Chapter 8Sections 1-4 By: Kelsey Garrison Brittany Ramsey
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 • Thon the Earth’s e point surface directly above an earthquakes starting point. • The most common method by which seismologists find an earthquake’s epicenter is the
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.