1. Mrs. Bartley’s Earthquakes
Chapter 4
Mrs. Bartley’s Earthquakes

2. Forces Inside Earth Objectives
Explain how earthquakes result from the buildup of stress in Earth’s crust
Contrast normal, reverse, and strike-slip faults

3. Causes of Earthquakes Passing the Elastic Limit Causes Faulting
Applied stresses can cause rocks to bend and stretch
Eventually rocks will break away from one another
Area in which the rocks break and move is called a fault
Vibrations produced is called an earthquake
Earth’s crust movement causes the stresses applied

4. Tension
The rocks on the crust are being stretched as two plates are moving apart
The middle becomes thinner until a normal fault occurs

5. Types of Faults p.120 Normal Fault Earth’s plates move apart
Movement of the plates causes tension
Rocks above the fault surface move downward in relation to the rocks below the fault surface

6. Rio Grande Rift Valley

7. Compression This stress force squeezes rock until it folds or breaks
This can create a reverse fault

8. Types of Faults p.121 Reverse Faults
Compression forces are applied because Earth’s plates are coming together
Causes rocks to bend and break
Rocks above the fault surface are forced up and over the rocks below the fault surface

9. Northern Rocky Mountains

10. Shearing This stress force pushes rock in two opposite directions
This can cause a strike-slip fault

11. Types of Faults p.121 Strike-slip Fault
Earth’s plates move sideways to one another
Creates a shear force
Rocks on either side of the fault surface are moving past each other without much upward or downward movement

12. San andreas fault

13. Earthquake Information
Objectives
Compare and contrast primary, secondary, and surface waves
Explain how an earthquake epicenter is located using seismic wave information
Describe how seismic wave studies indicate the structure of Earth’s interior

14. Types of Seismic Waves p.125
Earthquake focus
Focus – the point in Earth’s interior where the energy waves are produced
Seismic waves
Seismic wave - the energy waves that move outward from the earthquake focus and make the ground quake
Epicenter
The point on Earth’s surface directly above the earthquake focus

15. Types of Seismic Waves p.127
Primary waves
Energy waves that cause rocks to move back and forth in the same direction
Compression and stretching forces are created
Secondary waves
Energy waves that cause rocks to move at right angles to the wave

16. Types of Seismic Waves Energy waves that reach the Earth’s surface
Surface waves
Energy waves that reach the Earth’s surface
Energy waves that move rocks in an elliptical motion

17. Locating an Epicenter p.130
Seismic waves do not travel through earth’s surface at the same speed
Primary waves are the fastest
Surface waves are the slowest
Seismograph stations
Record the information from the earthquake by recording the different types of waves as they reach the station

18. Locating and Epicenter p.131
Epicenter Location
If information is received from the earthquake at three stations, then the epicenter can be located
A circle is drawn around each station on a map
The radius is equal to the distance from the station to the epicenter
The point in which all three circles intersect is the earthquake epicenter

19. Using Seismic Waves to Map Earth’s Interior
The speed of the waves changes as the depth changes
The speed changes in accordance to the density of the layers of Earth

20. Using Seismic Waves to Map Earth’s Interior
Structure of Earth
Inner core
Solid and very dense
Composed of mostly nickel and iron
Outer core
Liquid layer that surrounds the inner core
Composed of nickel and iron

21. Using Seismic Waves to Map Earth’s Interior
Mantle
Largest layer located above the inner core
Composed of silicon, oxygen, magnesium, and iron
Crust
Outermost layer
Solid and similar in composition to the mantle

22. Using Seismic Waves to Map Earth’s Interior
Moho Discontinuity
Boundary between the crust and the mantle
Seismic waves speed up as they reach this area
Seismic waves speed up as they reach more dense areas and slow down when the reach less dense areas
The more solid the layer the more dense

23. Using Seismic Waves to Map Earth’s Interior
Shadow zone
The area between degrees from the epicenter
Area in which seismic waves can’t be detected
What is the cause?
Secondary waves can’t be transmitted through liquid layers
Primary waves are slowed and deflected by the outer core and speed up again when the reach the solid inner core

24. Destruction by Earthquakes
Objectives
Define magnitude and Richter scale
List ways to make your classroom and home more earthquake safe

25. Measuring Earthquakes p. 135
Seismology
Seismologists - People who study earthquakes and seismic waves
Use instruments called seismographs
Record seismic waves
A drum with a sheet of paper vibrates and a stationary pen marks the vibrations on the paper
The height of the lines are used to measure the energy released from the earthquake called the magnitude

26. Measuring Earthquakes p.128
Earthquake Magnitude
Usually determines the strength of the break
Doesn’t determine the duration or the size
For each increase of 1is 10 times stronger
An earthquake of 4 is 10 times stronger than an earthquake of 3

27. Tsunamis p.137 Caused by the movement of the ocean floor
Causes a disruption in the water
Some are so wide that a large ship can travel over the wave without knowing
Recent earthquake in the Indian Ocean created a tsunamis that was 100 feet high and moving at 500 mph

28. Earthquake Safety Quake proofing your home
Place heavy objects near the floor
Fix gas appliances in place

29. 9.4 Living on a Fault Objectives
Recognize that most loss of life in an earthquake is caused by the destruction of human-made structures
Consider who should pay for making structures seismic safe

30. Who should pay for earthquake preparation?
Seismic safe structures
Structures that are resistant to the vibrations of Earth’s crust
Structures are made with moorings
Made of steel and are filled with alternating layers of rubber and steel
These structures absorb the energy produced from the earthquake