Lab 2: The Interior of the Earth
Key Q: What is the interior of the Earth
like?
Part A: Observing Waves &
Measuring Wave Speed
In our lab activity you learned that waves travel at
a constant speed. Scientists cannot observe
earthquake waves moving through the Earth in
the same way you can observe waves moving
through water. They can, however, record and
study the energy from the earthquake waves as
the waves arrive at a recording station
(seismograph station). They can use
information they record about
the waves to make models of
the interior of the Earth.
Part A: Observing Waves &
Measuring Wave Speed
Think about how what you studied relates to how
scientists make models of the inside of the
Earth. What part of your experiment
represented:
• Th earthquake releasing energy in the Earth?
• The movement of energy waves from the
earthquakes (seismic waves) in the Earth?
• The material in the Earth through which seismic
waves travel?
• The arrival of a seismic wave at a seismograph
station where earthquakes are detected?
Part A: Observing Waves &
Measuring Wave Speed
• Vibrations of the earths crust are earthquakes.
• When an earthquake occurs energy waves
radiate out in all directions. These waves are
called seismic waves.
• Scientist cannot see seismic waves traveling
through the Earth but they can detect them with
a seismograph.
• Seismologists, scientists that study
earthquakes, can use the information they
gather from studying these waves to make a
conceptual model of the interior of the earth
Part B: Kinds of Seismic Waves
• There are 3 kinds of seismic waves. Each
one travels at a constant speed and
creates a different movement.
• Studying these waves can allow scientists
to:
– Determine the amount of energy released by
an earthquake (magnitude)
– Determine the exact location of an earthquake
– Create a model of the interior of the Earth.
Part B: Kinds of Seismic Waves
• P-waves
– are the fastest moving waves.
– Cause particles to move back and forth in
place.
– Move through solids, liquids, and gases.
Part B: Kinds of Seismic Waves
• S-waves
– Move slower than P-waves.
– Cause particles in materials to move side to
side.
– Travel only through solids.
Part B: Kinds of Seismic Waves
• L-waves
– are the slowest moving waves.
– Cause the surface to rise and fall like ocean
waves.
– Cause the most damage.
– Travel through solids liquids, and gases.
Which wave…
•
•
•
•
•
•
•
•
•
•
Travel through gases?
Travel through liquids?
Travel through solids?
Fastest waves?
Surface waves?
Slowest waves?
Cause particles to move back & forth in place?
Cause particles to move side to side?
Cause the most damage?
Cause surface to rise and fall like ocean waves?
Seismologists: scientists that study earthquakes
Seismic waves: earthquake waves
Seismograph: Instrument that detects seismic waves.
Fault: Fracture zone
where rock has been
moved
Focus: area along the
fault where movement
first occurs
Epicenter: Point on
the earths surface
directly above the
focus.
Calculate the epicenter &
magnitude of an earthquake
http://www.sciencecourseware.org/virtualearthquake
/vquakeexecute.html
Part C: Refraction of Waves
• We learned that waves travel at a constant
speed when they travel through one kind
of material.
• A waves speed depends on what material
it is traveling through, so when the wave
(P-wave) crosses a boundary line between
2 different materials in the Earth it
REFRACTS.
Part C: Refraction of Waves
REFRACTION: The change in direction of a wave due to its
change in speed as it passes from one material to the next.
P-wave
wave speed
= 30cm/s
)
Greater
angle 60°
wave speed
= 1m/s
20° (
Boundary Line (between 2 layers of the Earth)
Angle of wave in relation
to the boundary line
changed due to change in
wave speed
/animations/animation.php?flash
_title=Shadow+Zone&flash_file=
shadowzone&flash_width=220&
flash_height=320
• Annimation from usgs kids of shadow zones ADD IT!
Part D: Refraction of Earthquake
Waves in the Earth
• P-waves
– CAN travel through the whole planet.
– Refract (change direction) at a boundary between the
different layers of the Earth
– We know they refract because the refraction creates
shadow zones. (an area on the Earths surface where
no seismic waves are received.)
• S-waves
– Can NOT travel through the whole planet.
– They can travel through the Crust & the Mantle but
STOP at the Outer Core because it is liquid & Swaves only travel through solids
Part D: Refraction of Earthquake
Waves in the Earth
• Shadow Zones:
– An area on the Earths surface where no
seismic waves are received.
– Caused by the refraction of waves.
– Shows that the earth has layers.
Layers of the
Earth
Crust: cool layer of rigid
rock
Lithosphere: rigid layer.
Includes the Crust & the
upper Mantle
Mantle: semi-rigid layer
Asthenosphere: Has
plasticity (the ability to
flow). lower portion of
Mantle
Outer Core: liquid layer.
S waves stop here.
Inner Core: solid