| A | B |
|---|
| Earthquake | A series of low frequency seismic or earth waves, somewhat like sound waves. |
| stress | Any force exerted on the matter in an object. |
| compression | Forces or stresses that act to squeeze or crush an object or substance. |
| tension | Forces or stresses that act to pull an object or substance apart. |
| shear | Forces or stresses acting in opposite directions on different parts of the same object or substance. |
| divergent boundary | Margin between two tectonic plates that are moving away from each other or diverging which are sea floor spreading origins and rift valleys. |
| convergent boundary | Margin between two tectonic plates that are moving toward each other or converging. |
| transform boundary | Margin between two tectonic plates that are sliding in opposite directions parallel to the margin. |
| strain | Change in the shape of a solid due to stresses exerted on the material. |
| joint | Stress crack in a rock that shows no indications of motion of the rock on either side of the crack. |
| fault | Crack or joint in rock where the rock on both sides of the joint have moved relative to each other. |
| strike | Compass direction of an imaginary line drawn horizontally on the surface of a fault face or rock stratum. |
| dip | Angle of slope of a fault face or stratum, measured from the horizontal plane to the fault or stratum surface, measured perpendicular to the strike of the surface. |
| dip slip fault | A fault whose main motion is parallel to its dip direction. |
| normal fault | A dip slip fault in which the body of rock above the fault surface drops relative to the body of rock underneath the fault surface. |
| reverse fault | Dip slip fault in which the upper body of rock slides upward relative to the lower body of rock. |
| strike slip fault | A fault along which the main movement is horizontal, or parallel to the fault's strike. "transform fault" |
| seismometer | Instrument that detects earthquake waves. |
| P wave | First earthquake wave that reaches a seismic station from an earthquake, fastest of seismic waves. |
| S wave | Second earthquake wave that reaches a seismic station from an earthquake. |
| surface wave | One of various earthquake waves that travel only along the surface of the earth. Slower and more damaging than S and P |
| focus | Actual center of an earthquake's activity deep underground. |
| epicenter | Point on the earth's surface directly above the place within the earth where an earthquake actually occurs. |
| Richter scale | Familiar system of reporting the magnitude or energy of an earthquake. |
| magnitude | The size or intensity of some measurable quantity . |
| intensity | Measure of the concentration of energy expended or the effects of energy released. |
| tsunami | Far reaching, devastating water wave caused by seismic activity. |
