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Chapter 19 Vocab.
Term | Definition |
---|---|
stress | forces per unit area that act on a material - compression, tension, and shear. |
strain | deformation of materials in response to stress |
elastic deformation | causes materials to bend and stretch; proportional to stress, so if the stress is reduced or returns to zero the strain or deformation is reduced or disappears. |
plastic deformation | permanent deformation caused by strain when stress exceeds a certain value. |
fault | fracture or system of fractures in Earth's crust that occurs when stress is applied too quickly or stress is too great; can form as a result of horizontal compression (reverse fault), horizontal shear (strike-slip fault), or horizontal tension (normal fau |
seismic wave | the vibrations of the ground during an earthquake. |
primary wave | seismic wave that squeezes and pushes rocks in the same direction that the wave travels, known as a P-wave. |
secondary wave | seismic wave that causes rock particles to move at right angles to the direction of the wave, known as an S-wave. |
focus | point of the initial fault rupture were an earthquake originates that usually lies at least several kilometers beneath Earth's surface. |
epicenter | point on Earth's surface directly above the focus of an earthquake. |
seismometer | instrument used to measure horizontal or vertical motion during an earthquake. |
seismogram | record produced by a seismometer that can provide individual tracking of each type of seismic wave. |
Richter scale | numerical rating system used to measure the amount of energy released during an earthquake. |
magnitude | measure of the energy released during an earthquake, which can be described using the Richter scale. |
amplitude | the size of the seismic waves; an increase of 1 in the scale represents an increase in amplitude of a factor of 10. |
moment magnitude scale | scale used to measure earthquake magnitude - taking into account the size of the fault rupture, the rocks' stiffness, and amount of movement along the fault - using values that can be estimated from the size of several types of seismic waves. |
modified Mercalli scale | measures earthquake intensity on a scale from I to XII; the higher the number, the greater the damage the earthquake has caused. |
soil liquefaction | process associated with seismic vibrations that occur in areas of and that is nearly saturated; resulting the ground behaving like a liquid. |
tsunami | large, powerful ocean wave generated by the vertical motions of the seafloor during an earthquake; in shallow water, can form huge, fast-moving breakers exceeding 30 m in height that can damage coastal areas. |
seismic gap | place along an active fault that has not experienced an earthquake for along time. |