Earthquakes!

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Earthquakes!

• Adapted from www.middleschoolscience.com

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What is an earthquake?

• Used to describe both sudden slip on a fault, and
  the resulting ground shaking and radiated seismic
  energy caused by the slip
• Caused by volcanic or magma activity,
• Caused by other sudden stress changes in the
  earth.

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Three Types of Faults
Strike-Slip
Thrust
Normal
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What causes earthquakes?

• Tectonic plates move past each other causing
  stress. Stress causes the rock to deform, break,
  and/or move

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Elastic Rebound deformed rock goes back to its
original shape
http//www.uwgb.edu/dutchs/EarthSC-102VisualsIndex
.HTM
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Focus point inside the Earth where an
earthquake beginsEpicenter point on Earths
surface above focus
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How Seismographs Work
Its a weighted pen writing on a rolling drum of
paper.
the pendulum remains fixed as the ground moves
beneath it
this mass, like the pen, has inertia and so
resists motion.
Normally everything would move, but.
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Typical Seismogram
http//isu.indstate.edu/jspeer/EarthSky/EarthCh11
.ppt
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Primary Waves (P Waves)

• PUSH-PULL PATTERN!
• A type of seismic wave that pushes pulls the
  ground
• The FIRST wave to arrive from an
  earthquaketravels the fastest!
• Travels Parallel to the direction the wave travels

http//daphne.meccahosting.com/a0000e89/insideear
th2.htm
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Secondary Waves (S Waves)

• A type of seismic wave that moves the ground up
  and down or side-to-side (perpendicular) to the
  direction the wave travels
• Slower!
• More destructive
• to buildings

http//daphne.meccahosting.com/a0000e89/insideear
th2.htm
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(No Transcript)
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Comparing Seismic Waves
P S Wave song http//www.youtube.com/watch?v
w3NLexYxR7g
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Surface Waves

• Move along the Earths surface
• ROLL OUT! Motion can be up and down, around
  back forth
• Travel more slowly than S and P waves
• Last to arrive
• Most destructive to structures

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How do scientists calculate how far a location is
from the epicenter of an earthquake?

• Scientists calculate the difference between
  arrival times of the P waves and S waves
• The further away an earthquake is, the greater
  the time difference between the arrivals of the P
  waves and the S waves

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Locating Earthquakes
Question Where could the EQ be?

1. Find the difference in the arrival times, or lag
   time ( t ), of the P S waves.

3. Use the distance from the EQ as the radius (r)
for this circle.
r
?Difference in arrival times?
P-wave
S-wave
2. Find the distance to the EQ using the lag time
and this Time/Distance graph.
Time ( t)
Answer Anywhere along the blue line. (not much
help)
Distance (km)
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Locating Earthquakes
Question Where could the EQ be, now?
Lets get someone else that has readings for
this EQ to help out (Same procedure)
?Difference in arrival time?
\?Arrival diff.?\
Answer Where the green and blue circles
cross. (Better, but still a 50-50 change of going
to the right place to find the EQ.)
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Locating Earthquakes
So, no more guessing Question where is the
actual EQ ?
If you get 3 people working on this puzzle, now
you can triangulate.
?Difference in arrival time?
\?Arrival diff.?\
\?Arrival time diff. ?\
Answer Where all 3 circles intersect
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How are Earthquakes Measured? Richter
Scale-measures energy
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How are Earthquakes Measured? Mercalli
Scale-measures damage
Click Link for Interactive Demo
http//elearning.niu.edu/simulations/images/S_port
folio/Mercalli/Mercalli_Scale.swf
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Earthquake Waves Earths Interior
See how seismic waves move through the Earths
layers here (Shadow zone) http//www.classzone.co
m/books/earth_science/terc/content/visualizations/
es1009/es1009page01.cfm
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Seismic Waves in the Earth
http//www.uwgb.edu/dutchs/EarthSC-102VisualsIndex
.HTM
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Tsunamis
http//www.uwgb.edu/dutchs/EarthSC-102VisualsIndex
.HTM
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Formation of a tsunami
http//isu.indstate.edu/jspeer/EarthSky/EarthCh11
.ppt
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Tsunami Warning System
http//isu.indstate.edu/jspeer/EarthSky/EarthCh11
.ppt