Earthquakes
Liz LaRosa http://www.middleschoolscience.com 2009
for my 5th grade science class 2009
What is an earthquake?
• The slipping and breaking of rock material
along a fault.
• Faults are “cracks” in the crust near plate
boundaries that are under stress.
• Stress is caused by the heat within the earth
trying to escape and the movement of the
plates.
Three Types of Faults
Strike-Slip - shearing
Thrust - Compression
Normal – pulling away
What causes earthquakes?
• 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 – kind of
bounces back like a rubberband.
Elastic Rebound – deformed rock goes
back to its original shape
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Focus –
point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above focus
Seismic
Waves in
the Earth
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Primary Waves (P Waves)
• 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)
• A type of seismic wave that moves the
ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Typical Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Comparing Seismic Waves
Surface Waves
• Move along the Earth’s surface
• Produces motion in the upper crust
– Motion can be up and down
– Motion can be around
– Motion can be back and forth
• 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
• The further away an earthquake is, the
greater the time between the arrival of
the P waves and the S waves
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
Earthquake Waves & Earth’s Interior
How Seismographs Work
the pendulum remains
fixed as the ground
moves beneath it
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
How are Earthquakes Measured?
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
Tsunamis
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