earthquake
a movement / trembling of the ground that is caused by a sudden release of energy when rocks along a fault move
elastic rebound
the sudden return of elastically deformed rock to its undeformed shape
focus
the location within Earth along a fault at which the first motion of an earthquake occurs
epicenter
the point on Earth's surface directly above the focus
body wave
a seismic wave that travels through the body of a medium
surface wave
a seismic wave that travels along the surface of a medium and has a stronger effect near the surface of the medium that it has in the interior
P wave
primary or compression wave; causes particles to move back-and-forth parallel to the direction in which the wave is moving; can move through solid and liquid
S wave
secondary or shear wave; causes particles to move side-to-side, perpendicular to the direction in which the wave is moving; can move through only solid
shadow zone
an area on Earth's surface where no direct seismic waves from a particular earthquake can be detected
fault zone
a region of numerous, closely spaced faults
seismograph
an instrument that records vibrations in the ground
seismogram
a tracing of earthquake motion that is recorded by a seismograph
magnitude
a measure of the strength of an earthquake
intensity
the amount of damage caused by an earthquake
tsunami
a giant ocean wace that forms after a volcanic eruption, submarine earthquake, or landslide
seismic gap
an area along a fault where relatively few earthquakes have occured recently but where strong earthquakes are known to have occured in the past
magma
liquid rock produced under Earth's surface
volcanism
any activity that includes the movement of magma toward or onto Earth's surface
lava
magma that flows onto Earth's surface; the rock that forms when lava cools and solidifies
volcano
a vent or fissure in Earth's surface through which magma and gases are expelled
hot spot
a volcanically active area of Earth's surface, commonly far from a tectonic plate boundary
mafic lava
igneous rock that is rich in magnesium and iron; dark
felsic lava
igneous rock that is rich in feldspars and silica; light
pyroclastic material
fragments of rock that form during a volcanic eruption; volcanic dust, volcanic ash, lapilli, volcanic bombs, and volcanic blocks
caldera
a large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink