Earthquakes

```Earthquakes
Today’s Journey
• 0507.7.1 Create a model to illustrate geologic events
responsible for changes in the earth’s crust.
• 0507.7.2 Prepare a chart to compare how volcanoes,
earthquakes, faulting, and plate movements affect the
earth’s surface features.
• State Performance Indicators
• SPI 0507.7.1
Describe internal forces such as
volcanoes, earthquakes, faulting, and plate movements that
are responsible for the earth’s major geological features
such as mountains, valleys, etc.
What is an earthquake?
• Used to describe both sudden slip on a fault,
and the resulting ground shaking and radiated
seismic energy caused by the slip (Transform
Boundaries)
• Caused by volcanic or magmatic activity,
• Caused by other sudden stress changes in the
earth.
Three Types of Faults
Strike-Slip
Thrust
Normal
What causes earthquakes?
• Tectonic plates move past each other causing
stress-built up energy on a fault. Stress causes
the rock to deform.
– The amount of energy released depends on how
much rock breaks and how far the blocks of rock
move.
Focus – point inside the Earth where an earthquake begins; most of these
are less than 45 mi below the surface.
Epicenter – point on Earth’s surface above focus
Where do you think would the intensity be strongest?
• The hardest shaking is going to be at the
epicenter of an earthquake because the
seismic waves at the focus of an earthquake
are the strongest and the epicenter is directly
above it.
– These seismic waves spread out from the focus.
As they do, their energy grows weaker.
How Seismographs Work
the pendulum remains
fixed as the ground
moves beneath it
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Typical Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
There are two types of Seismic Waves
• Body Waves-move through the “body” of the
Earth or the inside.
– They can pass through rock and liquid.
• Surface waves-move along Earth’s surface.
Primary Waves (P Waves)
• A type of seismic body wave that
compresses and expands the ground
• The first wave to arrive at an
earthquake
• When they reach the surface, they
cause rock to move back and forth.
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Secondary Waves (S Waves)
• A type of seismic body wave that moves
the ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Comparing Seismic Waves
Make a quick venn diagram to compare the two types of body waves that
occur due to an earthquake.
Surface Waves
• Move along the Earth’s surface
• Known as L waves
• Produces motion in the upper crust
– Motion can be up and down
– Motion can be around
– Motion can be back and forth
• Travel more slowly than S and P waves
• More destructive because they make the ground swell
and roll like ocean waves.
• Do not travel too far from the epicenter.
How do scientists calculate how far a location is
from the epicenter of an earthquake?
• Scientists calculate the difference
between arrival times of the P waves
and S waves
• The further away an earthquake is, the
greater the time between the arrival of
the P waves and the S waves
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
How are Earthquakes Measured?
Richter Scale
6: Very Strong
7: Severe
2-4:
8: Violent
Moderate- Weak
9: Extreme
5: Strong
How are Earthquakes Measured?
Mercalli Intensity Scale
http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf
Earthquake Waves & Earth’s Interior
Bill Nye
Earthquake
Clip
Seismic
Waves in
the Earth
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Tsunamis
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Formation of a tsunami
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Today’s Journey
• 0507.7.1 Create a model to illustrate geologic events
responsible for changes in the earth’s crust.
• 0507.7.2 Prepare a chart to compare how volcanoes,
earthquakes, faulting, and plate movements affect the
earth’s surface features.
• State Performance Indicators
• SPI 0507.7.1
Describe internal forces such as
volcanoes, earthquakes, faulting, and plate movements that
are responsible for the earth’s major geological features
such as mountains, valleys, etc.
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