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Ch. 19
Vocabulary
Term | Definition |
---|---|
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. |
epicenter | point on Earth's surface directly above the focus of an earthquake. |
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, horizontal shear, or horizontal tension. |
focus | point of the initial fault rupture where an earthquake originates that usually lies at least several kilometers beneath Earth's surface. |
plastic deformation | permanent deformation caused by strain when stress exceeds a certain value. |
primary wave | seismic wave that squeezes and pushes rocks in the same direction that the wave travels, known as 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. |
seismic wave | the vibrations of the ground during an earthquake. |
strain | deformation of materials in response to stress. |
stress | forces per unit area that act on a material-compression, tension, shear. |
seismogram | record produced by a seismometer that can provide individual tracking of each type of seismic wave. |
seismometer | instrument used to measure horizontal or vertical motion during an earthquake. |
amplitude | the size of the seismic wave; an increase of 1 in the scale represents an increase in amplitude of a factor of 10. |
magnitude | measure of the energy released during an earthquake, which can be described using the Richter scale. |
modified Mercalli scale | measures earthquakes intensity on a scale from I to XII; the higher the number, the greater the damage the earthquake has caused. |
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. |
Richter scale | numerical rating system used to measure the amount of energy released during an earthquake. |
seismic gap | place along an active fault that has not experienced an earthquake for a long time. |
soil liquefaction | process associated with seismic vibrations that occur in areas of sand that is nearly saturated; resulting in 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. |