Faults | Earth Plate Tectonics and People: Foundations of Solid Earth Science
Earthquakes can also occur far from the edges of tectonic plates, along faults. Faults are In relation to the ground surface the slip involves sideway movement . Earthquakes and Faults Varying between 0 to mm per year, the movement of a plate is driven by convection in the Tectonic plates of the Earth. Arrows. The skin is divided into about a dozen tectonic plates. Plate boundaries are always faults, but not all faults are plate boundaries. The movement of the plates .
Earthquakes usually occur where two plates are running into each other or sliding past each other.
Fault Lines: Facts About Cracks in the Earth
Figure 1 - An image of the world's plates and their boundaries. Notice that many plate boundaries do not coincide with coastlines. Along Faults Earthquakes can also occur far from the edges of plates, along faults.
Faults are cracks in the earth where sections of a plate or two plates are moving in different directions. Faults are caused by all that bumping and sliding the plates do. They are more common near the edges of the plates. Types of Faults Normal faults are the cracks where one block of rock is sliding downward and away from another block of rock. These faults usually occur in areas where a plate is very slowly splitting apart or where two plates are pulling away from each other.
A normal fault is defined by the hanging wall moving down relative to the footwall, which is moving up.
Fault Lines: Facts About Cracks in the Earth
Figure 2 - A normal fault. The 'footwall' is on the 'upthrown' side of the fault, moving upwards. The 'hanging wall' is on the 'downthrown' side of the fault, moving downwards.
Reverse faults are cracks formed where one plate is pushing into another plate. They also occur where a plate is folding up because it's being compressed by another plate pushing against it.
At these faults, one block of rock is sliding underneath another block or one block is being pushed up over the other. A reverse fault is defined by the hanging wall moving up relative to the footwall, which is moving down.
Check out the sketches below to see a cartoon of what each of these fault types look like in cross-section. Eliza's nifty sketches Here we have a basic cross-section consisting of three rock layers: You can tell it's a cross-section because I drew a little tree Bob Ross-style! Now we'll apply some tensional stress to this terrain.
Tension has the effect of pulling and elongating. If this material were ductile, it would stretch and get thinner, but we are dealing with brittle rocks here, so instead they will break. The way this typically happens is by forming a fault at some angle to the bedding.
Then the whole package of rocks slides along this fault.
Tectonic Plates and Plate Boundaries
The type of fault formed here is called a normal fault. This terminology came from miners in Germany who noticed that most of the faults where they were working were of this nature, so they called them "normal," meaning typical.
As you can see, the fault has had the effect of dropping the block on the right with respect to the block on the left. If you saw something like this in the field, you'd be able to tell how much offset there was on the fault by measuring how much the layers had moved across the fault. If we instead apply compressive stress, this has the effect of squeezing and shortening the terrain. A fault will form that looks an awful lot like the normal fault in the previous example, but the motion on this fault is in the opposite direction.
This fault is called a reverse fault because it is the "reverse," meaning opposite, of normal. Reverse faults tend to form scarps--a scarp is the piece of rock that has been thrust up higher than the original surface level. The third typical fault type is the strike-slip fault. Strike-slip faults are distinct from the previous two because they don't involve vertical motion.
What is the connection between earthquakes and tectonic plates? – Earth Zone
They form via shear stress. These are not as easy to recognize in cross-section unless there has been so much movement on the fault that there are completely different rock types on either side of the fault. Most strike-slip faults are close to vertical with respect to the bedding. Faults at plate boundaries: Here are some animations of the lithosphere's sense of motion at plate boundaries. The first one is a mid-ocean ridge. Is the crust younger or older the farther it gets from the ridge?
The strike-slip fault depicted above is what geologists call a "left-lateral" strike slip fault. If you stand on one side of the fault and look across to the other side, the other side is moving to your left. If you have a nice grove of orange trees and the fault happens to cut right through your grove, the rows of orange trees will gradually become offset as the fault continues to move.