In the left Project Explorer pane you may right click an existing fault and select Attributes:

The Fault Properties window will show up. In this window, under the Range section, tick "Finite" for the Range of the fault. 

You will then be able to define the Horizontal, Vertical and Influence Radii along with the Centre.

Here, we are actually defining the boundaries of a spheroid that is used to clip the fault plane and apply a smoothing factor to the fault's displacement function.