earthquake
The vibration of Earth produced by the rapid release of energy.
focus
The point within Earth where an earthquake originates.
epicenter
The location on Earth's surface directly above the focus, or origin, of an earthquake.
fault
A fracture in Earth along which movement has occurred.
elastic rebound hypothesis
The explanation stating that when rocks are deformed, they break, releasing the stored energy that results in the vibrations of an earthquake.
aftershock
A small earthquake that follows the main earthquake.
foreshock
A small earthquake that often precedes a major earthquake.
seismograph
An instrument that records earthquake.
Seismogram
The record made by a seismograph.
surface wave
A seismic wave that travels along the surface of Earth.
P wave
Earthquake wave that pushes and pulls rocks in the direction of the wave.
S wave
A seismic wave that shakes particles perpendicular to the direction the wave is traveling.
moment magnitude
A more precise measure of earthquake magnitude than the Richter.
liquefacation
A phenomenon, sometimes associated with earthquakes, in which soils and other unconsolidated materials saturated with water are turned into a liquid that is not able to support buildings.
tsunami
The Japanese word for a seismic sea wave.
seismic gap
An area along a fault where there has not been any earthquake activity for a long period of time.
crust
The thin, rocky outer layer of Earth.
mantle
he 2890-kilometer-thick layer of Earth located below the crust.
lithosphere
The rigid outer layer of Earth, including the crust and upper mantle.
asthenosphere
A weak plastic layer of the mantle situated below the lithosphere.
outer core
A layer beneath the mantle about 2260 kilometers thick.
inner core
The solid innermost layer of Earth, about 1220 kilometers in radius.
Moho
The Mohorovicic discontinuity, which is shortened to Moho.