Earthquakes
Earth Science - Middle School
Earthquakes
Multimedia Lesson
Plate Tectonics
Multimedia Lesson
Earth's Interior
Presentation
Heat Transfer and Convection Currents
Presentation
How an Earthquake Occurs
Presentation
Types of Stress in Crustal Rock
Presentation
Faults in the Earth's Crust
Presentation
How Earth's Surface Changes
Presentation
Seismic Waves
Presentation
Measuring Earthquakes
Presentation
Earthquake Safety
Presentation
Earthquake Simulator
Virtual Lab
Earth's Interior
Interactive
Earthquake and Seismogram
Interactive
Earthquakes
Study Guide
Earthquakes
Quiz
Earthquakes
Quiz
Earthquakes
Flash Cards
Earthquakes
Flash Cards
Earthquakes
Worksheet
Earthquakes
Worksheet
Earthquakes
Game
Earthquakes
Game
Earthquakes
Vocabulary List
Earthquakes
Vocabulary List
Science: Earth Science
Flip Chart
Earthquakes
Flip Chart
Earthquakes
Flip Chart
How an Earthquake Occurs
Flip Chart
Types of Stress in Crustal Rock
Flip Chart
Faults in the Earth’s Crust
Flip Chart
How Earth’s Surface Changes
Flip Chart
Seismic Waves
Flip Chart
Measuring Earthquakes
Flip Chart
The Richter Scale
Flip Chart
Earthquake Destruction
Flip Chart
Earthquake Safety
Flip Chart
Minerals
Flip Chart
Rocks
Flip Chart
Fossils
Flip Chart
Geologic Time Scale
Flip Chart
Plate Tectonics
Flip Chart
Earthquakes
Flip Chart
Weathering of Rocks & Soil Formation
Flip Chart
Earth’s Atmosphere
Flip Chart
Understanding Weather
Flip Chart
Our Solar System
Flip Chart
Science: Earth Science
Flip Chart
Study Guide Earthquakes
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EARTHQUAKES The theory of plate tectonics describes the movement of the plates of the lithosphere relative to each other. This movement creates forces that push and pull on the crust. Crustal rock can absorb and store energy, but only so much. There is a point at which the stress is more than the rock can hold and the rock breaks. When the rock breaks, the stored energy is released and this energy travels through the Earth. This sudden release of energy created when rocks break is called an earthquake. The point in the crust where the rock first breaks to create an earthquake is called the focus of the earthquake. The point directly above the focus on the surface of the Earth is called the epicenter. Following a true earthquake event there can be smaller earthquakes that occur near the original earthquake focus. These aftershocks are smaller in magnitude than the original earthquake. Lesson Checkpoint: What do we call the point in the Earth’s crust where the rock first breaks to create an earthquake? Types of Stress Acting on Rocks Stresses are created whenever one mass of rock moves relative to another. When two tectonic plates are pushing toward each other, compressional stress deforms and breaks the rocks. Folded mountains are a typical result of compressional stress. When two plates are moving away from each other, tensional stress is created which creates faults that allow blocks of crust to move down relative to one another. Plates can also slide past one another. This creates transform faults, which also creates stress on both plates. Lesson Checkpoint: Name and describe one type of stress on the rock and plates of the Earth. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Faults When rocks break and there is movement on a plane (that is, a surface), the surface formed by the plane is called a fault. When a fault forms, one block is above the fault and the other is below the fault. The block above the fault is called the hanging wall. The block below the fault is called the footwall. • When the hanging wall moves up relative to the footwall, a reverse fault is formed. • A reverse fault in which the fault is at a very shallow angle is called a thrust fault. • When the hanging wall moves down relative to the footwall, a normal fault is formed. • When two blocks slide past one another, a transform fault is formed. Lesson Checkpoint: What are the two parts of a fault? Types of Seismic Waves When rock breaks, the energy that was stored in the rock is released in a single, massive event. The energy travels through the Earth, rolling and shaking the crust. This event is known as an earthquake. The energy is released in the form of energy waves. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
There are three different types of energy waves (seismic waves) released by an earthquake. • P-waves or primary waves are the first energy waves released. They are the fastest of the seismic waves and can travel through solids, liquids, and gases. Because they are the fastest seismic waves, they are the first waves to be measured by a seismograph. P-waves are pulse waves that move rock back and forth, first compressing then stretching the rock. • P-waves • S-waves or secondary waves are the second type of waves created by an earthquake. S-waves are slower than P-waves and therefore arrive at a seismograph after the P-waves. S-waves are also called shear waves because they travel in an S pattern through the rock, creating shear stresses. • • • S-waves can travel through solids, but they cannot travel through liquids. The disappearance of S-waves at the outer crust/mantle boundary is what indicates the outer core is liquid. • The slowest and most destructive seismic waves created by an earthquake are called surface waves. Surface waves travel along the surface of the Earth’s crust in a circular motion. They are the most destructive of the seismic waves because they shake the surface of the Earth up and down. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Surface waves Lesson Checkpoint: Which type of seismic wave is the most destructive? How Are Earthquakes Measured? Earthquakes are measured by machines called seismographs. The different seismic waves are measured and recorded on a paper or drum (or as a computerized image) called a seismogram. The first up tick on a seismogram records the arrival of the P-waves. The next significant up tick is the arrival of the S-wave. The most significant and dramatic waves recorded are the surface waves. The seismogram also records the times at which the different waves arrive. Knowing the differences in the times of arrival of the different waves can be used to calculate the distance from the seismograph to the location of the earthquake’s epicenter. Readings from three different seismographs are needed to determine the epicenter of an earthquake. The information from the seismogram can determine the distance from the seismograph to the epicenter, but it can’t determine the direction. The intersection of three circles, representing three distances from the epicenter to the seismograph stations, can determine the location of the epicenter. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
The strength of an earthquake is recorded on a scale from 1 to 10, where 1 is the mildest and 10 the strongest and most destructive. This measurement scale was developed in 1935 by Charles Richter and Beno Gutenberg and is called the Richter Scale. It is a base 10 logarithmic scale. Consequently, a magnitude 5 earthquake is over 900 times more powerful than a magnitude 3 earthquake. Lesson Checkpoint: Readings from how many different seismographs are needed to find the epicenter of an earthquake? Earthquake Damage and Safety Damage to buildings, structures, and infrastructure is caused by the rolling surface waves. The damage seen here in the famous magnitude 8 San Francisco earthquake of 1906 was only partly from the earthquake itself. The complete destruction of the city was due more to the fact that the earthquake broke the water pipes so firemen could not fight the fires. The city burned to the ground. Modern engineering techniques are attempting to limit such earthquake damage. Surface waves cause the surface to literally rise and fall. As the ground moves, buildings twist and deform and fall over: the earthquake shakes the “feet” out from under them. Construction engineers are using advanced techniques to minimize, and hopefully eliminate, such structural damage caused by earthquakes. This not only reduces damage and the costs related to that damage, but more importantly it reduces the chances of injury and death. For example, engineers have constructed buildings that are attached to the ground with shock absorbers that are made out of rubber and steel. The shock absorbers take the energy of the earthquake and limit the amount that actually shakes the building. People who live in earthquake-prone areas need to learn to take precautions and make safe decisions during an earthquake. Those who are outside must stay outside, away from buildings and structures. Those who are inside are advised to stand in doorways or crouch under a table in the middle of a room (that is, away from the walls) to avoid injury from falling ceiling and wall material. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Table Of Contents: Earthquakes
1. How an Earthquake Occurs
2.1. Rock Experiences Stress
The Earth's tectonic plates are in motion. This movement creates forces called stress that push and pull the rock within the Earth's crust.
2.2. Rock Releases Energy
Stress can cause rock to break and release stored energy in the form of seismic waves. These waves travel through the Earth and an earthquake occurs.
2.3. Earthquake Focus and Epicenter
The point where the rock first breaks is called the focus of an earthquake. The point directly above the focus on the Earth's surface is the epicenter.
2.4. Earthquake Aftershocks
After an earthquake event, smaller earthquakes called aftershocks often occur near the focus of the original earthquake.
2. Types of Stress in Crustal Rock
3.1. Three Types of Stress
There are three types of stress that occur in the crustal rock—tension, compression and shearing. Over long periods of geologic time, stress causes the earth's surface to slowly change.
3.2. Tension
When two tectonic plates are moving away from each other, tension pulls and stretches rock.
3.3. Compression
When two tectonic plates are pushing toward each other, compression squeezes rock, causing it to fold or break.
3.4. Shearing
Shearing stress occurs when two blocks of rock are pushing in opposite directions. This sliding motion can cause rock to change shape or break.
3. Faults in the Earth's Crust
4.1. What is a Fault?
A fault is a break in the Earth's surface that is created when crustal rock breaks and the rock surfaces move past each other. Most faults occur along tectonic plate boundaries.
4.2. Hanging Wall and Footwall
When a fault forms, the block of rock that is above the fault line is called the hanging wall and the block below is called the footwall.
4.3. Normal Fault
A normal fault is formed when tension causes the blocks of earth to pull apart and the hanging wall moves down relative to the footwall.
4.4. Reverse Fault
A reverse fault is formed when compression pushes the blocks of earth against each other and the hanging wall moves up relative to the footwall.
4.5. Strike-Slip Fault
A strike-slip fault is formed when blocks of rock slide past each other and experience shearing stress. This type of fault is usually found at tectonic plate transform boundaries.
4. Pause and Interact
5.1. Review
Use the whiteboard tools to complete the activity.
5. How Earth's Surface Changes
6.1. Folding Rock
When two plates are pushing against each other, rock can fold due to compression. An anticline is an upward fold that forms arches. A syncline is a downward fold that forms valleys.
6.2. Stretching Rock
Divergent plates often cause the formation of two normal faults in a block of rock. The downward movement of the hanging walls causes the rock in-between to move upward. This stretching of the crust forms fault-block mountains.
6.3. Uplifting Rock
Large areas of flat land and rock called plateaus are uplifted by plate movements that create stress in the crust.
6. Seismic Waves
7.1. What is a Seismic Wave?
When crustal rock breaks, stored energy is released in a single, massive event called an earthquake. The vibrations that travel through the Earth are called seismic waves.
7.2. Types of Seismic Waves
A seismograph detects and measures three types of seismic waves. P waves and S waves travel from the focus of an earthquake through the Earth's interior. When the energy reaches the surface of the crust, surface waves are created.
7.3. P Waves
P waves, or primary seismic waves, are the fastest moving waves. They travel through solids, liquids and gases. The pulsing of P waves causes rock to move back and forth, first compressing and then stretching the rock.
7.4. S Waves
S waves, or secondary waves, are slower than P waves and can travel through solids, but not liquids. S waves move in an S pattern, creating shear stresses that cause the crust to move from side to side and up and down.
7.5. Surface Waves
The slowest and most destructive seismic waves are called surface waves. One type of surface wave travels in a circular motion, moving the surface up and down. Another type causes back and forth motion.
7. Measuring Earthquakes
8.1. Seismographs
Seismographs are machines that detect and measure seismic waves caused by earthquakes. A seismogram is the tracing of an earthquake's motion. The arrival time and magnitude of each type of seismic wave is recorded in a seismogram.
8.2. Distance to Epicenter
Seismologists use the P and S wave arrival times to calculate the distance between the location of the seismograph and an earthquake's epicenter. The more time that passes between the arrival of the waves, the greater the distance from the epicenter.
8.3. Epicenter Location
Readings from three different seismograms are needed to determine the epicenter of an earthquake. Circles are drawn indicating epicenter distances. The intersection of these circles is the location of the epicenter.
8.4. Richter Scale
The strength of an earthquake is recorded on a scale of 1 through 10, where 1 is the weakest and 10 is the strongest. This is called the Richter scale and was developed in 1935.
8.5. Richter Scale is Logarithmic
The Richter scale is logarithmic, not linear. The amplitude of waves on a seismogram is 100 times greater in a magnitude 7 earthquake as compared to a magnitude 5 earthquake. The amount of energy released between each level on the scale increases at an even greater rate.
8.6. Mercalli Scale
The Mercalli scale is used to measure an earthquake's intensity as it relates to the amount of damage the earthquake causes. Locations closer to the epicenter typically have a higher score on the Mercalli scale.
8. Pause and Interact
9.1. Review
Use the whiteboard tools to complete the activity.
9.2. Earthquake and Seismogram
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.
9. Earthquake Safety
10.1. Potential Earthquake Destruction
The length and intensity of an earthquake determine the amount of destruction it can cause. Landslides, tsunamis and shifting ground caused by strong earthquakes can result in significant damage to buildings, highways and city infrastructures.
10.2. Risk of Earthquake
Scientists predict the risk of future earthquakes by studying the locations of faults and analyzing the information from past earthquakes. Some places such as the western coast of the United States are at higher risk for earthquake activity than other locations.
10.3. Safer Buildings in Earthquake Zones
Buildings in earthquake-prone locations are constructed to better withstand the motion caused by seismic waves. Steel cross braces, flexible pipes, and shock absorbers are some of the technologies being used.
10.4. Individual Safety During an Earthquake
If an earthquake occurs and you are inside a building, crouch under a table or doorway away from outer walls, and cover your head and neck. If you are outside, go to an open area that is away from power lines and buildings, and lie face down.
10. Vocabulary Review
11.1. Earthquakes Vocabulary Matching
The length and intensity of an earthquake determine the amount of destruction it can cause. Landslides, tsunamis and shifting ground caused by strong earthquakes can result in significant damage to buildings, highways and city infrastructures.
11. Virtual Investigation
12.1. Earthquake Simulator
In this virtual investigation you will study simulated earthquakes from different locations in the world. After an earthquake occurs, you will gather information from three seismograms. Using the data provided, you will determine the epicenter and the magnitude of each earthquake.
12. Assessment
13.1. Earthquakes
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