Research Rack: Glossary

amplitude - half of the up-and-down extent of a wave’s vibration

convergent boundary - in plate tectonics, the boundary between two plates that are converging (moving toward each other)

divergent boundary - in plate tectonics, the boundary between two plates that are diverging (spreading apart)

earthquake - a shaking or trembling of the ground that is volcanic or tectonic in origin

epicenter - the point on Earth’s surface directly above an earthquake’s focus

fault - a large break in rocks, from several meters to many kilometers long, where rocks not only crack but also move along either side of the break

normal fault - a pull-apart (tension) fracture in rocks, where rocks that are above the fault surface drop downward in relation to rocks that are below the fault surface

plate tectonics - the theory that Earth’s crust and upper mantle exist in sections called plates and that these plates slowly move around on the mantle

primary (P) waves - waves of energy, released during an earthquake that travel the fastest through Earth by compressing particles in rocks in the same direction the wave is traveling

reverse fault - a compression fracture in rocks, where rocks that are above the fault surface are forced up over rocks that are below the fault surface

secondary (S) waves - waves of energy, released during an earthquake, that travel through the Earth by moving particles in rocks at right angles to the direction the wave is traveling

seismogram - the record of an earth tremor as made by a seismograph

seismograph - an instrument that records earthquake waves

seismologist - a scientist who studies earthquakes and waves

strike-slip fault - a break in rocks where rocks on either side of the fault move past each other (instead of above or below each other)

surface wave - waves of energy, released during an earthquake, that reach Earth’s surface and travel outward from the epicenter in all directions

transform boundary - in plate tectonics, a boundary between tow plates that are sliding past one another

triangulation - the method in surveying of making measurements and using trigonometry to find where places are located on the earth's surface using points whose exact location is known.

tsunami - a great sea wave produced by an earthquake or volcano eruption under the sea and also known as a tidal wave

Zulu time (Z) - One of several names for the 24-hour time that is used throughout the scientific and military communities. Other names for this time measurement are Universal Time Coordinate (UTC) or Greenwich Mean Time (GMT).