How do faults work

To view this site, enable JavaScript by changing your browser options and try again. Jump to main content. Sometimes faults move when energy is released from a sudden slip of the rocks on either side.

Most earthquakes occur along plate boundaries, but they can also happen in the middle of plates along intraplate fault zones. During the winter of —, a series of earthquakes struck New Madrid, Missouri. More recently, the Sichuan region in China suffered a devastating intraplate earthquake in Some faults are visible at the surface, but others lie deep within the crust. Just as there are various types of plate movements, there are also different types of faults.

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You'll be happy you did. Each type is the outcome of different forces pushing or pulling on the crust, causing rocks to slide up, down or past each other. Strike-slip faults indicate rocks are sliding past each other horizontally, with little to no vertical movement. Both the San Andreas and Anatolian Faults are strike-slip.

Normal faults create space. Two blocks of crust pull apart, stretching the crust into a valley. Reverse faults , also called thrust faults, slide one block of crust on top of another. These faults are commonly found in collisions zones, where tectonic plates push up mountain ranges such as the Himalayas and the Rocky Mountains.

Strike-slip faults are usually vertical, while normal and reverse faults are often at an angle to the surface of the Earth. The different styles of faulting can also combine in a single event, with one fault moving in both a vertical and strike-slip motion during an earthquake. All faults are related to the movement of Earth's tectonic plates. The biggest faults mark the boundary between two plates. 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. 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. See in the animation below how the various fault types move. Animation is silent and comes from IRIS. Each of these three types of faults is marked in a standard way on a geologic map.

I've sketched those symbols below. Can you identify the type of faulting occurring at each plate boundary in the map below? Check your answer here. Have another look at Figure 1 from de Boer et al. What type of faulting is being depicted on that map? Can you picture in three dimensions how the lithosphere is moving in that map?

Think about it and compare your idea to my sketch and a captioned version.