Download Earthquakes

What are earthquakes ?
Why do they occur?
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 are prime earthquake zones!
Earthquake Locations Around the World
What Causes Earthquakes?
Earthquakes are caused when
STRESS FORCES
build along faults and then are
suddenly released.
Tension forces / Tensile forces – either side of a fault is pulling
away from each other. This happens at divergent plate
boundaries.
Compression forces – either side of a fault is pressing against each
other. This happens at convergent plate boundaries.
Shearing forces – either side of a fault is sliding past each other.
This happens at transform boundaries.
STRESS CAUSES ROCK
TO CHANGE
Elastic Deformation
Rock folds and stretches until it deforms.
Rock is stretched and bent until it can no longer take the
stress.
EARTHQUAKE!
Elastic Rebound
No longer under stress, the rock returns to its original
shape
Elastic
ELASTIC REBOUND
Earthquakes in Pennsylvanai??
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Do we live near a plate boundary?
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Do we live near a fault?
USA Fault Systems
The New Madrid Fault
Under the Mississippi??!!
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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.
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 but are connected to other faults
closer to home!
East Coast Fault
and
Ramapo Fault Systems
The ancient Ramapo Fault System --- runs
through the eastern part of the PA.
Smaller modern faults in Pennsylvania and
along the Ramapo Fault Line are forming
and becoming active!
Earthquakes of Pennsylvania 1965-2012
Lesson 2
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
Chapter 8: Sections 1: Earthquakes and Faults:
Organizer
PLATE MOTION
FAULT TYPE
Transform
Strike –Slip Fault
Plates move past
each other
Fault blocks move past each other
Convergent Plates move together Reverse Fault
Fault blocks move together
Divergent
Plates move apart
Normal Fault
Fault blocks move apart
Lesson 3
How do Earthquake Waves Travel?
Energy released from
moving plates and faults
Travels through the Earth
in 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.
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WAVES TRAVEL:
1.At different speeds and
2 In different ways
Depending on what kind of material
they are moving through.
Body Waves
• There are two types of body waves:
– P-waves
– S-waves
P-waves
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P-waves are pressure waves.
P-waves travel through solid, liquids and gases.
P-waves are the fastest waves.
P-waves are the first waves to be detected and the first waves to
arrive.
P-waves are also called primary waves because they arrive first.
P-waves cause rock to squeeze and stretch. Imagine a slinky!
The area of the Earth that does not receive seismic energy is called
the shadow zone.
1.P-Waves
2. S-waves
S-waves are the second fastest waves.
 S-waves are also called secondary waves
because they arrive second.
 S-waves are slower than P-waves.
 S-waves move rock from side to side.
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S-waves can’t travel through parts of the
Earth that are completely liquid.
S-Waves
3. Surface Waves
• Surface waves move along the surface of
the Earth.
• Surface waves can move up, down and
around or side to side.
• Surface waves move the slowest and
cause the most destruction.
Surface Waves
Seismic Wave Arrival
• First- P-waves
• Second- S-waves
• Third- Surface Waves
Shadow Zone
The shadow zone results from S waves being stopped entirely by the liquid
core and P waves being bent (refracted) by the liquid core.
Moho Zone
The Moho is the boundary between the crust and the
mantle in the earth.
This is a depth where seismic waves usually increase
velocity, or speed and direction.
Quiz
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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?_______________
Lesson 4
Earthquake
Measurement
Seismograph
• A seismograph is an
instrument used by
scientists to measure
earthquakes – determines
the strength and location!
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.
Measuring Earthquakes
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There are two major ways
earthquakes are measured:
1. Richter Scale
2. Mercalli Scale
Richter Scale
Richter Scale
measures magnitude or energy
released by an earthquake
Less than 3.5-Generally not felt, but recorded.
3.5-5.4- Often felt, but rarely causes damage.
Under 6.0-At most slight damage to well-designed buildings.
Can cause major damage to poorly constructed buildings
6.1-6.9- Can be destructive in areas up to about 100
kilometers across where people live.
7.0-7.9- Major earthquake. Can cause serious damage over larger
areas.
8 or greater- Great earthquake. Can cause serious damage in areas
several hundred kilometers across.