Transcript P Wave

Laboratory Manual
in Physical
Geology, 10e
Image PPTs
Chapter 16
Earthquake Hazards
and Human Risks
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Fig. 16.04
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Fig. 16.06
A seismograph measures relative
movement of the ground to a stationary
pen.
Fig. 16.07
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The Richter Scale is a logarithmic scale that measures the magnitude of an earthquake. A
magnitude 5.0 quake has Earth movements ten times greater than a 4.0 magnitude quake (=
~32x the energy released).
In theory, the local crust melts in a magnitude 10 or greater quake. The most energetic quake
recorded to date had a magnitude of approximately 9.0.
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Body Waves
Surface Waves
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Fig. 16.05
P or Primary Waves:
• Compression/Expansion (“Sound”)
• Solid and Liquid, through the Earth (Body Wave)
S or Secondary Waves:
• Transverse
• Solid Only, through the Earth (Body Wave)
Surface (Love/Raleigh) Waves:
• Transverse/Circular (“Ocean”)
• Solid Only, Near land surface
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Velocity ~ Density?
Density ~ Depth?
Seismogram – record of ground
movement produced by a
seismograph
P-wave velocity will always be
higher than S-wave velocity,
no matter what the waves
travel through.
P-waves arrive at the station
first, followed by S-waves and
later by surface waves.
Because S-waves travel more slowly than P-waves, the farther the waves have traveled, the
farther behind the S-waves will be and the longer the time gap until they arrive.
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http://www.gly.uga.edu/railsback/GeologicalDiagrams1.html
P
or Primary
Waves:
Fastest
– Arrives
Two
cars leave
Rock Hill,
Galleria
Mall,First
I-77 at the same time to Charleston.
S or Secondary Waves: Middle
Surface
(Love/Raleigh)
Waves:
Slowest
– Arrives
Last(P Wave)
One drives
60 mph (S Wave)
and
one drives
80 mph
Time:
7:14 = 14
after
7 oclock
At Columbia,
60minutes
miles, 60
minutes
& 45 minutes
Difference
Arrive Times
Arrival timeindifference:
15between
minutes the P and S Waves
7:17.4
– 7:14.2,240
ignore
the3.75
7:00hours and 3 hours
At
Charleston,
miles,
Minutes
17.4 minutes
– 14.2 minutes
= ? 3.2
Arrival
time difference:
0.75 hours
or 45 minutes
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Each line is representative of a
particular type of seismic wave.
Which is the fastest wave?
Which is the next fastest wave?
L Wave
Why curved lines?
Why straight line?
S Wave
P Wave
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Earthquake in Pacific Northwest
Waves arrive in Denver
distance: 2000 km
Waves arrive in St. John’s
distance: 5300 km
Waves arrive in Lima
distance: 9000 km
Fig. 16.10
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Fig. 16.09
The difference between the arrival times for P-waves and S-waves can be used to determine
the distance to the earthquake’s epicenter
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P-Wave:
8:07.4
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S-Wave:
8:11.5
11.5 – 7.4 = 4.1 minutes
L Wave
4.1 minutes
S Wave
P Wave
~ 2,600 km
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Right Lateral vs. Left-Lateral
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Strike-Slip Fault
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ACTIVITIES:
HANDOUT: By Table
Spring and Compression/Lateral Waves
As available (one spring, short exercise)
Demonstration of method
10 meter = ~33 feet (32.81 feet)
2 Way = 2 Round Trips = 40 m
4 Way = 4 round Trips =80 m
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ACTIVITIES:
MANUAL: By Table
16.2: A (discuss only), B, C, D
16.3: All
16.4: A, C
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