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Earthquakes
Term | Definition |
---|---|
Earthquake | The shaking and trembling that results from the movement of rock beneath Earth's surface. |
Stress | A force that acts on rock to change its shape or volume. |
Shearing | A type of stress that can cause rock to break and slip apart or to change its shape. |
Tension | A stress force that pulls on the crust, stretching rock so that it becomes thinner in the middle. |
Compression | A stress force that squeezes rock until it folds or breaks. |
Deformation | Any change in the volume or shape of Earth's crust. |
Fault | A break in Earth's crust where slabs of crust slip past each other (occur along plate boundaries). |
Strike-slip fault | A type of fault, caused by shearing, where rocks on either side move past each other sideways with little up-or-down movement. |
Normal fault | A type of fault, caused by tension, where the fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault. |
Hanging wall | The half of the fault that lies above. |
Footwall | The half of the fault that lies below. |
Reverse fault | A type of fault, caused by compression, where the blocks move in opposite directions. |
Fault-block mountain | A mountain that forms where a normal fault uplifts a block of rock. |
Folds | Bends in rock that form when compression shortens and thickens part of Earth's crust. |
Anticline | A fold in rock that bends upward into an arch. |
Syncline | A fold in rock that bends downward in the middle to form a bowl. |
Plateau | A large area of flat land elevated high above sea level. |
Focus | The point beneath Earth's surface where rock that is under stress breaks, triggering an earthquake. |
Epicenter | The point on the surface directly above the focus. |
P waves (Primary waves) | Earthquake waves that compress and expand the ground like an accordion-cause buildings to contract and expand. |
S waves (Secondary waves) | Earthquake waves that vibrate from side to side as well as up and down- shake structures violently. |
Surface waves | Earthquake waves that move more slowly than P and S waves, but produce the most severe ground movements. |
Seismograph | A device that records the ground movements caused by seismic waves as they move through the Earth. |
Magnitude | A measurement of earthquake strength based on seismic waves and movement along faults. |
Mercalli scale | A scale that rates earthquakes according to their intensity and how much damage they cause. |
Richter scale | A rating of the size of seismic waves as measured by a particular type of mechanical seismograph. |
Liquefacation | The process by which an earthquake's violent movement suddenly turns loose soil into liquid mud. |
Aftershock | An earthquake that occurs after a larger earthquake in the same area. |
Tsunami | A large wave produced by an earthquake on the ocean floor. |
Base-isolated building | A building mounted on bearings designed to absorb the energy of an earthquake. |