Section 1: What is an Earthquake?

Activity #6: SCARP FORMATION

Materials:

• The scarp-formation animation (254K)
  

Procedure:

Imagine you are walking in the outdoors with an experienced geologist at your side. Suddenly, you come upon a roughly vertical cliff -- a scarp. Familiar with the area, the geologist assures you that this is a fault scarp. "But," she adds, "it was not created by any vertical motion along the fault." She then challenges you, in a friendly sort of way, to figure out how such a vertical feature could be created without vertical motion. After you've come up with a solution (or are forced to admit you're stumped) watch the animation, which shows how a scarp may be formed by non-vertical motion. Then consider the following:

1. What happened in the animation to produce the fresh scarp?
   Is this similar to your solution? Would the solution have been obvious, had you known what the hypothetical area looked like on a large scale?
   

2. There was already a sloping, grassy scarp in this area before the animated faulting produced a steep, fresh one. This grassy slope might have been an old fault scarp, but it could also have formed in other ways. What are some of the different ways such a feature could have formed?
   

3. This example points out a general rule of fault-related geology: the apparent offset of a feature (in this case, level ground offset vertically) is not always an indication of the actual displacement (horizontal cutting of a pre-existing scarp) along a fault. This is one of the more extreme examples of that rule.
   

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