Focussing CSP gather semblance images for foothills time migration
John C. Bancroft, Yong Xu, M. Gratziella Kirtland Grech
Equivalent offset migration (EOM) was applied to a 2-D numerical model of the Canadian Rocky Mountain foothills. Data beneath a low velocity wedge was particularly difficult to image. Analysis of the common scatter point (CSP) gathers and their semblance plots showed a number of potential velocity picks that came from the same reflector. These multiple semblance points were attributed to lateral velocity variations that tilt the diffraction energy in two-sided CSP gathers.
The energy in a CSP gather was tilted by varying amounts and the semblance computed then combined into a movie. The effects of tilting the CSP gathers can be evaluated by running the movie and comparing the location and size of the semblance clouds with the estimated velocity profile. Unfortunately, the area with the greatest tilt was not available for tilt analysis, but an equally interesting area is evaluated.