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 Earthquakes
What is an Earthquakes?
 Earthquakes are the shaking,
rolling or sudden shock of the earth’s surface. They are the Earth's
natural means of releasing stress. More than a million earthquakes rattle the
world each year. The West Coast is most at risk of having an earthquake, but
earthquakes can happen in the Midwest and along the East Coast. Earthquakes can
be felt over large areas although they usually last less than one minute.
Earthquakes cannot be predicted - although scientists are working on it!
What causes an Earthquake?
 There are about 20 plates along the surface of the earth
that move continuously and slowly past each other. When the plates squeeze or
stretch, huge rocks form at their edges and the rocks shift with great force,
causing an earthquake. Think of it this way: Imagine holding a pencil
horizontally. If you were to apply a force to both ends of the pencil by
pushing down on them, you would see the pencil bend. After enough force was
applied, the pencil would break in the middle, releasing the stress you have
put on it. The Earth's crust acts in the same way. As the plates move they put
forces on themselves and each other. When the force is large enough, the crust
is forced to break. When the break occurs, the stress is released as energy
which moves through the Earth in the form of waves, which we feel and call an
earthquake.
What is a Fault?
  A fault is an area of stress in the earth where broken
rocks slide past each other, causing a crack in the Earth's surface. There are
the major types of faults: dip-slip normal, dip-slip reverse, strike-slip, and
oblique-slip.
What are plate tectonics?
 The theory of plate tectonics is a interesting story of
continents drifting from place to place breaking apart, colliding, and grinding
against each other. The plate tectonic theory is supported by a wide range of
evidence that considers the earth's crust and upper mantle to be composed of
several large, thin, relatively rigid plates that move relative to one another.
(See plate tectonic graphic above.) The plates are all moving in different
directions and at different speeds. Sometimes the plates crash together, pull
apart or sideswipe each other. When this happens, it commonly results in
earthquakes.
 What is a seismograph?
A seismograph is an instrument used for recording the intensity and duration of
an earthquake.
What is a Tsunami?
 A tsunami is a large ocean wave usually caused by an underwater earthquake or a
volcanic explosion. Tsunamis are NOT tidal waves. Tidal waves are caused by the forces of the moon, sun, and planets upon the tides, as well as the wind as it
moves over the water. With typical waves, water flows in circles, but with a
tsunami, water flows straight. This is why tsunamis cause so much damage!
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