GLO ACADEMY® NEWS
E ARTHQUAKES G IVE C LUES
T O EARTH'S STRUCTURE
* SCIENTISTS USE WAVES TO EXAMINE THE
STRUCTURE OF EARTH'S INTERIOR *
The ground shakes, the earth moves, people run in
terror at the sound and fury of an earthquake! What
causes earthquakes? Why does the surface of our
planet tremble and threaten the peace?
When the ground shakes violently during an
earthquake, the vibrations caused by breaking rocks
spread in all directions like water waves spreading on a
pond. A wave is any disturbance that spreads through
space. Earthquake waves that spread through the
Earth are called seismic waves. They move through
the ground like sound waves move through the air and
water waves move through the ocean. The place where
an earthquake starts is called an epicenter. As earthquake waves spread through the ground they lose
energy and cause less shaking the farther they move
from the epicenter.
There are two basic types of seismic waves: body
waves and surface waves. Body waves spread fast and
deep below the surface of the Earth at depths of less
than 20 miles (about 31 kilometers) down. Body waves
reach speeds of 4 to 5 miles per second (about 6 to 7
kilometers per second). Body waves called P-waves and
S-waves cause the most damage. P-waves (also called
primary or compressional waves) push and pull rocks
and buildings apart and cause them to crush then break
apart. P-waves can travel through solids, liquids, or air.
S-waves (also called shear or transverse waves)
shake the ground from side to side and cause surface
structures to sway, crack, and tumble. Shear waves
only travel through solids.
Surface waves move slower than body waves
over the surface of the earth. They spread at
speeds of about 2 to 3 miles (3 to 4 kilometers) per
second and give people a slow rocking sensation that
usually does a small amount of damage.
Think about it …
How might maps come in handy in the
study of earthquakes?
Answer: Maps could come in handy to help
scientists keep records of earthquake activity.
These records would help them to study quakes
and understand what causes them.
All waves transfer energy from one place to another.
©2006, Global Learning Online Academy
UNIT TWO - LESSON ONE
MIDDLE GRADES SCIENCE
6
NAME:_______________________________________ DATE: __/__/__
UNIT TWO - LESSON #1
HOW DO WAVES MOVE?
Discuss the GLO ACADEMY® NEWS with your instructor then define the lesson vocabulary
terms in your own words.
wave:
_____________________________________________________________
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seismic wave: ________________________________________________________
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epicenter: __________________________________________________________
__________________________________________________________________
body wave: __________________________________________________________
__________________________________________________________________
surface wave: ________________________________________________________
__________________________________________________________________
P-wave (primary or compressional): _________________________________________
__________________________________________________________________
S-wave (shear or transverse):
____________________________________________
__________________________________________________________________
Select six of the terms you defined then draw a picture that conveys the
meaning of each term.
©2006, Global Learning Online Academy
MIDDLE GRADES SCIENCE
7
NAME:_______________________________________ DATE: __/__/__
USE A SLINKY TO EXAMINE THE MOTION OF WAVES
Place a slinky on a smooth flat surface. Have a friend hold on end of the slinky
while you hold the other.
Move your end of the slinky back and forth as shown by the arrows while your
partner holds their end in the same position. Draw how the slinky moved.
©2006, Global Learning Online Academy
MIDDLE GRADES SCIENCE
8
NAME:_______________________________________ DATE: __/__/__
Describe how the wavelike motion reached your friend's hand.
___________________________________________________________
___________________________________________________________
___________________________________________________________
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___________________________________________________________
___________________________________________________________
Compress one end of the slinky as shown. Then, release it. Draw how the slinky
moved.
Describe how the wavelike motion reached your friend's hand.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
©2006, Global Learning Online Academy
MIDDLE GRADES SCIENCE
9
NAME:_______________________________________ DATE: __/__/__
FINAL QUESTION
Write a short paragraph comparing the motion of the two waves. How did the
direction of the disturbance created by you --the side-to-side motion and the
compression -- change the way the wave moved from your end of the slinky to
your partner's end.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
Which slinky wave could be compared to a seismic P-wave? Explain your answer.
___________________________________________________________
___________________________________________________________
___________________________________________________________
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Which slinky wave could be compared to a seismic S-wave? Explain your answer.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
©2006, Global Learning Online Academy
MIDDLE GRADES SCIENCE
10