Download Earthquakes

Earthquakes
Chap. 19
Forces within the Earth
Kobe, Japan
Seismic Waves
Measuring and Locating Earthquakes
Earthquakes and Society
Forces within the Earth – 19.1
Objectives
• define stress and
strain as they apply
to rocks
• distinguish among
the three types of
faults
• Contrast three types
of seismic waves
Fault scarp
I. Physics and Forces
I. Physics and Forces
A. Stress – the force per unit area
I. Physics and Forces
A. Stress – the force per unit area
1. Compression – decreases the volume.
I. Physics and Forces
A. Stress – the force per unit area
1. Compression – decreases the volume.
2. Tension – pulls apart.
I. Physics and Forces
A. Stress – the force per unit area
1. Compression – decreases the volume.
2. Tension – pulls apart.
3. Shear – twists.
I. Physics and Forces
B. Strain – deformation due to stress
I. Physics and Forces
B. Strain – deformation due to stress
1. Compression Strain
I. Physics and Forces
B. Strain – deformation due to stress
1. Compression Strain
2. Tensional Strain
I. Physics and Forces
B. Strain – deformation due to stress
1. Compression Strain
2. Tensional Strain
3. Shear Strain
I. Physics and Forces
C. Stress/Strain Curve
I. Physics and Forces
D. Deformation – altering the shape
1. When too much stress
is applied, permanent
deformation occurs.
I. Physics and Forces
D. Deformation – altering the shape
1. When too much stress
is applied, permanent
deformation occurs.
2. Brittle objects cannot
withstand much stress
before they are
deformed.
II. Faults
Taiwan – fault line running through rice paddy
Fracture of system of fractures in the Earth’s
crust along which movement occurs.
II. Faults
A. Reverse Faults – faults caused by
horizontal compression
II. Faults
B. Normal Faults – faults caused by
horizontal tension
II. Faults
C. Strike Slip – faults caused by
horizontal shear
III. Earthquake Waves
A. Primary (P) waves
Compression (squeeze and
pull) waves. Compression
occurs in the same direction
as the wave travels.
Wave travels underground
(a body wave)
III. Earthquake Waves
B. Secondary (S) waves
Displaces particles at a right
angle to the wave motion.
Wave travels underground
(a body wave)
III. Earthquake Waves
C. Surface Wave
Particles move up/down and
side/side.
Wave travels at the surface.
IV. Earthquake ‘Anatomy’
A. Focus – point where an
earthquake originates (often
underground)
IV. Earthquake ‘Anatomy’
B. Epicenter – Point on Earth’s
surface directly above the focus.
The End
Seismic Waves – 19.2
Objectives
• Describe how a
seismometer works
• Explain how seismic
waves have been used
to determine the
structure and
composition of
Earth’s interior.
I. Seismometer
I. Seismometer
A. How does it work?
I. Seismometer
A. How does it work?
B. What is it used for?
I. Seismometer
A. How does it work?
B. What is it used for?
C. What does its output look like?
Can you label the waves?
Can you label the waves?
II.Travel-Time Curves
II.Travel-Time Curves
A. Scientists have measured the time
it takes seismic waves to travel.
II.Travel-Time Curves
A. Scientists have measured the time
it takes seismic waves to travel.
B. The graph.
III. The Earth’s Interior
III. The Earth’s Interior
A. The path of P-waves is linear
when traveling in the mantle.
III. The Earth’s Interior
A. The path of P-waves is linear
when traveling in the mantle.
B. The path of P-waves is bent when
it enters a different material.
III. The Earth’s Interior
A. The path of P-waves is linear
when traveling in the mantle.
B. The path of P-waves is bent when
it enters a different material.
C. S-waves cannot travel through
liquids.
The Earth’s Interior
What does the
s-wave shadow
indicate?
Why is there a
p-wave
shadow?
IV. The Earth’s Composition
IV. The Earth’s Composition
A. Lithosphere (crust and top layer of
mantle) is primarily igneous rocks
(granite, basalt, and peridotite).
IV. The Earth’s Composition
A. Lithosphere (crust and top layer of
mantle) is primarily igneous rocks
(granite, basalt, and peridotite).
B. The asthenosphere (partially melted
mantle) is peridotite.
IV. The Earth’s Composition
A. Lithosphere (crust and top layer of
mantle) is primarily igneous rocks
(granite, basalt, and peridotite).
B. The asthenosphere (partially melted
mantle) is peridotite.
C. The lower mantle is solid, made of
iron, silicon and magnesium oxides.
IV. The Earth’s Composition
A. Lithosphere (crust and top layer of
mantle) is primarily igneous rocks
(granite, basalt, and peridotite).
B. The asthenosphere (partially melted
mantle) is peridotite.
C. The lower mantle is solid, made of
iron, silicon and magnesium oxides.
D. The core is dense iron & nickel.
Challenge Problem
What is the Earth’s core volume? What is
the volume of Earth’s mantle?
• The earth’s core has a radius of 3450
km and a density of 12,500 kg/m3.
• The earth’s mantle has a radius of
6371 km and a density of 4200 kg/m3.
• Vsphere = 4/3 πr3
• 1 km = 1000 m
Measuring and Locating
Earthquakes
I. Magnitude and Intensity
I. Magnitude and Intensity
A. The
scale measures the
magnitude of an earthquake.
The energy of an earthquake’s waves
I. Magnitude and Intensity
A. The Richter scale measures the
magnitude of an earthquake.
B. The
scale also
measures an earthquake’s
magnitude.
Considers various seismic waves, size of
fault rupture, amount of movement, and
rocks’ stiffness
I. Magnitude and Intensity
A. The Richter scale measures the
magnitude of an earthquake.
B. The Moment Magnitude scale also
measures an earthquake’s
magnitude.
Considers various seismic waves, size of
fault rupture, amount of movement, and
rocks’ stiffness
I. Magnitude and Intensity
C. The
scale
measures the amount of damage.
I. Magnitude and Intensity
C. The modified Mercalli scale
measures the amount of damage.
II. Locations of earthquakes
II. Locations of earthquakes
A. The depth of focus determines the
damage of an earthquake.
The deeper the focus, the less damage
II. Locations of earthquakes
A. The depth of focus determines the
damage of an earthquake.
B. Earthquake distance is found using
the separation time for
and
____ __.
II. Locations of earthquakes
A. The depth of focus determines the
damage of an earthquake.
B. Earthquake distance is found using
the separation time for S waves and
P waves.
II. Locations of earthquakes
C. Data from at least three stations is
combined by a method called
triangulation.
II. Locations of earthquakes
C. Seismic Belts – Earthquakes are
plotted on a world map.
II. Locations of earthquakes
C. Seismic Belts – Earthquakes are
plotted on a world map.
The End
Earthquakes and
Society
I. Structural Damage
I. Structural Damage
A. Buildings made of ______ ,
_______ , or ______ experience
significant damage.
I. Structural Damage
A. Buildings made of ______ ,
_______ , or ______ experience
significant damage.
B. Buildings of a certain ______
experience significant damage.
I. Structural Damage
A. Buildings made of ______ ,
_______ , or ______ experience
significant damage.
B. Buildings of a certain ______
experience significant damage.
C. Earthquakes may cause ______
when soil is liquified.
Liquefaction
Process where soil strength is
reduced by earthquake shaking.
I. Structural Damage
D. Earthquakes may cause fault
scarps.
I. Structural Damage
D. Earthquakes may
cause fault scarps.
E. Offshore quakes
may cause
________, or large
waves.
F. High risk areas
II. Predicting Earthquakes
II. Predicting Earthquakes
A. Earthquake history – look at
past pattern. There is a seismic
gap on San Andreas Fault –
last major earthquake in 1906.
II. Predicting Earthquakes
A. Earthquake history – look at
past pattern. There is a seismic
gap on San Andreas Fault –
last major earthquake in 1906.
B. Measure accumulated strain.
The End