| 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 movements. |
| 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, and 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. it is made mostly of silicon, oxygen, magnesium, and iron. |
| Crust | Earth's outermost layer. |
| Seismologist | Scientist who studies earthquakes and seismic waves. |
| Seismograph | Device used 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. |
