Download Earthquakes - Lindbergh Schools

Lesson 1:
What are earthquakes
and where do they
occur
Where do Earthquakes Occur?
• Earthquakes can occur near the Earth’s
surface or far below the surface.
• Most earthquakes occur at plate boundaries,
but some happen at faults located in the
middle of tectonic plates.
PLATE BOUNDARIES
Earthquake Locations Around the World
What Causes Earthquakes?
• Earthquakes are caused by movement along
faults.
• When stress is placed on rocks it deforms, or
changes.
• Rock is stretched and bent until it can no longer
take the stress.
• When enough stress builds up in the rock it, it
slips and energy is released.
• This energy is felt as an earthquake.
Earthquakes in St Louis??
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Do we live near a plate boundary?
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Do we live near a fault?
The New Madrid Fault
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If there is no plate boundary in the middle of the
United States, why did these earthquakes take
place?
Geologists are beginning to understand the
answer. The New Madrid Fault Zone is part of an
ancient plate boundary. In this area, the North
American Plate tried to form a divergent plate
boundary about 500 million years ago. The
splitting stopped before new plates could form.
The faults in the New Madrid Zone are remnants
of this old event. Earthquakes occur because the
North American Plate is still "settling down". The
faults in the New Madrid Zone do not reach the
Earth’s surface. They are buried beneath
thousands of feet of rock and sediment deposited
by the Mississippi River. Geologists have located
them by looking at the patterns of earthquakes in
the zone.
Several of the
largest earthquakes
ever recorded in the
United States
occurred in the
Midwest, far from
any plate boundary.
These earthquakes
took place in an area
called the New
Madrid Fault Zone,
named after the
town of New Madrid,
Missouri.
New Madrid Fault
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Over a three-month period in the
winter of 1811 to 1812, the New
Madrid Fault Zone was struck by
three huge earthquakes estimated to
be greater than magnitude 8.0
The New Madrid Fault is what causes
Alabama to experience earthquakes.
3 Types of Faults associated
with Earthquakes
PLATE MOTION
FAULT TYPE
Transform
Strike –Slip Fault
Convergent
Reverse Fault
Divergent
Normal Fault
Strike-Slip Fault occurs at a
Transform Boundary
Reverse Fault occurs at a
Convergent Boundary
Normal Faults occur at Divergent
Boundaries
How do Earthquake Waves Travel?


Energy released from moving
plates and faults travels through
the Earth as waves.
These waves are called seismic
waves.
Types of Seismic Waves
1. BODY WAVES: Seismic waves that travel
through the Earth.
2. SURFACE WAVES: Seismic waves that travel
along the surface.

WAVES TRAVEL:
1.At different speeds and
2 In different ways
Depending on what kind of material
they are moving through.
Seismic Wave Arrival
• First- P-waves
• Second- S-waves
• Third- Surface Waves
Quiz
•
•
•
•
•
•
1. Most Earthquakes occur along ________________.
2. The first seismic waves to arrive are______________.
3. The second seismic waves to arrive are _____________.
4. The last seismic waves to arrive are_______________.
5. Which seismic waves travel the fastest?___________
6. Which type of seismic wave can move through a solid,
liquid or a gas?________________
• 7. Which seismic wave cannot travel through material that
is completely liquid?______________
• 8. Which seismic waves are the slowest and the most
destructive?_______________
Seismograph
• A seismograph is an instrument used by scientists to measure
earthquakes.
• Seismologists who study earthquakes can determine when an
earthquake started by noting the arrival times of P-waves and Swaves.
• A seismograph records vibrations in the Earth and determines the
strength and location of an earthquake.
Ancient Chinese
Seismograph. The
ball would drop
from the dragon to
the frog. It told the
people which
direction the
earthquake come
from.
Seismograms
0
1
2
3
Time in Minutes
4
5
6
1. How many minutes did it take for the
P-Waves to arrive?
2. How many minutes did it take for the
S-waves to arrive?
3. How long did the surface waves last?
7
8
Epicenter
• The epicenter is the point on the
Earth’s surface directly above an
earthquake’s starting point.
Focus
• The focus is the point inside the
Earth where the earthquake begins.
• The epicenter is located directly
above the focus.
Volcanoes
form around
Vents
Lava
vents that
release magma
onto the Earth’s
surface.
Magma chamber
The Composition of Magma Determines
whether it is explosive or not!

High water content
• More likely to be

High
content
• More likely to be
• Why?

!!!
!!!
Silica has a thick, stiff consistency
• Flows slowly
• Tends to Harden in the volcano’s vent
Quiz Part 2
a. What physical event causes explosive
eruptions?
b. Would high water content increase
the likelihood of having an explosive
eruption?
c. Would high silica content increase
the likelihood of having an explosive
eruption?
What Erupts from a
Volcano?
Blocky lava
Lava can be
thick or thin.
Pahoehoe
Aa
Pillow lava
Types of Volcanoes
Shield volcano
Cinder cone volcano
Composite volcano
What causes volcanoes?
The Formation of Magma
• Mantle rock melts when the
temperature increases
or the pressure decreases.
What causes volcanoes?
Where Volcanoes Form
• Tectonic Plate Boundaries!!!
~75% world’s active volcanoes in Ring of Fire
What causes volcanoes?
What causes volcanoes?
Hot Spots
How do volcanologists predict
eruptions?

Measuring Small Quakes
• Before eruption, increase in number &
intensity
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Measuring Slope
• Bulges may form with magma (tiltmeter)

Measuring Volcanic Gases
• Outflow of volcanic gases


Sulfur dioxide, carbon dioxide
Measuring Temperature from Orbit
• Measure changes in temperature over
time
You should not be a
Volcanologist if….


Robert

McGimsey
USGS
A. Ozerov
You don’t like
hiking,
backpacking,
rock climbing,
etc.
You are not
interested in
experiencing
extreme
temperatures
and heights.
If you don’t
like to travel to
incredible
places and see
breathtaking
views of the
world.