| A | B |
|---|
| fault | surface along which rocks break and move |
| earthquake | vibrations caused by breaking rocks along faults; most result from plates moving over, under, and past each other |
| normal fault | break in rock due to tension forces, where rock above the fault surface moves downward in relation to rock below the fault surface |
| reverse fault | break in rock due to compression forces, where rocks above the fault surface move upward and over the rocks below the fault surface |
| strike-slip fault | break in rock due to shearing forces, where rocks on either side of the fault surface move past each other with little upward or downward movement |
| seismic wave | energy waves that are produced at and travel outward from the earthquake focus |
| focus | in an earthquake, the point beneath Earth's surface where energy release occurs. |
| primary wave | waves that travel outward from an earthquake's focus and cause particles in rocks to move back and forth in the same direction the wave is moving |
| secondary wave | waves that travel outward from an earthquake's focus and move through Earth by causing particles in rocks to vibrate at right angles to the direction of the wave |
| epicenter | point on Earth's surface directly above an earthquake's focus |
| surface wave | waves of energy that reach Earth's surface during an earthquake, travel outward from the epicenter, and move rock particles up and down and side to side |
| inner core | very dense, solid center of Earth that is made mostly of iron with smaller amounts of oxygen, silicon, sulfur, or nickel |
| outer core | liquid core that surrounds Earth's solid inner core and that is made mostly of iron |
| mantle | largest layer inside Earth, lying directly above the outer core and that is made mostly of silicon, oxygen, magnesium and iron. |
| crust | Earth's outermost layer, which varies in thickness from about 5 km to 60 km and is separated from the mantle by the Moho discontinuity |
| seismologist | scientist who studies earthquakes and seismic waves |
| seismograph | device used by seismologists to record primary, secondary, and surface waves from earthquakes |
| magnitude | measure of the energy released by an earthquake |
| tsunami | powerful seismic sea wave that can travel thousands of kilometers in all directions and that begins over an earthquake focus |
