Create a Density-Depth Table using an Expression

Use the DDT > Create DDT from Function option to build a vertical Density-Depth Table (DDT) using an expression relating density to depth. You may use any Oasis montaj expression operators. The new distribution will be created and displayed in the Properties panel.

Create Density-Depth Table from Function dialog options

New DDT name	Enter a descriptive name for the table.
Reference surface type	Specify whether the reference surface is defined by an elevation grid in the workspace, or an existing layer in the model.
	Reference surface grid Browse to find the reference elevation grid. Reference layer Select the reference surface from a list of layers in the model.
Offset range: 0 to	Set the maximum offset in the units specified. This must be a negative number.
Increment	Specify the interval at which the function will be sampled. This must be a negative number smaller than the maximum offset.
Function	Density = some function of the variable "offset".

Application Notes

GM-SYS 3D does not use the function directly. Instead, it uses the function to populate the entries in the Density/Depth Table. Each entry in the DDT actually used in the model causes an additional layer calculation. So a DDT with many entries will slow down the calculations.

The expression is a standard Oasis expression with the independent variable named "offset". If the expression generates a density greater than 5.0 g/cm³, the GX aborts with an error. If "End-Offset"/"Increment" is greater than 120 (the maximum size of the table), the GX aborts with an error.

Examples of other possible density functions:

2.153 - 2.0E-5*offset -1.0E-10*offset**2 + 2.0E-15*offset**3 Cubic polynomial

3.0 - 1.2*(10000)**2/(10000-offset)**2 Hyperbolic