Faults are an important part of geology and can be categorized in various ways. This blog post offers a brief introduction to the most common type of fault.
The 3 types of faults are:
- Normal faults
- Reverse faults
- Strike-slip faults
In this blog post, we will learn about these three types of faults and how they are formed.
An intuition for the 3 types of faults
Think of faults like taking a thick mat and snapping it:
- If it splits with an incline, it’s a dip-slip type of fault
- If it doesn’t have an incline, it’s strike-slip
Now, you have 2 mats. Put them on water so they float against each other. Here’s what could happen with their relative movements:
1. Normal Fault
The upper block moves downward relative to the lower block. (dip-slip)
2. Reverse/thrust Fault
The upper block moves upward relative to the lower block. (dip-slip)
3. Strike-slip fault
Both blocks slide horizontally across one another. (Strike-slip)
Now, you can substitute these terms:
- Fault = Fracture in two mats with relative movement
- Dip-slip = Incline split with vertical movement (upwards or downwards)
- Strike-slip = Straight split with horizontal movement (right or left lateral)
- Lithosphere = Floating mat
- Asthenosphere = Water
What is the speed of fault movement?
At faults, there is an enormous amount of friction between plates. Like a stretched spring, it stores tremendous potential energy near the fault.
- CREEP: If movement is slow at the fault, it’s called “creep”. By definition, “creep” means the fault is always absent of sudden movements that could create an earthquake.
- EARTHQUAKE: But if the two plates have a sudden jerky movement, this generates enough force to produce an “earthquake”. At this point, elastic waves shoot outwards which is the force one would feel from an earthquake.
Where do faults occur?
All plate tectonic boundaries are faults because they always have movement relative to each other. By definition, plate tectonics always converge, diverge, or slide across each other.
- NORMAL: Normal faults occur at divergent plate boundaries.
- REVERSE: Reverse faults are at convergent plates.
- STRIKE-SLIP: Strike-slip faults occur at transform plate boundaries.
But faults can occur within plates as fractures as well. For example, the New Madrid Fault is a massive fracture in Missouri. Over time, this fault has caused the Mississippi River to run a different course.
Reverse (thrust) faults are common in areas of compression. For example, reverse thrusts exist in areas with subducting plates such as along the coast of Japan.
How do faults work?
Now, you know the 3 types of faults are:
- Normal fault
- Reverse fault
- Strike-slip fault
Some consider a 4th type of fault:
- Oblique slip fault
Oblique slips are a combination of any of these 3 types of faults.
What else do you want to learn about faults? Please let us know with a comment below.
Types of Faults: Normal, Reverse and Strike-Slip
There are three types of faults that may occur in a rock. Normal faults occur when two plates, one on top of the other, slide past each other and create the fault. Reverse faults occur when one plate slides under the other, creating a vertical offset. Strike-slip faults happen when two plates move horizontally past each other.
If you are interested in this topic, then be sure to check out these online courses. There is a variety of universities that offer these programs from around the world so it’s easy to get started today.
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