Download Earthquakes

Earthquakes
Lesson 4.8
What is an earthquake?
• Tectonic plates move past each other causing
stress. Stress causes the rock to deform
– When the stress is too great, the rock will rupture
and cause and earthquake
– Released as seismic wave
Focus – point inside the Earth along a fault
where an earthquake begins
Epicenter – point on Earth’s surface above focus
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.
• Rock returns to nearly the same shape after the stress
is removed- Elastic Rebound
Elastic Rebound – deformed rock goes back to
its original shape
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Where do earthquakes happen?
• At divergent boundaries, tension stress causes
normal faults to form. Earthquakes tend to be
shallow because the crust is thin.
Copyright © Houghton Mifflin Harcourt Publishing Company
Where do earthquakes happen?
• At convergent boundaries, rock is squeezed,
causing reverse faults to form. Earthquakes can
be very strong and deep.
Copyright © Houghton Mifflin Harcourt Publishing Company
Where do earthquakes happen?
• At transform boundaries, shear stress pushes
tectonic plates in opposite directions. Earthquakes
tend to be relatively shallow.
Copyright © Houghton Mifflin Harcourt Publishing Company
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
Comparing Seismic Waves
Earthquake Waves & Earth’s Interior
How are Earthquakes Measured?
Richter Scale
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 Seismographs Work
the pendulum remains
fixed as the ground
moves beneath it
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Typical Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
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
Tsunamis
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Tsunami
• An earthquake under the water cause vertical
movement of the sea floor
– Moves an enormous amount of water
• May cause a tsunami
• Tsunami- a series of extremely long waves that
travel quickly across the ocean
– Travel outwards in all direction from point where
earthquake occurred
Tsunami Approach
• As the wave approaches the shoreline, it
increases in size
– Can be taller than 30 M
– Destroy anything in their path
• Can cause:
– Floods
– Polluted water supplies
– Large amounts of debris
Formation of a tsunami
Tsunami Animation
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Tsunami Warning System
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt