Earthquake Faulting

The triggering mechanism for earthquakes involves rock deformation. The deformation of a solid material may be classified into three categories: If the amount of stress is less than what is called the elastic limit, the solid changes it size or shape or both, that is, the solid is strained. If the stress is later removed, the strain disappears and the solid returns to its original shape and size. This is elastic deformation. If the elastic limit is surpassed, the material flows plastically. Rocks at depth are deformed in this manner due to high temperature and confining pressure. A solid thus deformed does not return to its original size and shape even when the stress is removed. Near the earth’s surface, if the plastic limit is exceeded, rocks fail by rupturing. The ability to resist rupturing depends upon the rock’s strength, temperature, confining pressure, presence of fluids, etc.