Seismology The study of earthquakes. The scientists who study the earthquakes are called seismologists.
Fault A break in the Earth’s crust along which blocks of the crust slide relative to one another. Earthquakes occur along faults due to this sliding.
Deformation The change in the shape of a rock in response to stress. Rock along a fault deforms mainly in two ways-in a plastic manner, like a piece of molded clay, or in a n elastic manner, like a rubber band.
Elastic rebound The sudden return of elastically deformed rock to its original shape. Elastic rebound occurs when more stress is applied to rock than the rock can withstand.
Seismic waves Waves of energy that travel through the earth. Different types of seismic waves travel at different speeds and move the materials that they travel through differently.
P waves Travel through solids, liquids, and gases-fastest seismic waves. Because p waves are always the first seismic waves to be detected, they are also called primary waves.
S waves Shear waves-second fastest seismic wave. Also, S waves are slower than P waves and always arrive second; thus, they are also called secondary waves.
Seismographs Are instruments located at or near the surface of the earth that record seismic waves.
Seismogram A tracing of earthquake motion created by a seismograph. Seismologists use seismograms to calculate when an earthquake started.
Epicenter The point on the Earth’s surface directly above an earthquakes starting point. The most common method by which seismologists find an earthquake’s epicenter is the s-p-time method.
Focus The point inside the Earth where an earthquake begins.
Gap hypothesis States that sections of active faults that have had relatively few earthquakes are likely to be the sites of strong earthquakes in the future.
Seismic gaps The areas along a fault where relatively few earthquakes have occurred.
Moho A place within the Earth where the speed of seismic waves increases sharply. It marks the boundary between the Earth’s crust and mantle.
Shadow zone An area on the Earth’s surface where no direct seismic waves from a particular earthquakes can be detected.