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Transcript
Seismic
Waves
An Earthquake begins
at the…
Focus: The point where
the energy is released
after elastic limit is
reached.
Epicenter: The point on
the surface of the Earth
directly above the focus.
Earthquakes
produce three types
of waves with
different behaviors
as they travel
through materials.
Primary (P) Waves:
Move out from the earthquake focus.
Travel the fastest of the 3 waves.
Travel twice as fast as secondary waves.
Move by causing particles in rocks to move
back and forth in the same direction that
the wave is traveling.
 Example: slinky
 Are bent and slowed when
they hit the outer core.
 Longitudinal wave
Blue



Secondary (S) Waves:
 Move out from the earthquake focus.
 Move slower than primary waves.
 Move by causing particles in rocks to move at
right angles to the direction of wave travel.
 Example: rope
 Cannot travel through liquids,
so they are stopped by the outer
core.
 Transverse Wave
Red-
Surface Waves:
 Form when P and S waves reach the
surface.
 Slowest Waves, Most destructive
 Can cause the ground to shake
making rock roll and sway from side
to side.
 Only travel
through crust
Seismograph:
instrument used to record the
energy released by an
earthquake. Recording time of
wave arrival.
Produces paper sheet called a
seismogram
A stationary pen traces a record of
vibrations
Seismograph Stations
P waves arrive first
S waves arrive second
Surface waves arrive last (slowest)
3 or more seismograph stations are
needed to determine the location of
the epicenter.
 When an epicenter is far from a
location, the p wave has more time to
put distance between it and the s and
surface waves.




Finding the epicenter...
 Each city
determines their
distance from the
epicenter.
 That distance is
used as the radius
of a circle.
 After 3 cities create
circles, where they
intersect is the
actual epicenter.
Because of the behavior of
these different waves…
Scientists have indirect evidence
for the solid inner core and liquid
outer core of the Earth.
Earthquake waves travel faster
through the mantle than through
the crust.
So, scientists know the mantle
is denser than the crust.
Shadow Zone Animation
 http://www.earthquake.gov/learning/
animations/animation.php?flash_title
=Shadow+Zone+Flash+Animation&fl
ash_file=shadowzone&flash_width=2
20&flash_height=300