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Types of Faults Rocks Move Along Faults • Fault: – Fracture, or break, in Earth’s lithosphere, where blocks of rock move past each other • At some parts of a fault, the rock slides slowly or constantly. At others it sticks or locks together. – Rock bends as stress is put on it (the force exerted when an object presses on, pulls on, or pushes against another object.) Earthquake • Earthquake – shaking of the ground caused by the sudden movement of large blocks of rock along a fault – can occur when there is a sudden release of stress in the lithosphere. • Release of stress occurs when the rocks break free from being stuck • Strength of an earthquake depends on – The amount of stress built up – The distance the rocks move along the fault The rocks that move • Most faults are along tectonic plate boundaries – Most earthquakes occur here • The rocks that move during an earthquake are smaller than tectonic plates • A small percentage of earthquakes occur along faults within plates – Stress along a plate boundary can cause the rocks to break and move along weak areas in the middle of the plate. Types of faults • Faults are classified base on how they move – How they move is determined by the kind of stress that they are under. • More than one type of fault may be present along the same boundary. Normal Fault • The block of rock above the fault plane slides down relative to the other block • Occurs when stress pulls the rocks apart • Earthquakes are common near boundaries where tectonic plates are moving apart – The Great Rift Valley of Africa. Reverse Fault • The block of rock above the fault plane moves up relative to the other block • Occurs when stress presses rocks together • Occurs near collisionzone boundaries between plates Strike Slip Faults • Blocks of rock move sideways on either side of the fault plane. • Occurs when stress pushed rocks horizontally • Happens when plates scrape past each other