1. EARTHQAUKES

2. EARTHQUAKE
• An earthquake is a shaking of the ground
caused by the sudden breaking and
movement of large sections (tectonic plates)
of the earth's rocky outermost crust. The
edges of the tectonic plates are marked by
faults (or fractures). Most earthquakes occur
along the fault lines when the plates slide
past each other or collide against each other.

3. 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.

4. • 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.

5. Fault or fault plane = the surface where when two blocks of the
earth suddenly slip past one another
Hypocenter = the location below the earth’s surface where the
earthquake starts
Epicenter = the location on the surface of the earth directly above
the hypocenter

6. 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.

7. 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.

8. What is a seismograph?
• A seismograph is an instrument used for
recording the intensity and duration of an
earthquake.

9. 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!

10. THE END…