Diffraction modelling in N2D is restricted to 'diffractors' defined by physical  edges in the intersection points between two interfaces in the model. In this case, algorithms are implemented which simulate traveltimes and amplitudes for diffracted events. The amplitudes will e. g. be dependent of how the two interfaces are oriented relative to the incoming and outgoing rays at the diffractor. However, some users have asked for the possibilities of defining 'free' diffraction points anywhere inside the model and to calculate traveltimes corresponding to these 'artificial diffractors'. There is currently no direct option for defining such 'non-physical' diffraction points, but some possible 'work-arounds' can be proposed:‚Äč

  1. Halving the velocities in the model and put a shot point into the diffractor
    • - external action for varying velocity grids
    • - only zero offset modelling
    • - no direct comparison with other reflected events
    • + fast
    • + traveltimes can be viewed within N2D
  2. Put a shot point into the diffractor
    • - only zero offset modelling
    • - no direct comparison with other reflected events
    • - external action to double traveltimes
    • - traveltimes have to be exported to be viewed
    • + fast
    • + no changes to the model necessary
  3. NIP tracer + triangle
    • - creating a triangle in the model
    • - only zero offset modelling
    • + fast
    • + direct comparison with other reflected events possible
    • + traveltimes can be viewed within N2D
  4. CS/VSP tracer + triangle
    • - creating a triangle in the model
    • - slow
    • + finite offset modelling possible
    • + direct comparison with other reflected events possible
    • + traveltimes can be viewed within N2D