Transcript 2nd revision Earthquakes

1. What are Earthquakes?
• The shaking or trembling caused by
the sudden release of energy
• Usually associated with faulting or
breaking of rocks
Where Do Earthquakes Occur and How Often?
~80% of all earthquakes occur in the circum-Pacific belt
•
most of these result from convergent margin activity
~15% occur in the Mediterranean-Asiatic belt
remaining 5% occur in the interiors of plates and on spreading
ridge centers
more than 150,000 quakes strong enough to be felt are recorded
each year
2. Earthquake Anatomy
o The actual place underground where the rocks break
producing vibrations is called the focus
o The place on the surface directly above the focus is
called the epicenter
3. What causes Earthquakes?
A. Movement along faults: occurs when the
energy exceeds the friction holding the sides of
the fault together and is suddenly released. This
is the Elastic Rebound Theory.
B. Movement of magma (volcanic)
C. Volcanic eruptions
What is the Elastic Rebound Theory?
•
Explains how energy is
stored in rocks
• Rocks bend until the
strength of the rock
is exceeded
• Rupture occurs and
the rocks quickly
rebound to an
undeformed shape
• Energy is released in
waves that radiate
outward from the
fault
4. What types of forces are created?
A. Extension Force:
 stretching or pulling force
 Makes a normal fault
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
4. What types of forces are created?
B. Compression Force:
 force pushing something together
 Makes a reverse fault
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
4. What types of forces are created?
C. Shear Force:
 a system of forces that operates
against a body from different sides
 Makes a strike-slip fault
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
Landscape Shifting, Wallace Creek
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Source: John S. Shelton
Geology, 10a–14
5. Seismic Waves
Originate at the focus and travel outward in
all directions
 Foreshocks: small earthquakes that come
before a major earthquake
 Aftershocks: Are adjustments in the crust
after an earthquake
6. How do we Measure Earthquakes?
A. Earthquake waves are recorded by a seismograph
and the recording of waves on paper is called
seismogram
6. How do we Measure Earthquakes?
 B. Richter Scale: Measures the amplitude of
earthquake waves on seismograms
 Scale from 1-10
 Each number is 10 times the amplitude of the
number below
7. Locating Earthquakes
• After an earthquake, the difference in arrival
times of seismic waves at a seismograph station
can be used to calculate the distance from the
seismograph to the epicenter.
7. Locating Earthquakes
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Geology, 10a–20
Map of
Epicenter,
KY, TN
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Geology, 10a–21
8. Earthquake Dangers
o A. Most injuries and deaths are caused by falling
objects and most property damage results from
fires that start
San Francisco, 1906
San Francisco, 1906
8. Earthquake Dangers
B. Tsunami: seismic sea wave sometimes
generated when an earthquake originates on the
ocean floor
Generation of a Tsunami
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Geology, 10a–26
Tsunami—December 2004
http://www.bedford.k12.ny.us:16080/flhs/science/images/tsunami2004/
Who Feels the Shaking?
• The shaking starts at the epicenter and
spreads in circles outward much like the
ripples of water dripping into a puddle.
NSF North Mississippi GK-8
8. Earthquake Dangers
C. Liquefaction: unconsolidated materials that are
water saturated may turn to a fluid causing some
underground objects such as storage tanks to float to
the surface
Ground fissures caused by liquefaction near the
mouth of the Pajaro River in California during the
1989 Loma Prieta earthquake. When the surface
of the ground oscillates, wet, sandy, and muddy
soils can flow like a liquid. This is liquefaction. You
can liquefy wet sand at the beach by pumping it up
and down with your feet. Photo courtesy of the
Loma Prieta Collection, Earthquake Engineering
Research Center, UC Berkeley.
Liquefaction
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Geology, 10a–30
Liquefaction
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Source: Steve McCutcheon/Alaska Pictorial Services
Geology, 10a–31
Elevated
Freeway
Collapse
in Kobe
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Source: Hosaka Naoto/Gamma Liaison
Geology, 10a–32
8. Earthquake Dangers
D. Landslides
Earthquake Safety




Protect yourself from falling objects (GET UNDER SOMETHING)
or stand in a hallway or doorway (watch out for a swinging door)
Do not try to go outside during the earthquake
After the earthquake and before the aftershocks, go outside
Do not return to the building until it has been inspected