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EARTHQUAKES
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2007 Japan quake
EARTHQUAKES
What are earthquakes?
They are a shaking of the ground.
1906 San Francisco quake,evacuation
by sea
The Study of Earthquakes
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What is seismology?
It is the study of earthquakes
Where do most earthquakes occur?
Near the edges of tectonic plates.
What are tectonic plates?
Giant pieces of Earth’s thin, outermost layer
Tectonic plates move in different directions and at different speeds
Two plates can push toward or pull away from each other. They can
slip slowly past each other.
What happens as a result of these movements of plates?
A fault
A fault is a break in the Earth’s crust along which blocks of the crust
slide relative to one another.
Earthquakes occur along faults because of this sliding
What Causes Earthquakes?
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As tectonic plates push, pull or slip past each other, stress increases along faults near the
plate’s edges.
This causes the rock to deform
What is deformation?
It is the change in the shape of rock in response to stress.
How many ways does a rock deform?
Two
In a plastic manner or in an elastic manner
Plastic deformation does not lead to earthquakes
What type of deformation does lead to earthquakes?
Elastic deformation
What is elastic rebound?
The sudden return of elastically deformed rock to its original shape
What is released during elastic rebound?
Energy
What does some of this energy travel as?
Seismic Waves, which causes earthquakes
Plate Motion and Fault Types
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Plate Motion
Transform
convergent
Divergent
Fault type
strike-slip fault
reverse fault
normal fault
Faults at Tectonic Plate Boundaries
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What is transform motion?
It occurs where two plates slip past each other
Transform motion creates strike-slip faults. Blocks of crust slide
horizontally past each other
What is convergent motion?
It is where two plates push together
Convergent motion creates reverse faults. Blocks of crust that
are pushed together slide along reverse faults
What is divergent motion?
It occurs where two plates pull away from each other
Divergent motion creates normal faults. Blocks of crust that are
pulled away from each other slide along normal faults
How Do Earthquake Waves
Travel?
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What are waves of energy that travel through the Earth called?
Seismic Waves
Seismic waves that travel through the Earth’s interior are called what?
Body waves
What are the two types of body waves?
P waves and S waves
What are seismic waves that travel along earth’s surface called?
Surface waves
Waves that travel through solids liquids and gases are called P waves.
P waves are the fastest waves, so they travel ahead of other seismic waves.
What are P waves also called?
Primary waves because they are the first to be detected in an earthquake
When are S waves created?
When rock deformed from side to side springs back to its original position
What is another name for S waves?
Shear waves
They are the second fastest of the seismic waves
They stretch the rock sideways
They arrive after P waves and are also called secondary waves
Surface waves move along the earth’s surface and produce motion mostly in the upper few kilometers of
Earth’s crust
Earthquake Measurement
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How do scientists know when and where earthquakes begin?
They depend on seismographs
What is a seismograph?
An instrument located at or near the surface of the Earth that record seismic
waves
When the waves reach a seismograph it creates a seismogram
What is a seismogram?
The tracing of earthquake motion
Seismologists use seismograms to calculate when an earthquake began
How do seismologists find the start time of an earthquake?
They find it by comparing seismograms and noting the differences in arrival
times of P waves and S waves.
What is an epicenter?
It is the point on Earth’s surface directly above an earthquakes starting point
What is a focus?
The point inside the Earth where an earthquake begins
Seismograph
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Seismogram being created
Measuring Earthquake Strength
and Intensity
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The Richter Scale was used to measure strength of earthquakes
throughout the 20th century
Who designed the Richter Scale?
Charles Richter in the 1930s
What is the measure of the strength of an earthquake called?
Magnitude
What is intensity?
The measure of the degree of an earthquake felt by people and
the amount of damage caused
What is used to measure intensity of an earthquake?
The Modified Mercalli Intensity Scale
Earthquakes and
Society
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Why is it important for people in earthquake zones to
be prepared before an earthquake strikes?
Seismologists are not always able to predict the exact
time and place when an earthquake will occur.
What is an earthquake hazard?
It is a measurement of how likely an area is to have
damaging earthquakes in the future.
What is retrofitting?
It is the process of making older structures more
earthquake resistant.