Changes

While the earth's subsurface is more complicated than that shown in [[:file:seismic-migration_fig1.png|Figure 1]], the seismic data that would be obtained over the real earth can for all purposes be represented as a superposition of many diffraction curves generated by each of many boulder-like anomalies in the subsurface.

While the earth's subsurface is more complicated than that shown in [[:file:seismic-migration_fig1.png|Figure 1]], the seismic data that would be obtained over the real earth can for all purposes be represented as a superposition of many diffraction curves generated by each of many boulder-like anomalies in the subsurface.

[[:file:seismic-migration_fig2.png|Figure 2]] shows another depth section and associated seismic section for a subsurface consisting of a single dipping reflector. For a constant-velocity subsurface, the many weak diffractions from very closely spaced points along the reflector (of which five are shown in the figure) give rise, through constructive and destructive interference, to a net ''reflection'' along the straight-line envelope of the diffraction curves. Note that the reflection is displaced laterally from the true reflector position (the line connecting apexes of the diffraction curves). It is this lateral mispositioning of reflections from dipping reflectors that gave rise to the term ''migration'' for the process that corrects the positioning.

[[:file:seismic-migration_fig2.png|Figure 2]] shows another depth section and associated seismic section for a subsurface consisting of a single dipping reflector. For a constant-velocity subsurface, the many weak diffractions from very closely spaced points along the reflector (of which five are shown in the figure) give rise, through constructive and destructive interference, to a net ''reflection'' along the straight-line envelope of the diffraction curves. Note that the reflection is displaced laterally from the true reflector position (the line connecting apexes of the diffraction curves). It is this [[lateral]] mispositioning of reflections from dipping reflectors that gave rise to the term ''migration'' for the process that corrects the positioning.

[[:file:seismic-migration_fig3.png|Figure 3]] shows another perspective on this mispositioning. Reflections recorded at zero source-receiver offset follow ray paths that are perpendicular to the reflector. As a result, the reflection from the point on the reflector beneath point P, for example, would be recorded by the geophone at location G, to the right.

[[:file:seismic-migration_fig3.png|Figure 3]] shows another perspective on this mispositioning. Reflections recorded at zero source-receiver offset follow ray paths that are perpendicular to the reflector. As a result, the reflection from the point on the reflector beneath point P, for example, would be recorded by the geophone at location G, to the right.