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Seismic Waves cary, the energy off and
earthquake from the focus. Through
earth’s Interior and across the surface.
Seismic Waves
Seismic waves carry the energy of an earthquake
Detail
P waves
compress and
expand the
ground.
P waves move
the fastest!
Detail
S waves vibrate
from side to side
as well as up and
down.
S-waves move at
about ½ the speed
of P waves!
Detail
Surface waves
produce the most
severe ground
movements &
damage even
though they move
the slowest!.
How is the Size of Earthquakes
Measured?
• A seismograph is the the tool used to
measure the strength of an earthquakes
How is the Size of Earthquakes
Measured?
• The seismograph prints out a seismogram
that scientists read to determine the
strength of the quake.
How is the Size of Earthquakes
Measured?
• The data from the seismogram is
translated into a 1-10 rating. Each step in
the scale represents a tenfold increase in
the size of the quake!
How are Earthquakes Measured?
• Earthquakes are measured based on
three different scales.
• The first measures the actual size of the
quake.
• The second measures the effects or
damage of the quake.
• The third measures the total energy of the
quake.
Mercalli Scale
• Developed in early twentieth century
• Measures the strength of ground motion
• It is not precise as the ground motion can
cause different amount of damage at
different locations
Richter Scale
• Developed in 1930s
• Gives the rating of the size of seismic
waves
• Provides accurate movement for small,
nearby earthquakes
• Does not work well for large or distant
earthquakes
Moment Magnitude Scale
• Used today, as it is the most precise
• Used to rate earthquakes of all sizes, near
or far