Download UNIT 3: DYNAMIC EARTH Chapter 9: Volcanoes

Chapter 10: Earthquakes
10.1: How and Where Earthquakes Occur
10.2: Locating and Measuring Earthquakes
10.3: Earthquake Hazards
10.4: Studying Earth’s Interior
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10.1: How and Where Earthquakes Occur
A.
Causes of
Earthquakes
1. Earthquake-The
shaking of Earth's crust
caused by a release of
energy.
2. The cause of most
major earthquakes is
strain that builds up
along faults.
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10.1: How and Where Earthquakes Occur
3. Fault-A break in the
lithosphere along
which plate
movement occurs.
4. Focus-The point at
which first movement
occurs during an
earthquake.
5. Epicenter-The point
on the earth's surface
directly above the
focus.
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10.1: How and Where Earthquakes Occur
B.
Body Waves
1.
2.
The energy from an
earthquake is released
in the form of waves.
Body Waves- Waves
that travel from the
focus to through the
body of the earth.
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10.1: How and Where Earthquakes Occur
3.
P waves-Compression
waves that squeeze
and stretch rock
material. They can
travel through any
material (water,
magma, rock and air).
4.
S waves- Shear waves
that cause material to
move at right angles to
the direction of wave
travel. They can travel
through solids but not
liquids or gases.
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10.1: How and Where Earthquakes Occur
C. Surface Waves
1. Earthquake waves that travel on
the surface.
2. Appear when P and S waves
reach the surface.
3. Cause the most damage. Why?
Because they are on the surface
4. Two Types: Love and Rayleigh.
Love waves move side to side.
Rayleigh move in elliptical
patterns.
•
•
•
Animations of earthquake
waves
Examine P and S waves
Savage Earth: Restless
Planet
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10.2: Locating & Measuring Earthquakes
A.
Seismograph
1. Detects and records waves produced by earthquakes.
2. Seismogram-A record sheet placed on a drum. The
drum turns slowly and any movement is recorded on
the paper. See page 217.
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10.2: Locating & Measuring Earthquakes
B. Interpreting a Seismogram
1. P waves arrive first, then S waves.
2. The farther the station is from the earthquake, the larger
the separation between P & S waves lines. Why?
More time to get ahead. It is like a race between two
people at different speeds.
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10.2: Locating & Measuring Earthquakes
C. Locating the Epicenter
1.
We can triangulate
the epicenter by
using three different
seismic stations.
See page 219.
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10.2: Locating & Measuring Earthquakes
D. Measuring an
Earthquakes Magnitude
1.
Magnitude-A
measure of the
amount of energy
released in an
earthquake.
2.
The Richter Scale
was developed in
1935. It measures
the amount of energy
released by an
earthquake.
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10.2: Locating & Measuring Earthquakes
3. An increase of one whole
number is equal to a 31fold increase in energy.
Ex. Mag. 6 earthquake is
31 times more powerful
than a Mag. 5
earthquake.
•
Build Your Own
Seismograph
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10.3: Earthquake Hazards
A.
Damage from Earthquakes
1.
Damage is not only caused by the shaking from the
earthquake, but also by foundation failure, fire and
tsunamis.
2.
Liquefaction-Occurs when loose soil temporarily takes on
some of the properties of a liquid. This causes buildings
and roads to collapse.
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10.3: Earthquake Hazards
3. Aftershocks-Series of small
earthquakes that follow the
initial quake.
4. Fire can cause substantial
damage. It is usually
triggered by ruptured gas
lines.
5. Tsunamis-A huge ocean wave
triggered by an earthquake.
Can travel long distances at
speeds up to 750 kph.
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10.3: Earthquake Hazards
B.
Preventing Earthquake
Damage
1.
Earthquake prone cities
have special building
codes to help prevent
building collapse.
2.
Monitoring equipment
helps to continue
learning what structures
hold up the best during
an earthquake.
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10.3: Earthquake Hazards
C. Earthquake Risk
1.
Areas near plate
boundaries are not the
only areas at risk.
2.
New Madrid, MO is
located near several
faults buried under large
amounts of sediments.
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10.3: Earthquake Hazards
D. Predicting Earthquakes
1.
Seismic Gaps- Areas where stress may be
building up along a fault.
2.
Scientists can predict at risk areas, but not
specific locations or times.
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10.4: Studying Earth’s Interior
A.
The Shadow Zone
1.
2.
Changes in the speed
and direction of P and
S waves indicate
changes in the
composition and state
of the earth's interior.
A shadow zone is
created by these
changes. Remember
that S waves cannot
travel through liquids.
See page 228.
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10.4: Studying Earth’s Interior
B. The Moho
1.
Boundary between the
crust and the mantle.
2.
Where the dense rock of
the mantle meets the
less dense rock of the
crust.
3.
Located about 32 km
under continents and 510 km under the oceans.
Why?
The crust is thinner in the ocean.
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10.4: Studying Earth’s Interior
Transition Zone
C.
1.
2.
Region in the middle of the mantle where the
densities of the upper and lower mantle vary.
This change is due to changes in pressure as depth
increases.
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