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USGS CMG InfoBank: Stress and Strain

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Comment: 13:44 - 14:46 (01:02)
Source: Annenberg/CPB Resources - Earth Revealed - 8. Earth's Structures
Keywords: "tectonic activity", fold, structure, "Dee Trent", compression, tension, stress, strain, "elastic strain", "elastic limit", earthquake, deformation

Our transcription: Geologic structures like folds and folds are examples of strain, a change in the shape of the rock caused by stress.
"Stress" is the application of force on an area.
If you lean against a wall, you're putting some stress on it.
A strain is when the wall moves, so "strain" is the change in shape or volume.
"Plastic strain" is where stress has been applied to an object, and it's deformed, and then it stays in that same shape -- it doesn't resume its original shape.
"Elastic strain" is where the object is deformed, and then when the stress is removed it returns to its original shape.
Now, if you exceed its "elastic limit", then the object will break and shatter.
That's when we see folded rocks.
They have been subjected to a plastic strain.
Fracturing occurs when the strain exceeds the elastic limits of a material, and the rock breaks or fractures.

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