Changes

A number of forward modeling methods are available, and the choice of method generally depends on a tradeoff between the accuracy necessary and the desired computing time. In general, the type of data to be modeled, the complexity of the model, and the aspects of the data that need to be accurately modeled dictate the method that should be used.

A number of forward modeling methods are available, and the choice of method generally depends on a tradeoff between the accuracy necessary and the desired computing time. In general, the type of data to be modeled, the complexity of the model, and the aspects of the data that need to be accurately modeled dictate the method that should be used.

While field experiments always produce shot gathers, there are approximations available in numerical modeling that produce other data types directly. To simulate stacked data, for example, an exploding reflector model is often used. Virtual explosive sources are placed along all reflecting interfaces, with source strength proportional to the normal incidence reflection coefficient at that interface. This method produces accurate traveltimes and good zero offset amplitudes for geometric arrivals. Diffraction amplitudes are not accurate in this approximation, and multiples are not present. However, a complete stacked section can be generated in about the time it takes to generate a single shot gather. This efficiency makes the exploding reflector model the method of choice for most stacked section simulations. Another approximation, called ''image rays'', <ref name=Hubral_1977>Hubral, P., 1977, Migration: Some ray theoretical aspects: Geophysical Prospecting, v. 25, p. 739-745.</ref> makes it possible to simulate time-migrated data directly, again with approximations, but with significant time savings.

While field experiments always produce shot gathers, there are approximations available in numerical modeling that produce other data types directly. To simulate stacked data, for example, an exploding reflector model is often used. Virtual explosive sources are placed along all reflecting interfaces, with source strength proportional to the normal incidence reflection coefficient at that interface. This method produces accurate traveltimes and good zero [[offset]] amplitudes for geometric arrivals. Diffraction amplitudes are not accurate in this approximation, and multiples are not present. However, a complete stacked section can be generated in about the time it takes to generate a single shot gather. This efficiency makes the exploding reflector model the method of choice for most stacked section simulations. Another approximation, called ''image rays'', <ref name=Hubral_1977>Hubral, P., 1977, Migration: Some ray theoretical aspects: Geophysical Prospecting, v. 25, p. 739-745.</ref> makes it possible to simulate time-migrated data directly, again with approximations, but with significant time savings.

There are two classes of seismic modeling: ray tracing and wave equation methods. Implementation of both classes exists for one, two, and three dimensions; shot gather; common midpoint (CMP) gather; and stacked data simulation.

There are two classes of seismic modeling: ray tracing and wave equation methods. Implementation of both classes exists for one, two, and three dimensions; shot gather; common midpoint (CMP) gather; and stacked data simulation.