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The Depth group contains modules for converting seismic data from the time domain into the depth domain. Depth imaging is a critical step in the seismic processing workflow — it removes the distortions introduced by variable overburden velocities and produces a geologically accurate representation of subsurface structure.

Time-domain seismic sections display reflections as a function of two-way travel time. While this is a natural output of seismic acquisition, travel time is not the same as depth — the conversion depends on the velocity of the rock layers through which the seismic energy travels. Where velocities vary laterally or with depth, structures that appear flat or simple in time may have quite different shapes in depth. Depth conversion resolves these distortions by applying a velocity model to map each time sample to its true depth position.

Depth conversion in g-Platform uses an RMS (root-mean-square) velocity model to compute the depth at which each time sample belongs. The velocity model is sampled at the horizontal position of each trace, and the resulting depth-converted gather preserves the amplitude and character of the original seismic data while expressing it as a function of depth rather than time.

Modules in this group

Depth conversion — Converts a post-stack seismic gather from the time domain to the depth domain using an VRMS velocity model. The output is a depth-domain gather in which each sample represents a specific depth level (in metres), rather than a two-way travel time. The module also outputs the VRMS velocity profile used at each trace, which can be displayed alongside the time-domain data for quality control.

When to use depth conversion

Depth conversion is appropriate whenever the final deliverable must be expressed in depth units, for example when integrating seismic data with well logs, constructing depth-domain structural maps for reservoir modelling, or performing depth-domain amplitude analysis. It is especially important in areas with strong lateral velocity variations, such as below salt bodies, beneath thrust belts, or in areas of significant dip, where time-domain imaging can give a misleading picture of subsurface geometry.

The quality of depth conversion is directly dependent on the accuracy of the velocity model. A well-constrained VRMS velocity model — derived from velocity analysis, well control, or tomography — will produce a depth section that ties accurately to well markers and provides a reliable structural framework for interpretation.