Transcript Earthquakes - Science with Mrs. Lambert

Earthquakes
Chapter 19
Earthquakes
Natural vibrations of the ground caused
by strain along faults in Earth’s crust
Faults: the fracture or system of
fractures along which movement occurs
San Andreas Fault: famous U.S. fault
line (California)
– N.American plate sliding past Pacific plate
– http://pubs.usgs.gov/gip/earthq3/where.html
Types of Faults
Reverse
– From compression (convergent
boundaries)
Normal
– From tension (divergent boundaries)
Strike-slip
– From shear (transform boundaries)
Types of Faults
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Reverse Fault
Strike-slip Fault
Normal Fault
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Elastic Rebound Theory
When two plate slide past
each other, they
eventually ‘snag’ on each
other and begin to pull.
The ground can only
‘stretch’ so far and when
that snag fails, the ground
snaps back into place
(like a rubber band)
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Seismic Waves
All Earthquakes release seismic waves
3 types of seismic waves:
– P-Waves - primary, travel through all
material, fastest, back & forth motion
– S-Waves - secondary, travel through solids
only, 2nd fastest, move up & down
– L-Waves - surface, travel along surface,
slowest, move back and forth AND up and
down
Seismic Waves
P-waves:
http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif
S-waves:
http://www.geo.mtu.edu/UPSeis/images/S-wave_animation.gif
L-waves:
http://www.geo.mtu.edu/UPSeis/images/Love_animation.gif
Seismic Waves
Used to determine the Earth’s layers
These waves move through Earth & will
only pass through certain materials tells scientists what’s inside the Earth
Locating Earthquakes
Seismometer: machine that
picks up Earthquake waves
Because seismic waves travel
at different speeds, they arrive
at a seismometer at different
times
Difference between P and S waves
can tell how far away an earthquake
occurred
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Locating Earthquakes
Information from 3 seismometers is needed
to plot where an earthquake occurred
(triangulation)
Focus: point inside the Earth where the EQ
begins/starts
Epicenter: point on the surface of Earth
directly above the focus - reported in the
news as the location of the EQ
Locating Earthquakes
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Measuring Earthquakes
Richter Scale: measures Earthquake
magnitude (energy)
– Scale from 1-10
– Strongest: 9.5 in Chile (1950)
Mercalli Scale: measures Earthquake
intensity (damage)
– Scale from I - XII
– Used by insurance companies
Where do Earthquakes
Occur?
Pacific Ring of Fire - 80%
Eurasian Belt - 15%
Mid-Ocean Ridges - 5%
United States
– Most occur on West coast
– Strongest Quake: St.Louis (1813)
Earthquake Hazards
Buildings fall, glass breaks, roads crack,
bridges fall
Slope failure (landslides)
Tsunami
Safest place to be:
– Away from buildings
– In a doorway
Earthquake Prediction
Can we predict Earthquakes?
– NO
– Best scientists can do is to say they think
one may occur in the next 100 years
California: Parkfield experiences a
magnitude 6 earthquake every 20-30
years - last one was Sept.2004
– http://earthquake.usgs.gov/research/parkfield/