A Three-Dimensional (3D) Earth Model, a geophysics and geology based three-dimensional model of the earth, is best described in terms of its exploration objective. Once a geologic target is chosen, the model can be designed to represent the geologic environment surrounding the prospective zone.

### Learning Objectives

After completing this module, you’ll be able to:

• Describe what a 3D Earth Model is.

• Describe how extensive the model should be.

• Determine what type of data and constraints are required for the model, and on which datum to compute the model effect.

• Explain how a 3D Earth Model can benefit your exploration objective through improved delineation of geologic structure and lithology.

A 3D Earth Model is a 3-Dimensional matrix of density or susceptibility based on geologic structure that can describe formation sequences, faults and intrusions. This combined geophysical and geological three-dimensional model of the earth, is best described in terms of its exploration objective. This means that once a geologic target is chosen, the model can be designed to represent the geologic environment surrounding the prospective zone.

Calculation of the gravity or magnetic effects requires the 3D Earth Model be defined in the space domain. Therefore, integration of time domain seismic data will require its conversion to the space domain. Each node value of density or susceptibility within the volume matrix is located with x,y,z (easting, northing, depth) coordinates. The geologic structure nodes within this volume will be defined by importing depth grids of geologic surfaces. Then the surfaces are assigned density or susceptibility as either constant values or laterally varying values defined by grids. In addition to grids, the structural matrix of density or susceptibility may be modified by including arbitrary 3D shapes defined either internally or imported.