| A | B |
|---|
| Earthquake | the vibration of Earth produced by the rapid release of energy, often caused by slippage along a break in EarthÕs crust |
| Focus | the point within Earth where the earthquake starts |
| Epicenter | the location on the surface directly above the focus |
| Fault | fractures in Earth where movement has occurred |
| Elastic rebound hypothesis | an explanation for a possible cause of earthquakes; it says that when rocks are deformed, they first bend, then break, releasing stored energy as they snap back to their original shape |
| Aftershock | smaller earthquakes following a major earthquake |
| Foreshock | smaller earthquakes that often come before a major earthquake |
| Siesmograph | instruments that record earthquake waves |
| Siesmogram | the record made by a seismograph |
| Surface wave | seismic waves that travel along EarthÕs outer layer |
| P wave | earthquake waves that pushes and pulls rocks in the direction of the wave; also known as a compression wave |
| S wave | a seismic wave that shakes particles perpendicular to the direction the wave is travelling |
| Moment magnitude | a measure of earthquake magnitude, derived from the amount of displacement that occurs along a fault zone and estimates the amount of energy released by the earthquake |
| Liquefaction | a phenomenon in which soils and other unconsolidated materials saturated with water are turned into a liquid that is not able to support buildings |
| Tsunami | a seismic sea wave |
| Seismic gap | an area along a fault where there has not been any earthquake activity for a long period of time |
| Crust | the thin, rocky outer layer of Earth |
| Mantle | the 2890-km-thick layer of Earth located below the crust |
| Lithosphere | the rigid outer layer of Earth, which includes the crust and the upper mantle |
| Asthenosphere | a weak plastic-like layer of the mantle situated below the lithosphere; the rock within this zone is easily deformed |
| Outer core | a layer beneath the mantle that contains liquid iron and generates EarthÕs magnetic field |
| Inner core | the solid, innermost layer of Earth |
| Moho | the boundary separating the crust from the mantle; distinguished by an increase in the velocity of seismic waves |
