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fault

Surface along which rocks move when they pass their elastic limit and break.

earthquake

Vibrations produced when rocks break along a fault.

normal Fault

Break in rock caused by tension forces, whrer rock above the fault surface moves down relative to the rock below the fault surface.

reverse fault

Break in rock caused by compressive forces, where rock above the fault surface moves upward relative to the rock below the fault surface.

strike-strip fault

Break in rock caused by shear forces, where rocks move past each other without much vertical movement.

seismic wave

wave generated by an earthquake.

focus

In an earthquake, the point below Earth's surface where energy is released in the form of seismic waves.

primary wave

Seismic wave that moves rock particles back-and-forth in the same direction that the wave travels.

secondary wave

seismic wave that moves rock particles at right angles to the direction of the wave.

surface wave

Seismic wave that moves rock particles up-and-down in a backward rolling motion and side-to-side in a swaying motion.

epicenter

Point on Earth's surface directly above an earthquake's focus.

seismograph

instrument used to register earthquake waves and record the time that each arrived

magnitude

measure of the energy released during an earthquake

liquefaction

occurs when wet soil acts more like a liquid during an earthquake

tsunamis

Seismic sea wave that begins over an earthquake focus and can be highly destructive when it crashes on shore

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