What are the 4 basic classes of faults?
Earthquake Faults
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Dip-Slip Faults
Normal Fault
In a normal fault, the block above the fault moves down relative to the block below the fault. This fault motion is caused by tensional forces and results in extension. [Other names: normal-slip fault, tensional fault or gravity fault] EX., Sierra Nevada/Owens Valley; Basin & Range faults
Reverse Faults
In a reverse fault, the block above the fault moves up relative to the block below the fault. This fault motion is caused by compressional forces and results in shortening. A reverse fault is called a thrust fault if the dip of the fault plane is small. [Other names: thrust fault, reverse-slip fault or compressional fault] EX., Rocky Mountains, Himalayas
Strike-Slip Fault
In a strike-slip fault, the movement of blocks along a fault is horizontal. If the block on the far side of the fault moves to the left, as shown in this animation, the fault is called left-lateral. If the block on the far side moves to the right, the fault is called right-lateral. The fault motion of a strike-slip fault is caused by shearing forces. Examples: San Andreas Fault, California; Anatolian Fault, Turkey [Other names: transcurrent fault, lateral fault, tear fault or wrench fault.]
Transform Fault
A transform fault is a type of strike-slip fault wherein the relative horizontal slip is accommodating the movement between two ocean ridges or other tectonic boundaries. Additional animations on seafloor spreading and transform faults are available from Tanya Atwater.
Oblique Fault
Oblique-slip faulting suggests both dip-slip faulting and strike-slip faulting. It is caused by a combination of shearing and tension or compressional forces. Nearly all faults will have some component of both dip-slip (normal or reverse) and strike-slip, so defining a fault as oblique requires both dip and strike components to be measurable and significant.
Fault Models Lecture
Dr. Robert Butler, University of Portland, discusses Faults and Folds
Animations and videos are made in partnership with Earthscope, USGS, and Volcano Video & Graphics.
Please send feedback to Jenda Johnson.
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Asperities
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Multiple Asperities on a Strike-Slip Fault Plane
Oblique view of a right-lateral strike-slip fault with multiple asperities. When one asperity slips, there is an added load on the adjoining asperities. In a large earthquake there is a cascading effect as each zone that slips loads the next zone, which then slips, and so forth, sometime for hundreds of miles, in a process that can continue for 5 or more minutes. Narration by John C. Lahr taken from the "Spaghetti Vice" video lecture below.
Simple Models of Fault Movement with Single Asperity, High Friction, and Little or No Friction
Single Asperity Along Fault Zone
View looking into a fault zone with a single asperity. Regional right lateral strain puts stress on the fault zone. A single asperity resists movement of the green line which deforms before finally rupturing.
Low-friction Fault Zones
View looking into right- and left-lateral fault with low friction along fault contact. There is no deformation of the rock adjacent to contact.
John Lahr Demonstrates Asperities Along a Strike-Slip Fault
Animations and videos are made in partnership with Earthscope, USGS, and Volcano Video & Graphics.
Faults Explained
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