Foam Faults: Demonstrating faulting and folding (Plate Tectonics)

Modeling an area some preexisting layers in here. We then put some extensional forces to pull across the part here, and one thing can do is to break, make false, and extend, as I pull my hands apart, the block in the middle falls down. These kinds of faults would be called normal faults where the block above the fault moves down. And imagine this happening now, not in just one nice smooth motion, as I'm doing it, but rather happening in a series of many, many jerks and the jerks are earthquakes. So this kind of deformation is happening across Nevada and the western part of Utah in the region of the western U.S. that we refer to as the basin and range. 

So if you ever drive across Nevada from west to east, you know that what happens is you'll drive through a valley for ten or 15 or 20 miles and then you'll climb up a pass over a range and then you'll drop down into another valley. So this kind of deformation extensional deformation has affected the basin and range in eastern California across Nevada and into Utah. And as it turns out, we have figured it out that the distance between San Francisco and Salt Lake City has approximately doubled over the course of the last 30 million years. Due to extension and due to faults that operate like that. Now take an area of the crust and try to compress it, push the ends together, and there's a couple of ways that it can respond. 

One way that it can respond is by making folds, we can demonstrate that by taking a deck of cards, trying to push the ends together, and as I push my two hands together, then we can make a fold. So we can take these preexisting horizontal layers, compress the crust and make folds. So if you look at various areas in the Rocky Mountains, which were exposed to compressional stresses, you'll find layers of rock, which are bent like this. We have two different names for these. If we bend the layer, we make a fold so that the limbs are going away from the high point here. We call that an ankle. So it's like an a for anion. If you fold it the other way, the central part goes down with respect to the sides. 

You're making like a U out of it. It's sort of a sink shape. Then that's called a sim card. That kind of a fold is called a sim card. So sim climbs, those kinds of folds can accommodate compressional stress. Another thing that the crust can do when it's under compression is it can also make faults which operate in the opposite sense to the kinds of faults that accommodate extension. So take the same foam blocks here, push the ends together, and the middle block then can pop up. In a series of earthquakes. So these kinds of faults are called reverse faults or thrust bolts, the block above the fault moves up with respect to the other blocks. So another kind of deformation here, shearing kinds of deformation, what will rocks do in that case? 

On a small scale here, rocks can shear and you can actually get alignments interesting alignments of the minerals in The Rock, these are very common in metamorphic rocks, so you can take something which maybe has a mineral in it that used to be a square or maybe used to be sort of circular in shape. And if you share that area, then you take that circle and turn it into an ellipse. So you make these flattened pancake Y sort of structures like you tend to see in the minerals of metamorphic rocks. That's because they've been sheared. 

On the big scale, if you think about a whole chunk of crust, being exposed to these kind of shearing forces, then you can also get false, which will accommodate cheering. And here's a foam foam model which can represent the San Andreas fault. So let's put it in map view here, north, up, and so to the right we have the North American plate over here. We have the Pacific plate over here. And if we put a shearing force on this, then we can make earthquakes in which the blocks of the crust move horizontally. With the Pacific plate moving towards northwest with comparison to the North American plane. So that's a model of foam fault model of the Sandra's fault.