| Term | Definition |
|---|
| Earthquake | A movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move. |
| Elastic rebound | The sudden return of elastically deformed rock to its undeformed shape. |
| Focus | The location within Earth along a fault at which the first motion of an earthquake occurs. |
| Epicenter | The point on Earth's surface directly above an earthquake's starting point (or focus). |
| Body wave | In geology, a seismic wave that travels through the body of a medium. |
| Surface wave | In geology, a seismic wave that travels along the surface of a medium and that has a stronger effect near the surface of the medium than it has in the interior. |
| P wave | Also known as "primary/compression waves". P waves are seismic waves that cause particles of rock to move in a back-and-forth direction that is parallel to the direction in which the waves are traveling. P waves are faster than S waves and can travel through solids, liquids, and gases. |
| S wave | Also known as "secondary/shear waves". S waves are the second-fastest seismic waves and arrive at detection sites right after the P waves come in. S waves cause particles of rock to move in a side-to-side direction that is perpendicular to the direction in which the waves are traveling. |
| Love wave | Another surface wave that causes rocks to move side-to-side. |
| Rayleigh wave | Another surface wave that cause the ground to move with an elliptical, rolling motion. |
| Shadow zone | An area of Earth's surface where no direct seismic waves form a particular earthquake can be detected. |
| Fault zone | A region of numerous, closely spaced faults. |
| Seismograph | An instrument that records vibrations in the ground. |
| Seismogram | A tracing of an earthquake motion that is recorded by a seismograph. |
| Magnitude | A measure of the strength of an earthquake. |
| Richter scale | A chart that measures the amount of ground motion caused by an earthquake. |
| Moment magnitude | A measurement of earthquake strength based on the size of the area of the fault that moves, the average distance that the fault blocks move, and the rigidity of the rocks in the fault zone. |
| Intensity | In Earth science, the amount of damage caused by an earthquake. |
| Mercalli scale | Another scale used by seismologists to rate an earthquake's intensity using the Roman numerals I-XII (1-12). |
| Tsunami | A giant ocean wave that forms after a volcanic eruption, submarine earthquake, or landslide. |
| Seismic gap | An area along a fault where relatively few earthquakes have occurred recently but where strong earthquakes are known to have occurred in the past. |
| Foreshock | A little earthquake that might preceed a larger one. |
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