High School Earth Science: Earthquakes - Stress in Earth’s Crust — Flashcards

Stress and How It Changes Rock    
Stress is force applied to an object. In geology, stress is the force per unit area that is applied to rock. A rock’s response to stress depends on many factors. The factors include the type of rock, the surrounding temperature and pressure, the type of stress, and the length of time the rock is under stress. In response to stress, rocks may either deform (change shape) or fracture (break). If stress is removed from rocks that have deformed, they may or may not return to their original shape. If they do return to their original shape, the change in shape is called elastic deformation. If they do not return to their original shape, the change in shape is called plastic deformation.    

Four types of stress that can act on rock are: confining stress, compression, tension, and shear.    
- Confining stress is stress that is applied to a deeply buried rock by the weight of all the material above it.    
Because the rock cannot move, it cannot deform or fracture.    
- Compression is stress that squeezes rocks together. It causes rocks to deform by folding or to fracture.    
Compression is the major type of stress at convergent plate boundaries.    
- Tension is stress that pulls rocks apart. Rocks under tension lengthen or break apart. Tension is the major type of stress at divergent plate boundaries.    
- Shear is stress that occurs when forces are parallel but applied in opposite directions. Shear stress is the major type of stress at transform plate boundaries.