Software Help with Software Modeling 3D~Def Guide User's Manual Definitions Introduction How to drive the deformation Input file and example 1 Output More examples Pitfalls and advice Get and run the code Selected references

Definitions | 3D~Def Guide


An element is a planar dislocation that may be used as a fault plane, a dike, a boundary of displacement, or almost anything that is planar.


An element may be (and usually is) divided into smaller elements, or subelements. The numbering or ordering system is as shown below, looking down the positive z-axis (planar coordinates) or from the hangingwall if that's clearer.

Ordering of subelements on a single element

1, 3

2, 3

3, 3

1, 2

2, 2

3, 2

1, 1

2, 1

3, 1

Bear in mind that this ordering is not the same as that which is output in vector format.

Inspection plane

The plane of coordinates to which output results are referred. For example, it is common to want displacements of the Earth's surface, so the inspection plane might be defined like this:

-10 10 0 90 0 20 20

where the first three numbers refer to the origin of the plane (in either global or in-plane coordinates, in this case, global), which is therefore at 10 km west and 10 km north of the coordinate origin and at the surface. The next two numbers are the strike (90) and dip (0) of the plane, and the last two refer to the along-strike and along-dip distances. Thus, this plane is flat and runs 20 km to the east and 20 km to the south of its origin. You can see that the specification of the inspection plane is the same as it is for any element.

Coordinate systems

We use three difference coordinate systems in 3d~def, each right-handed and shown in the table and figure below. The local system is used only inside the program, so the casual user can ignore it.

Coordinate systems used in 3d~def with reference to positive directions
System X Y Z
global east north up
planar (in-plane) along strike up-dip plane-normal into hangingwall
local along strike horizontal, normal to strike and into footwall up

Footwalls, hangingwalls, and relative displacements

The footwall lies under the hangingwall, so that a hangingwall moves up and over the footwall across a reverse fault, and it slides down and to a level below the footwall across a normal fault. If you use the right-handed convention (which we do in 3d~def) , then the hangingwall lies to the right of the strike direction.

Relative displacements across elements always refer to the motion of the hangingwall (HW) with respect to the footwall (FW). Thus, a negative shear displacement means that the HW has moved opposite to the strike direction (since the strike is the positive axis), which yields a right-lateral sense of motion. Likewise, a positive displacement in the dip direction indicates a reverse sense of motion. Here are some figures to make it all clear.


Are given in the table below:

feature units
element dimension km
element displacements cm
output displacements cm
stress same asYoung's modulus
strain none

Boundary conditions

These are the conditions applied to the central points of elements in the model input. They may be specified in terms of relative displacement, shear or normal stress, orientation of that stress, and absolute displacement. "code" numbers in the input file indicate which combination of conditions are being used. Because boundary conditions are applied to a plane, they are divided into components along the planar coordinates (strike, dip, and normal).

See driving the deformation for examples and details.


Last modified: 2019-12-24  02:29:41  America/Denver