Brief note on seismic migration and inversion

Seismic inversion can be classified as

  • Methods based on iterative forward modeling
  • Methods based on downward wave field extrapolation

Inversion by iterative forward modeling:

  • Essentially in this method, elastic properties of the geological subsurface are estimated.
  • Given the seismic source and an initial subsurface model, a seismic data is simulated. The simulated data is then compared to the actual measured data and using the residual, the subsurface model is refined iteratively until the residual reaches a minimum.

Benefit: Really accurate
Drawback: Computationally very expensive

Inversion by downward wave field extrapolation:

  • It is the most commonly used method in the industry (migration). Here, the seismic waves (measured reflection data and the assumed/measured source) are downward extrapolated at every depth point. Thereafter, at every depth location a reflectivity is derived using an imaging condition.
  • In this method, reflectivity of the geological boundaries is estimated by extrapolating the source and reflected wave fields into the subsurface using pre-specified velocity model.
  • In the standard practice of migration, forward modelling of reflections is not done, neither is a residual calculated.

Benefit: Efficient compared to previous method
Drawback: The theoretical foundation is not reliable

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