The Dynamic Earth

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The Dynamic Earth

• Part 1 Understanding Earthquakes

The most common cause of Earthquakes is FAULTING.
A Fault is a break in the earths crust.
Earthquakes occur when rocks slip past each other
along the fault line. This releases a tremendous
amount of energy.
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Studying Earthquakes

• Seismology the study of earthquakes.
• Seismograph an instrument used to detect and
  measure the shock (seismic) waves sent out by an
  earthquake.
• Seismogram a recording of the three types of
  seismic waves. (S, P and L)

Seismograph
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Types ofSeismic Waves

• Primary Waves (P Waves) Push / pull waves.
  (like a slinky) Can travel through solids
  liquids or gases. FASTEST WAVES!
• Secondary Waves (S Waves) Move at right angles
  to the direction of the wave (like a rope) Can
  travel through solids but not liquids or gases.
  Not as fast as P waves. (Arrive after the P
  Wave)
• Surface Waves (L Waves) Travel like waves in
  water. (up and down) Slowest wave but most
  destructive kind of wave.

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Seismograms
The Lag Time or S - P Interval is 4 seconds.
Magnitude - 3.1Distance -34 km(Only about 25
miles away from the epicenter.)
S Waves arrive after the P Wave. The lag time
between the arrival of the two waves is called
the S-P Interval
P Waves arrive at the recording station first.
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Earthquake Terms

• Focus the point beneath the earths surface
  where the earthquake occurs.
• Epicenter the point on the earths surface
  above the focus.

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Locating the Epicenter

• To locate the epicenter seismologists record
  the seismic waves from three different recording
  stations. They measure the time between the
  arrival of the P waves and the S waves. Circles
  are drawn based on this measurement. The
  epicenter is located where all three circles meet.

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Are We At Risk?
New Madrid Fault New Madrid, Missouri
You better believe it!
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New Madrid Earthquakes 1811 - 1812
- Changed the course of the Mississippi
River.- Created Reelfoot Lake in
Tennessee.- Rang church bells as far away
as Boston, Mass.
Several earthquakes occurred between December
1811 through February 1812. Estimated magnitudes
as high as 8.1
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United States Geological Survey
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QUAKES Activity

• Finding the Epicenter of an Earthquake

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When an earthquake occurs both P Waves and S
Waves are sent out in all directions. Since P
Waves travel faster than S Waves, the waves do
not reach a distant point at the same time. This
difference in time is known as the S/P Interval
or Lag Time.
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A P Wave travels through the earth at an average
of 6.1 kilometers per second (km / sec.)
How many kilometers would a P wave travel in 6
seconds?
6.1 km / sec.X 6 sec.____________
Multiply 6.1 times 6 seconds
36.6 km
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An S Wave travels through the earth at an average
of 4.1 km/sec.
How many kilometers would a S wave travel in 6
seconds?
4.1 km / sec.X 6 sec.__________
Multiply 4.1 km / sec. times 6 seconds
24.6 km
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If P Waves travel at an average of 6.1 km/sec.
then in 16 Seconds a P Wave will travel about 100
km.
If S Waves travel at an average of 4.1 km/sec.
then in 24 Seconds an S Wave will travel about
100 km.
6.1 km / sec. X 16 sec.__________
4.1 km / sec. X 24 sec.__________
97.6(100 Km)
98.4(100 km)
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Using this knowledge, we can see that the S-P
Interval or Lag Time is about 8 seconds if the
epicenter of an earthquake is 100 km away.
This means that the epicenter is 12.5 km away for
every single second of Lag Time
100 8 12.5
Remember! It takes data from three recording
stations to determine the epicenter of an
earthquake.
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An Earthquake has been detected Stand
by for data
You will now begin the QUAKES Practice Activity.
Wait for further instructions.