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Earthquakes
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What You Will Learn

You will learn about earthquakes and how they are measured.

You will learn :
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what tools are used to measure earthquakes
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what scientists learn from measuring earthquakes
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VOCABULARY:
 Earthquake
 Seismology
— the study of earthquakes
 Seismologist
— a scientist who studies earthquakes
 Epicenter
 Seismic Wave
 Seismometer
— a tool scientists use to measure the
strength of seismic waves
 Magnitude
 Richter
Scale
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Review:
 Lithosphere
 Tectonic
plates are large slabs of crust that move
on Earth's mantle.

Faults are fractures in Earth's crust.
Three Types of Faults
Strike-Slip
Thrust
Normal
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What are Earthquakes?
 Vibrations
in Earth's lithosphere caused by a
sudden release of energy.
 The
energy is released in the form of seismic
waves, or waves that travel through Earth.
+2 Locations:
 The
location below
Earth's surface where
an earthquake starts is
called the hypocenter.
 The
location on Earth's
surface directly above
the hypocenter is called
the epicenter.
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Seismic Waves
P
waves, ( "primary"
or "compression" )
waves.
S
 shake
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P
S
the ground
back and forth,
parallel to the
direction the
waves are traveling.
waves travel faster
than S waves
waves,
("secondary" or
"shear”) waves.
shake the ground up
and down,
perpendicular to the
direction the
waves are traveling.
waves are more
destructive
Primary
Waves
(P
Waves)
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•
•
A type of seismic wave that compresses and expands the
ground
The first wave to arrive at an earthquake
Secondary
Waves
(S
Waves)
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A type of seismic wave that moves the ground up and down or
side to side
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Comparing Seismic Waves
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Surface Waves
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Move along the Earth’s surface
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Produces motion in the upper crust
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Motion can be up and down
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Motion can be around
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Motion can be back and forth
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Travel more slowly than S and P waves
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More destructive
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Seismographs,
("seismometers,”)
Measuring
instruments
used to
Earthquakes:
record
earthquakes.
Seismograms - the
recordings made by
the instruments.
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Typical Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
+ Measuring Earthquakes: Seismograms
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Scientists use seismograms to determine the sizes of
earthquakes.
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Magnitude: the size of an earthquake
-a measurement of the amount of energy released during an
earthquake.
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Richter Scale: a mathematical formula that assigns numbers
to earthquakes. (size of the earthquake)
+How do scientists calculate how far a location is
from the epicenter of an earthquake?
•
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Scientists calculate the difference between arrival times of
the P waves and S waves
The further away an earthquake is, the greater the time
between the arrival of the P waves and the S waves
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Richter Scale:
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logarithmic, meaning that a difference of one unit
represents a tenfold difference in size. For example, an
earthquake measuring 5.0 on the Richter scale is 10 times
larger than an earthquake measuring 4.0, 100 times larger
than an earthquake measuring 3.0, 1000 times larger than an
earthquake measuring 2.0, and so on.
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Locating
Earthquakes:
 Triangulation-a
triangle has three
sides, and it takes
three different
seismographs to find
the location of
an earthquake's
epicenter.
 The
location
where the three
circles intersect, or
cross each other, is
the epicenter.
+ Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
+ Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
+ Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM