earthquake
the shaking and trembling that results from the movement of rock beneath Earth's surface
focus
the point beneath Earth's surface where rock under stress breaks to cause an earthquake
epicenter
the point of the surface directly above the focus
seismic waves
carry the energy of an earthquake away from the focus, through Earth's interior, and across the surface.
types of body waves
compressional and shear waves
compressional waves
sometimes called primary waves. Compress and expand the ground like an accordion.
shear waves
sometimes called secondary waves. Vibrate from side to side and up and down.
surface waves
move more slowly than P and S waves. Cause most damage.
P waves
move the most quickly and can go through anything.
S waves
arrive after primary waves and shake buildings from side to side.
types of scales for measuring earthquakes
Mercalli, Richter, and moment magnitude scale.
seismograph
records ground movements caused by seismic waves as they move through the Earth
fault
a fracture, or break in the Earth's lithosphere, along which blocks of rock move past each other.
stress
the force exerted when an object presses on, pulls on, or pushes against another object.
80%
percentage of earthquakes that occur in a belt around the edge of the Pacific Ocean
lithosphere
where all earthquakes occur
three
main types of faults
normal fault
the block of a rock above the fault plane slides down relative to the other blocks. Boundaries that are moving apart.
reverse fault
the block of rock above the fault plane moves up relative to the other block. Near boundaries that are coming together.
strike slip fault
blocks of rock move sideways on either side of the fault plane. Near where plates scrape against each other
hanging wall
the surface of block that is on top of the plane of the fault.
foot wall
the surface or block that lies below the plane of the fault.
strike
the direction in which the fault runs.
dip
the direction is perpendicular to the strike direction.
amplitude
is the height (on paper) of the strongest wave.
magnitude
the strength of an earthquake.
seismogram
the recording produced by a seismograph.
friction
is the force that opposes the motion of one surface as it moves across another surface. When this is high, the rocks lock together, stress builds until an earthquake occurs.
tilt meter
measures tilting or raising of the ground.
creep meter
uses a wire stretched across a fault to measure horizontal movement of the ground.
laser-ranging device
uses a laster beam to detech horizontal fault movements.
GPS
helps scientists monitor changes in elevation as well as horizontal movement along faults.
anticline
an upward fold in rock formed by compression of Earth's crust
syncline
a downward fold in rock formed by compression in earth's crust.