Download Types of Earthquake Waves

Research
There are forces within the earth that are bending and straining
the relatively thin crust we call home. Although scientists and
engineers do not full understand these forces, we know that
they cause the earth’s crust to bend until it snaps. This action
is called an earthquake. Earthquakes can cause extensive
damage to building, roadways, and infrastructure. That is why
there are research teams that focus on earthquakes and
designs for buildings that can help withstand the forces that can
dome from the earth’s crust. Therefore for you to design and
build your tower, you will research earthquake and engineering
design terms throughout this presentation.
Earthquake Terms
 Please
read the following
slides. As you read, fill out the
Science and Technology Work
Book titled,
“Epicenter Towers.”
Earthquakes
Engineers and scientists
have been studying
earthquakes and the
effects that they have on
structures for years.
Together, they are
working on construction
techniques to reduce
damage caused by forces
within the earth.
Measuring Earthquakes

Scientists called seismologists
use a machine called a
seismograph to measure
earthquakes. When an
earthquake strikes, it shakes
the bedrock which the
seismograph is attached to,
causing the pen to move while
the paper remains still, thus
making a jagged line.
Seismologists then read the
seismogram and interpret the
intensity of the earthquake.
Measuring Earthquakes

Scientists use a method of measurement called
the Richter Scale to describe the magnitude
(strength) of an earthquake. The scale starts at
zero and goes as high as necessary. Each
number on the scale represents an earthquake
with about 30 times more power than the
previous number. Therefore, an earthquake that
registers a “7” on the Richter Scale would be 30
times more powerful than one that registered a
“6.” Therefore the higher the number on the
Richter Scale, the higher the magnitude.
Types of Earthquake Waves

Knowing the characteristics of earthquake
waves help geologists determine the
locations of earthquakes and the
characteristics of the earth’s layers. This
information is fundamental to the
development of earthquake resistant
structures.
Types of Earthquake Waves
There are three types of earthquake waves:
 Primary Waves (P waves)
 Secondary Waves (S waves)
 Surface Waves
Watch the following illustration to help you understand how
P waves and S waves work.
The Slinky and The Rope
Earthquakes generate several kinds of seismic waves
including P, for "Primary" and S, for "Secondary" waves.
P Waves
The P waves move in a compressional motion similar to the
motion of a slinky, while the S waves move in a shear
motion perpendicular to the direction the wave is travelling.
S Waves
Primary Waves
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The fastest of all three types of waves
P waves travel between 5 and 13 km/second
Represented by the compression waves of the slinky on
the previous slide.
Can pass through liquids, solids and gasses
Expand and compress materials in their path
Move buildings back and forth
The compression causes a slight vibration that would
rattle dishes, or shake any unstable objects
These waves warn people that an earthquake is
happening and can give people time to prepare for the
movement to come.
On a seismograph, p waves appear as a smooth up and
down line.
Secondary Waves
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Travel slower than P waves.
Their velocity is about 55% of the related P wave
Represented by the movement of a rope
Can pass through only solids, not liquids or
gasses
S waves shake buildings up and down and from
side to side
On a seismograph, S waves appear on as
jagged up and down lines
Surface Waves
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The slowest wave of all
Travel along the earth’s surface
Their rolling motion (much like an ocean wave)
breaks up roads and buildings thus causing the
most structural damage
They cause part of a building to move up, while
another part of the building is moving down
Please click the following to see how earthquake
waves appear on a seismograph:
How Do I Read a Seismograph?
P and S Waves Illustration

Click on the following link that illustrates
how both primary and secondary waves
affect the earth’s surface.
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Observe animations of earthquake waves.
Time
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The length of time between the arrival of P
and S waves gives an indication to the
origin of the earthquake. The shorter the
time the closer the focus of the earthquake
is.
Focus
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The focus is the location at which the
energy of an earthquake is released and
waves originate.
Earthquakes generally occur at depths
around 30 km but may occur at depths of
600 km or more.
Epicenter
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The epicenter is the point on Earth’s
surface directly above the focus of an
earthquake. The strongest shaking often
occurs at this point.
Conclusion

You have just learned and studied
earthquakes and how they can affect the
surface of the earth. Your task will be to
design and construct a tower that can
withstand the intensity of an earthquake.
As you have learned, background
knowledge is the key to efficient design
and construction. Hopefully, this
presentation will help you to defeat the
“epicenter tower eliminator.”
Are you up to the challenge?