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Where do most earthquakes occur?
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How do scientists learn about earthquakes?
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What is a volcano?
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Most earthquakes occur at boundaries of
tectonic plates.
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As plates move, their edges experience
stress.
Eventually, the stress becomes so great that it
breaks rock along the fault line.
Energy is released as seismic waves.
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The exact point inside Earth where an
earthquake originates is the focus.
The point on the surface directly above the
focus is the epicenter.
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Energy released by an earthquake is
measured as shock waves.
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Earthquakes generate three types of waves:
1.
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Longitudinal waves
moves fastest,
1st wave
Aka – Primary wave or P-wave
Compression wave
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Earthquakes generate three types of waves:
2. Transverse Wave
- slower than p-wave
- 2nd wave
- Aka – Secondary wave or S-wave
- Doesn’t travel thru liquids
- Transverse Wave
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Earthquakes generate three types of waves:
3. Surface Waves
- slowest wave
- 3rd wave
- Aka – seismic wave or l wave
- Moves only across Earth’s surface
- Most destructive
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Scientists use
seismographs
to determine
the epicenter
of an
earthquake.
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Geologists use earthquakes to study Earth’s
interior.
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Scientists use two scales to measure the
effects of earthquakes.
◦ Richter Scale – measures magnitude
◦ Mercalli Scale – measures intensity
◦ http://earthquake.usgs.gov/earthquakes/recenteqs
us/
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A volcano is any opening in the Earth’s crust
through which magma has reached the
Earth’s surface.
These openings are called vents.
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There are three main types of volcanoes:
1. Shield Volcanoes
2. Composite Volcanoes
3. Cone Volcanoes
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Volcano formed from a buildup of
magma/lava rich in iron and magnesium.
Shield volcanoes are some of the largest
volcanoes.
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Example: Mauna Loa in Hawaii 13,000 ft.
above sea level – 30,000 ft above sea floor
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Composite volcanoes are made from
alternating layers of ash, cinders, and lava.
Eruptions alternate between lava flows and
explosive activity.
Typically thousands of meters high and much
steeper than shield volcanoes.
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Example: Mt. Fuji, Mt. Hood, Mt. Rainier, Mt.
St. Helens
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Cinder cone volcanoes are the smallest and
most abundant volcanoes.
Usually active for a short period of time, then
dormant.
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Example: Paricutin, Mexico
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Most occur at convergent plate boundaries.
Around the Pacific Plate is known as Ring of
Fire.
75% of the active volcanoes in the world are
located around Ring of Fire.
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Underwater volcanoes occur at divergent
plate boundaries.
Example: Iceland (Mid Atlantic Ridge)
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Volcanoes also occur at hot spots.
Mantle plumes rise from deep within the
mantle and erupt at hot spots at the surface.
Example: Hawaii
http://volcanoes.usgs.gov/
http://www.history.com/shows/how-theearth-was-made/videos/the-krakatoavolcano#the-krakatoa-volcano
1.
2.
3.
4.
5.
Where do most earthquakes occur?
What is the difference between the epicenter
and focus of an earthquake?
Identify and describe the three type of
volcanoes.
Why do surface waves cause the most
damage in an earthquake?
Why might a sudden increase in the number
of earthquakes around a volcano indicate a
possible eruption?