Constant layered
The Constant layered method builds a velocity cube composed of piecewise-constant layers. Each layer is bounded by a user-selected surface (horizon, time map, constant time, or topography) and carries its own interval velocity. Useful when the geology is naturally divided into zones with distinct, near-uniform velocities.
Required inputs
- Datum — elevation reference for the model.
- Layer table — one row per layer. Each row specifies the bottom of layer (a horizon, time map, constant time, or topography) and the velocity to apply inside that layer.
- Polygon (optional) — restricts the model to the area enclosed by the polygon.
Parameters
All parameters of this method are defined through the layer table. No additional smoothing or interpolation options are exposed — the velocity stays strictly constant within each layer.
Workflow
- Open Setting up the velocity model and select Constant layered.
- Set the Datum and, if needed, select a polygon to bound the model area.
- Populate the layer table. Use Add Row to add a layer, choose its bottom surface from the project, and enter the interval velocity.
- Repeat for every velocity zone from top to bottom of the section.
- Run the model. The wizard creates depth, interval velocity, average velocity, and time maps per layer.
Output
A layered velocity cube with interval velocity, average velocity, time and depth maps. Layer boundaries follow the selected surfaces exactly; velocity is discontinuous across boundaries and constant within each layer.
When to use
- Geologies with distinct velocity provinces separated by mapped horizons (for example salt/sediment, basalt/sediment).
- Quick time-to-depth conversion in layered basins when well control is sparse but structure is known.
- Initial model that will be refined later with checkshot- or marker-based methods.
Not suitable when velocity varies strongly inside a layer — use Checkshot extrapolation or a marker-based method instead.
See Also