E3.P3XB Unit
Plate Boundaries and Earthquakes
Types of Plate Boundaries
• Divergent
• Transform
• Convergent
Assignment
• Students are to draw a table
Boundaries
Convergent
Transform
Divergent
Corresponding
Faults
Surface
Features
Examples
What are Earthquakes?
Red Book Chapter 8 Section 1
Where Do Earthquakes Occur?
Where do Earthquakes Occur?
• Seismology- the study of Earthquakes
• According to the previous map, where do
Earthquakes occur?
• Answer: Earthquakes occur along fault lines due
to the continuous movement of the Earth’s
tectonic plates
The Largest Quakes occur due to the Pacific Plate!
• What phenomenon causes the Earth’s
Tectonic Plates to be in constant motion?
• Answer: Convection Currents of the Mantle
What Causes Earthquakes?
• The push, pull, and grinding of tectonics plates
against one another frequently causes
deformation of those plates
• Deformation- the change in the shape of the
rock as a response to tectonic motion
– There are two types of deformation
• Deformation
1. Plastic Rebound
•
•
The plate is deformed and takes on a new shape
– As if you were molding clay
Plastic Rebound does not cause Earthquakes
2. Elastic Rebound
•
•
The plate is deformed to a “breaking point” and snaps
back into its original shape or position with a great
release of energy
Elastic Rebound causes Earthquakes
Elastic Rebound has been known to leave
evidence such as displaced fence lines
All Are Earthquakes the Same?
Plate Motion/
Boundary
Fault Type
Surface
Features
Earthquake
Characteristics
Transform
Strike-Slip
“San Andres
Fault”
Moderate with
Shallow Waves
Convergent
Reverse/ Normal
Mountains and
Volcanoes
Strong with Deep
Waves
Divergent
None, there is no
contact
Mid-Ocean
Ridges
Weak with
Shallow Waves
How Do Earthquakes Travel?
• Seismic Waves- Waves of energy that travel
through the Earth
– Primary P Waves
– Secondary S Waves
• Body Waves
– Waves that travel in the interior of the Earth
– P and S waves are Body Waves
• Surface Waves
– Waves along that surface of the Earth that move
the ground just like the ocean waves
Assignment
1. Where do Earthquakes occur?
2. How do convection currents play a role in
causing Earthquakes?
3. What form of deformation causes
Earthquakes and offsets fence-lines?
4. Name the plate boundaries/motions from
weakest to strongest pertaining to
Earthquakes.
5. Why are Surface Waves more destructive to
buildings than P and S waves?
Measuring Earthquakes
Chapter 8 Section 2
Locating Earthquakes
• Seismographs- measure seismic waves
• Seismogram- unit of measurement as
recorded by a seismograph
What is the name of the Scientist
who studies Earthquakes?
• Seismologists study Earthquakes
• Earthquakes happen with Elastic Rebound
– The SNAP!
• The seismograph starts recording at the start
of the quake
– The more movement, the bigger the quake!
• By comparing the P and S Waves on the
machine, exact start time can be determined
Which Types of Wave Arrives First?
P-Waves arrive first. P for Primary! They are
faster because they travel through all types of
matter: Solid, Liquid, and Gas
• Focus- Earthquake’s starting point in the body
of the Earth
• Epicenter- location on the crust directly above
the focus
– Seismographs can also help to find the focus
• Scientists can see how far the Earthquake has
traveled in a certain amount of time to locate
the epicenter
Finding the Epicenter
1. Circles are
drawn
around each
effected
seismograph
station
2. Circles for
each station
have an
overlapping
point
3. When all
circles are
drawn, they all
intersect at
only one
point.
This spot is the
Epicenter!
Measurement Methods
• Richter Scale
– Invented by Charles Richter
– 1.0-10.0, bigger numbers for bigger damage
• Momentum Magnitude
– Records amount of energy released
– For every 1 pt on the Richter scale the energy
released is 31.7 times more
If an Earthquake is measured at a 3.5 Richter, what
is the Momentum?
3.5 x 31.7 = 110.95 units
Richter X 31.7 = Energy Units
Assignment
1. What is the difference between seismograph
and seismogram?
2. At least how many seismograph stations are
need to locate an epicenter?
3. What is the difference between the
Momentum Magnitude and the Richter
Scale?
4. If an Earthquake is 7.0 on the Richter Scale,
what is if on the Momentum Magnitude?
5. Which types of waves travel faster? Why?
Earthquakes and Society
Chapter 8 Section 3
Earthquake Hazard
• Earthquake Hazard- How prone an area is to
receive Earthquakes
– Determined by past and present seismic activity
Find where we live. Do we have a high or low hazard level?
Earthquake Forecasting
• What do you think it means to Earthquake
Forecast?
• Answer: The practice of predicting when and
where Earthquakes will occur!
• Seismologists have discovered patterns in
Earthquake activity that allows for predictions
• Fault zones are closely monitored for seismic
activity
Worldwide Earthquake Frequency Chart
Description
Richter Scale
Average Annual
Occurrence
Catastrophic
8.0 or Higher
1
Major
7.0-7.9
18
Strong
6.0-6.9
120
Moderate
5.0-5.9
800
Light
4.0-4.9
About 6,200
Minor
3.0-3.9
About 49,000
Very Minor
2.9 or Less
About 365,000
Which type of Quake is less prevalent? Most prevalent?
• The Gap Hypothesis – active faults with few
quakes are likely to have strong quakes
• Seismic Gaps – areas along a fault where few
quakes have occurred
• Seismic Gap Hypothesis helped seismologists
determine the time, place, and strength of the
1989 San Fran Quake
Earthquakes and Buildings
• When the ground shifts, the center of gravity
for a building shifts, and the building falls
• Earthquake resistance buildings:
– Mass Damper- weight on roof to stop movement
– Cross Braces- strengthen the floors
– Flexible Pipes- prevent breaks
– Active Tendon- base weight to stop movement
– Base Isolators- absorb seismic waves
Mass Dampers can be
metal weights or water filled tanks
Are You Prepared?
• Before Shaking Starts
– Put heavy objects on low shelves
• Less likely to hit anyone if they fall
– Designated meeting spots
• Communication lines will be out
– Stashes of flashlights, water, canned foods,
batteries, first aid, fire extinguisher
• When Shaking Starts
– Crouch/lay under sturdy table/desk
– Cover your head with your hands
– Remain in your vehicle
• After Shaking Stops
– Be wary of aftershocks and fire, glass, other hazards
– Meet family at designated area
Assignment
1. How is an area’s Earthquake Hazard determined?
2. Describe three ways to reinforce buildings.
3. Name four items to store in case of an
Earthquake.
4. Where is the safest place to be during an
Earthquake? A highway, times square, or the top
bowl at Ford Field. Why?
5. What is gap hypothesis and how does it forecast
Earthquakes?
6. Draw the 3-part Earthquake safety procedure.
The Impact of Earthquakes
Natural Disasters
• Earthquakes can cause many disasters such as:
– Tsunamis
– Landslides/Mudslides
– Avalanches
– Fires from gas leaks
– Floods
WEIRD!
• We know that many quakes occur on the West
Coast of the US, but did you know that the
Mid-West and East Coast can feel them, too?!
• In 1811, four HUGE quakes rocked Missouri,
causing the Mississippi to run backwards. The
waves traveled all the way to Boston and rang
the church bells!
Assignment
• What are the disasters causes by quakes?
• What is the safety procedure for both in cars
and in builds?
• Additional Worksheet