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Earthquakes
Liz LaRosa http://www.middleschoolscience.com 2009
What is an earthquake?
TB pg. 211
• Vibrations in the ground that result from
movement along breaks in the earth’s
lithosphere.
• Can also be caused by volcanic or magmatic
activity
Three Types of Faults, TB pg.213
ReverseOccurs on a convergent boundary
Strike-SlipOccurs on a transform boundary
NormalOccurs on a divergent boundary
What causes earthquakes?
TB pg. 213
• Tectonic plates move past each other causing
stress. Stress causes the rock to deform
– Plastic deformation – does not cause earthquakes
– Elastic deformation – rock stretches then reaches
a breaking point, releasing energy.
Elastic Rebound – deformed rock goes
back to its original shape
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
TB pg. 214
Focus – point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above focus
How Seismographs or Seismometers
Work, TB pg. 217
-measures ground motion and can be used to
determine the distance seismic waves travel
the pendulum remains Video link:
http://www.cleanvideosearch.com/media/action/yt/watch?v=Gbd1F
cuLJLQground
moves beneath it
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Typical Seismograma graphical illustration
of EQ waves
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Primary Waves (P Waves)
TB pg. 215
• A type of seismic wave that compresses
and expands the ground
• The first wave to arrive at an
earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Secondary Waves (S Waves)
TB pg. 215
• A type of seismic wave that moves the
ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Comparing Seismic Waves
Surface Waves, TB pg. 215
• Move along the Earth’s surface
• Produces motion in the upper crust
– Motion can be up and down or rolling motion
– Travel more slowly than S and P waves
• More destructive
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-use 3 seismic stations
• Triangulation locates the earthquakes
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
How are Earthquakes Measured?
3 Scales are used:
Richter Scale-magnitude-from 0-no
limit, amount of ground motion
Moment magnitude-magnitude—
total amount of energy in EQ
Modified Mercalli Scale-intensitymeasures damage from shaking, IXII
Richter Scale
How are Earthquakes Measured?
Mercalli Intensity Scale
Click Link for Interactive Demo
http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf
San Francisco Earthquake, 1989
History Channel Video
http://www.history.com/topics/1989-san-francisco-earthquake
http://www.civildefence.govt.nz/assets/Uploads/images/raildamage.jpg
Earthquake Waves & Earth’s Interior
Earthquake Risk-TB pg. 220
Tsunamis
Brain POP-click on pic
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Formation of a tsunami
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Tsunami Warning System
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt