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Modeling, migration, and demigration

University of Campinas, Brazil

Peter Hubral

Karlsruhe University, Karlsruhe, Germany

Corresponding author: lucio@ime.unicamp.br or js@ime.unicamp.br

Editor's note: A more extended and mathematically sophisticated treatment of this material can be found in "Seismic modeling by demigration" in the July–August issue of GEOPHYSICS.

The first 20% of the full text of this article appears below.

A new process in seismic reflection imaging called demigration has been designed as the inverse of migration and is, thus, easily confused with forward modeling. This paper will clarify the similarities and differences of modeling and demigration, and how both are related to migration.

An often-heard statement is that "seismic forward modeling is the inverse of seismic migration." We do not agree. In our opinion, seismic demigration deserves this title; forward modeling is, in turn, the "inverse of migration/inversion."

Before explaining seismic modeling by demigration, let us review what is commonly understood by seismic modeling, migration, migration/inversion, and demigration as true-amplitude imaging processes.

	Modeling

 
In Figure 1a, the dome-like reflector separates two homogeneous, acoustic media. Propagation velocities are 2500 m/s above the interface and 3000 m/s below it. Densities are equal, 1 g/cm³. Figure 1a also shows shot location S and corresponding receiver location G. They are separated by 500 m and have midpoint P. Simulation of seismograms for an earth model like Figure 1 is seismic modeling. In this case, simulation is restricted to computation of primary reflections—the key events in seismic modeling, imaging, inversion, and interpretation.

View larger version (42K): [in this window] [in a new window]   Figure 1. (a) Dome-like reflector denoting the discontinuity between two homogeneous acoustic half spaces. Also shown is the source-receiver pair S, G, and three corresponding isochrons. (b) Ray family for the primary reflections of a common-offset experiment with half-offset of 250 m over the dome-like reflector of Figure 1a.