Footnote: Section 1
"Must strike-slip faults be vertical in dip (as shown)?"
You may note that the pictures and animations above show the strike-slip
faults as being essentially vertical in dip, whereas the dip-slip faults
had obvious hanging walls and footwalls. This is done for two reasons.
The first is that it is a fair generalization of reality.
Although strike-slip faults need not be vertical in dip, most
strike-slip faults have near-surface dips greater than 70 degrees.
Of course, some dip-slip faults also have near-vertical dips, so
those diagrams could also have used near-vertical faults, were it not
for the second reason -- maintaining the clarity of the relation
between hanging wall and footwall.
You may also notice that diagrams of dip-slip faults tend to have
a horizontal layer beneath the surface of the "block". This has
nothing to do with a realistic characterization of faults and everything
to do with the clarity of the diagram. There is no tendency for
dip-slip faults to form in places with horizontal sedimentary layers;
these layers merely make the dip slip in the diagram more obvious.
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