# Currents and voltages in an heterogeneous earthΒΆ

Usually the subsurface is not uniform (otherwise Geophysics and Earth Sciences would be meaningless). Some analytics solutions exist for very simple cases such as a sphere in a uniform field or a layered Earth. In all others cases, the use of numerical modeling techniques is required to compute the response of a particular physical property distribution. We use the differential equations described in Equations for modeling DC phenomenona to achieve it. You can also see the article Leading Edge for more information about numerical techniques.

The animation below, taken from the Mont Isa case history shows an example of such computation to visualize the current distribution for different sources in a highly structure underground: