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Glossary
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Below you will find key words and concepts that you should remember from this chapter.
aftershock  Small earthquake that follows a main shock.
(See page(s) 173)
Benioff zone  Distinct earthquake zone that begins at an oceanic trench and slopes landward and downward into Earth at an angle of about 30° to 60°.
(See page(s) 177)
body wave  Seismic wave that travels through Earth’s interior.
(See page(s) 161)
circum-Pacific belt  Major belt around the edge of the Pacific Ocean on which most composite volcanoes are located and where many earthquakes occur.
(See page(s) 177)
depth of focus  Distance between the focus and the epicenter of an earthquake.
(See page(s) 164)
earthquake  A trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath the surface.
(See page(s) 160)
elastic rebound theory  The sudden release of progressively stored strain in rocks results in movement along a fault.
(See page(s) 161)
epicenter  The point on Earth’s surface directly above the focus of an earthquake.
(See page(s) 161)
focus  The point within Earth from which seismic waves originate in an earthquake.
(See page(s) 161)
intensity  A measure of an earthquake’s size by its effect on people and buildings.
(See page(s) 166)
island arc  A curved line of islands.
(See page(s) 177)
Love wave  A type of surface seismic wave that causes the ground to move side to side in a horizontal plane perpendicular to the direction the wave is traveling.
(See page(s) 163)
magnitude  A measure of the energy released during an earthquake.
(See page(s) 166)
Mediterranean-Himalayan belt  A major concentration of earthquakes and composite volcanoes that runs through the Mediterranean Sea, crosses the Mideast and the Himalaya, and passes through the East Indies.
(See page(s) 177)
modified Mercalli scale  Scale expressing intensities of earthquakes (judged on amount of damage done) in Roman numerals ranging from I to XII.
(See page(s) 166)
moment magnitude  An earthquake magnitude calculated from the strength of the rock, surface area of the fault rupture, and the amount of rock displacement along the fault.
(See page(s) 167)
P wave  A compressional wave (seismic wave) in which rock vibrates parallel to the direction of wave propagation.
(See page(s) 162)
Rayleigh wave  A type of surface seismic wave that behaves like a rolling ocean wave and causes the ground to move in an elliptical path.
(See page(s) 163)
Richter scale  A numerical scale of earthquake magnitudes.
(See page(s) 167)
seismic sea wave  See tsunami.
(See page(s) 173)
seismic wave  A wave of energy produced by an earthquake.
(See page(s) 160)
seismogram  Paper record of earth vibration.
(See page(s) 163)
seismograph  A seismometer with a recording device that produces a permanent record of Earth motion.
(See page(s) 163)
surface wave  A seismic wave that travels on Earth’s surface.
(See page(s) 161)
S wave  A seismic wave propagated by a shearing motion, which causes rock to vibrate perpendicular to the direction of wave propagation.
(See page(s) 162)
travel-time curve  A plot of seismic-wave arrival times against distance.
(See page(s) 164)
tsunami (seismic sea wave)  Huge ocean wave produced by displacement of the sea floor; also called seismic sea wave.
(See page(s) 173)







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