Fault representation

In most illustrations and diagrams of the types of faults, there is always something similar. I noticed that there is a side of the hanging wall and foot wall which is slanted.

We're supposed to make a models for each type of fault; however, the material to be used will be difficult to cut diagonally. I'd like to know if it is necessary to have one side slanted? Or if having it vertical fine.

Please mention sources too. Thank you.

• What material? And is this a homework question? Aug 29, 2016 at 1:59
• It's not a homework question. We did not discuss much on faults and I wanted to know why one side of the hanging and foot wall is always slanted on representations and if it's necessary. Supposedly styrofoam.
– Ron
Aug 29, 2016 at 2:53

Faults are results of stress. The direction of the stress controls what kind of fault that is formed. The most fundamental reason for a fault to occur is horizontal compression or extension, even if it's often more complicated in reality.

Your two examples are dip-slip faults, with a vertical displacement as a result of horizontal stress.

In your first example, the normal fault. The total distance (from left to right) is increased. There has been an extension of the crust. If the fault plane would have been vertical, no distance would have been gained.

In the second example, the reverse fault, the distance is decreased. It's been a horizontal compression of the crust. The dip of a reverse fault is usually rather steep. If the dip is lower, you'll rather form a ramp. Typical for thrust faults.

Vertical fault planes are associated with strike-slip faults or ring faults above collapsing calderas or sinkholes. It's also common, but not for textbook examples of dip-slip faults.

So, unless you are showing a strike-slip fault, you have to find a way to cut diagonally. Do measure the horizontal displacement!

Addition about making fault models: We made a layer cake for a college some time ago and (of course) wanted to have a fault in it. The simplest way was to make a reverse fault, erode the uppermost layer of the hanging wall block and assume that the lowest exposed layer was of the same lithology (chocolate sandstone reservoir rock). However, it took some geoenginering to make it look good and we decided to make an impact crater next time.

• You can have a lot of fun by sawing up planks of wood to simulate faults, floating them in the bath to simulate back-tilting etc You usually don't have to look far to find examples of low angle, high angle, and vertical faults. Reverse faults are maybe less common outside of compressive tectonic areas. Bear in mind also that nature is nearly always more complex than your model, as with listric faults, and faults whose dip varies as you follow along strike. Any good circular saw should have an adjustment for the angle of cut - the angle of your red line from the vertical. Aug 28, 2016 at 2:46
• Yea, a listric fault would be difficult to model in pastry. Challenge accepted! Aug 28, 2016 at 4:17
• It seems like using styrofoam isn't the best choice. Instead, I'll just make a template on a folder and fold it to make it look like a fault. Thanks.
– Ron
Aug 28, 2016 at 7:51
• Use something like this? Aug 28, 2016 at 22:55