Roberto,
Mirone does not know how to handle/create non-regular grids. The
SUBFAULT format gives as the description of a fault slip as a
collection of individual patches each one of them having a uniform
slip but where the slip varies from patch to patch. There is no
uniform or non-uniform grid assumption here. What Mirone does is to
compute the solution due to each individual, uniform slip described by
each patch and add them all. If you need to have the deformation on a
non-uniform grid you will have to take the Mirone's solution and
regrid it with some other tool that knows how to do that.
Hope it helps
Joaquim