuned to diffractions. Moreover, imaging of diffractions is inherently a 3-D problem. In real geological environments one can not expect diffractors to be located below 2-D profiles. The 3-D effects of diffractors located transverse to the profile line leads to a smeared and less reliable diffraction images. We present a method for 3-D velocity analysis based on diffracted events. We perform migration velocity analysis by evaluating the semblance norm along diffraction traveltimes both in the depth and time domain. Finally, we perform Kirchhoff type of poststack migration with estimated velocities to validate the presented velocity analysis.