Changes

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.

Ray theory uses the fact that energy in the form of ''rays'' travels along minimum time paths in the model. As in optics, rays bend when velocities change, obeying Snell's law, and are partially reflected when velocity or density discontinuities are encountered. Traveltimes of reflected arrivals correspond to the times of the minimum time paths, while amplitudes are a combination of geometric spreading and reflection coefficient. The reflection coefficient, based on the Zoeppritz equations for elastic media, depends on the velocities and densities on both sides of the interface, as well as on the incidence angle of the ray.

Ray theory uses the fact that energy in the form of ''rays'' travels along minimum time paths in the model. As in optics, rays bend when velocities change, obeying [http://en.wikipedia.org/wiki/Snell%27s_law%20Snell's%20law Snell's law], and are partially reflected when velocity or density discontinuities are encountered. Traveltimes of reflected arrivals correspond to the times of the minimum time paths, while amplitudes are a combination of geometric spreading and reflection coefficient. The reflection coefficient, based on the Zoeppritz equations for elastic media, depends on the velocities and densities on both sides of the interface, as well as on the incidence angle of the ray.

Ray methods usually give very accurate traveltimes and accurate amplitudes for geometric arrivals if the model is sufficiently smooth. These methods are efficient, and computing time is low to moderate. Diffractions and multiple reflections can be added, though at high computing times and never with complete accuracy. Ray methods are the methods of choice for many structural verification problems and are quite useful for stratigraphic problems if the interfaces are reasonably smoothly varying.

Ray methods usually give very accurate traveltimes and accurate amplitudes for geometric arrivals if the model is sufficiently smooth. These methods are efficient, and computing time is low to moderate. Diffractions and multiple reflections can be added, though at high computing times and never with complete accuracy. Ray methods are the methods of choice for many structural verification problems and are quite useful for stratigraphic problems if the interfaces are reasonably smoothly varying.