Because tectonic forces are powerful and constant, the rocks subjected to them will tend to break in a way that alleviates the stress they impart to the rocks. This is accomplished by fracturing and slipping in a manner that accomodates the push or pull of the greatest local stress.
For example, let's imagine you are in control of a large, square block of the Earth's crust. If you subject that block to stress by pushing on it from the west edge and the east edge, do you think that a north-south, vertical fracture will be likely to form? No, because such a break would not accomodate movement from the force you're applying to the block.
The activity below provides the opportunity to investigate how tectonic forces apply to faulting. You will have the chance to work through more examples like the one above, but with the help of fault-block figures.
How Tectonic Forces Affect Faults
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Determine a fault's slip by knowing the tectonic environment
around it -- and vice versa. |
The examples in this activity have hopefully shown you something about the "rules" that govern fault formation and motion. Still, you may wonder, wisely, how these simple rules apply to real-world situations, like that of the plate boundary in southern California. After all, the examples in the activity only used systems with one, two, or three faults -- not the several hundred major faults (not to mention the countless smaller ones) you find in southern California. Why are all those faults needed to accommodate the motion of the plates? After all, if the plate boundary here is a simple transform fault boundary, which plates sliding laterally past each other, wouldn't a single large fault would suffice in moving the two plates "smoothly" past each other? If so, then why are there so many faults here?
