Download Chapter 19 Earth quakes

Chapter 19 Earth quakes
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I. Forces within Earth
A. Stress and Strain
1. Most earthquakes occur when rocks
fracture, or break, deep within Earth.
2. Fractures form when stress, forces per
unit area acting on a material exceeds the
strength of the rocks involved.
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3. Compression is stress that decreases the
volume of a material.
4. Tension is stress that pulls a material
apart.
5. Shear is stress that causes a material to
twist.
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Compression Strain
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Tensional strain
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Shear Strain
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B. Faults
1. A fracture along which movement
occurs is called a fault.
2. There are three basic types of faults,
reverse, normal and strike-slip fault.
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3. Reverse faults are
fractures that form as a
result of horizontal
compression.
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4. Normal faults are
fractures caused by
horizontal tension.
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Strike-slip faults are
fractures caused by
horizontal shear.
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Top-reverse/ Center –normal/ Bottom- Strike Slip
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C. Earthquake waves
1. Primary waves or P-waves squeeze and
pull rocks in the same direction along
which the waves are traveling.
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2. Secondary waves, or S-waves cause rocks
to move at right angles in relation to the
direction of the waves.
3. Surface waves are a third type of seismic
wave that move in two directions as they
pass through rock.
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4. The point where an earthquake originates
is the focus of the earthquake.
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II. Seismic Waves and Earth’s
Interior
A. Seismometers and Seismograms
1. Seismometer is an instrument that
detect and record vibrations.
2. Seismogram- the record produced by a
seismometer.
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19.3 Measuring and Locating
Earthquakes
A. Earthquake Magnitude and Intensity
1. The amount of energy released during and
earthquake is measured by its magnitude.
2. An earthquake’s rating on the Richter scale is
based on the size of the largest seismic waves
generated by the quake.
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3. The moment magnitude scale takes into account
the size of the fault rupture, the amount of
movement along the fault, and the rock’s
stiffness.
4. Modified Mercalli scale rates the types of damage
and other effects of an earthquake as noted by
observes during and after its occurrence.
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B. Locating an earthquake
1. The exact location of an earthquake’s
epicenter and the time of the quake’s
occurrence are initially unknown.
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2. All epicenter locations, as well as times of
occurrence, can be determined using
seismograms.
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C. Seismic Belts
1. Seismologists have collected and
plotted the locations of numerous
earthquake epicenters.
2. Almost 80% of all earthquakes occur in
the Circum-Pacific Belt.
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19. 4 Earthquakes and Society
A. Some earthquake hazards
1. The damage produced by an
earthquake is directly related to the
strength or quality of the structures
involved.
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2. Most severe damage occurs to
unreinforced buildings made of stone,
concrete, or other brittle material.
3. Wooden structures are strong.
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4. Usually the supporting walls of the ground
floor fail and cause the upper falls to fall
and collapse.
5. In addition to their effects on structures
made by humans, earthquakes can destroy
Earth itself-landslides.
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6. Fault Scarps are fault movement associated
with earthquakes can produce areas of great
vertical offset where the fault intersects the
ground surface.
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7. A tsunami is a large ocean wave generated
by vertical motions of the seafloor during an
earthquake.
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Tsunami before and after
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7. The probability of future quakes is much
greater in the belts than elsewhere around
the globe.
8. Seismic gaps are sections of active faults
that haven’t experienced significant
earthquakes for a long period of time.
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THE END
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