| A | B |
|---|
| Focus | point beneath Earth's surface where rock that is under stress breaks, triggering an earthquake |
| Epicenter | The point on the surface directly above the focus. |
| Seismic Waves | The vibrations that travel through Earth carrying energy released during an Earthquake. |
| P waves | Primary Waves. The first waves to arrive at any given location. They compress and expand the ground like an accordian. Can travel through liquids and solids. |
| S waves | Secondary waves. Vibrate from side to side as well as up and down. Travels only through solids. |
| Surface waves | Move slower than P and S waves but produce the most severe ground movements. |
| Seismograph | Instrument that records the ground movements caused by seismic waves as they move through Earth. |
| Magnitude | A measurment of earthquake strength based on seismic waves and movements along faults. |
| Mercalli Scale | Rates earthquakes based on the affect of the earthquake on people, buildings, and the land surface. |
| Richter Scale | This scale rates the size of seismic waves and provides accurate measurements for small, nearby earthquakes. |
| Moment Magnitude Scale | A rating system that estimates the total energy released by an earthquake. |
