CK-12 Earth Science for Middle School FlexBook® 2.0 Answer Key
Chapter 6: Geological Activity and Earthquakes
6.1 Geological Stresses
Review
Questions
1. What type of stress would you find at a transform fault? 2. What type of stress would you find at a subduction zone? 3. Under what conditions will a rock fracture?
Answers
1. Shear 2. Compression 3. There is so much stress that the rock can’t deform elastically or plastically.
6.2 Principle of Horizontality
Review
Questions
1. Why are sediments laid down horizontally? 2. Why are sediments laid down from oldest to youngest? 3. Why are sedimentary rocks so good for studying the geology of a region?
Answers
1. Gravity brings them into horizontal position. 2. For B to be above A, A had to have been there first. 3. They reveal the history of the area; e.g. if there was deformation or not.
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Questions
1. How is rock laid down? 2. What is the law of superposition? 3. Why is the law of superposition important?
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4. Where is the oldest rock found? 5. Where is the youngest rock found? 6. Why do we know that the fault is younger than the three rock layers? 7. Is the intrusion the youngest rock in the section? How do you know?
Answers
1. Horizontally 2. The law that says that the oldest rock is on the bottom and the rocks get younger going upward if the section is not deformed. 3. The law can be used to figure out the history of an area. 4. The oldest rock is found at the bottom. 5. The youngest rock is at the top. 6. The rock layers had to be there for the fault to cut across them. 7. The intrusion is not the youngest because it does not cut across the rock layers that are above it. They are younger.
6.3 Folds
Review
Questions
1. Draw a picture to show how compressive stresses lead to folds. Can these stresses create anticlines and synclines? 2. Do you think that anticlines and synclines are ordinarily found separately or next to each other? 3. Describe domes and basins. Where are the youngest rocks in each?
Answers
1. Yes, compressive stresses can lead to anticlines and synclines. 2. They are often found adjacent to each other like in the image at the top of the concept. 3. A dome is a circular anticline. The youngest rocks are on the outsides. A basin is a circular syncline. The youngest rocks are in the center.
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Questions
1. What is a geologic fold and what causes one to form? 2. What types of forces create a set of folds?
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3. What is a monocline? Where are the older rocks found? 4. What is an anticline? Where are the older rocks found? 5. What is a syncline? Where are the older rocks found?
Answers
1. Flat rocks become deformed due to stress and pressure. 2. Compressive 3. A dip or drop in a area of flat or sloping rock. Older rocks are at the bottom. 4. A fold that arches away from Earth. The oldest rocks are at the center. 5. A fold that arches into Earth. The oldest rocks are at the outside.
6.4 Faults
Review
Questions
1. Compare and contrast normal and reverse faults. 2. Imagine you’re looking at a cliff with layers of rock. What features would you see to indicate a fault? 3. What is a strike-slip fault? 4. What type of plate boundary can be a strike-slip fault or fault zone?
Answers
1. In a normal fault, the hanging wall goes down relative to the footwall, but it is the opposite in a reverse fault. 2. A fault is indicated because rock layers are offset by the fault. So if you follow a particular rock layer across the hill and then it disappears and reappears above or below its original level, it was displaced by a fault. 3. A strike slip fault has a vertical fault plane with lateral movement. 4. A transform plate boundary is marked by a strike-slip fault, like the San Andreas Fault.
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Questions
1. In a normal fault, which is the hanging wall and which is the footwall? 2. What is the stress in a normal fault? 3. What is the stress in a reverse fault? 4. How does the hanging wall move relative to the footwall in a reverse fall? 5. Describe a strike-slip fault.
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Answers
1. The footwall is the one a person would be standing on with the hanging wall above. 2. Tension 3. Compression 4. The hanging wall moves up relative to the footwall. 5. A strike-slip fault has shearing so that one block moves horizontally in one direction and the other block moves in the opposite direction.
6.5 Mountain Building
Review
Questions
1. Describe how plates create mountain ranges like the Himalayas. 2. Diagram how pulling apart continental crust could create mountains and basins. What are the mountains and basins called? 3. Why don’t strike slip faults create mountains?
Answers
1. The Indian Plate is colliding with the Eurasian plate. 2. Pulling apart of crust creates blocks of crust separated by normal faults. The blocks fall to different levels. The ones that are high create ranges and the ones that are low create basins. 3. There is no vertical movement in a strike-slip fault so no mountain ranges.
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Questions
1. What created the landscape we see today on Earth? 2. What can cause mountains to form? 3. What are the Rocky Mountains made of? 4. How were the Rockies formed? 5. Why did the Rockies form so far inland from the plate margin?
Answers
1. Granite moved by plate tectonics create the landscape we see today. 2. Mountains are usually formed by plate convergence.
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3. Granite 4. The Rocky Mountains were formed when a subducting plate pushed back upwards on a center part of the overlapping plate, pushing it upwards. 5. The Rockies are far from the plate margin because they are not formed by a plate convergence.
6.6 Earthquakes
Review
Questions
1. Describe elastic rebound theory. 2. Where is an earthquake’s focus? Where is its epicenter? 3. Why do shallow earthquakes cause the most damage?
Answers
1. Stresses build up until they can’t build up any more and the rock breaks. It rebounds into its earlier shape, but it may have changed position. 2. The focus is where the earthquake happens in the Earth. The epicenter is just above the focus. 3. Shallow earthquakes cause the most damage because their focus is near the surface where people and buildings are.
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Questions
1. What is it called when you feel the ground move? 2. What does the Earth’s interior resemble? What is the outside layer called? 3. What is Earth’s outer layer made of? What are they called? 4. How fast does this outer layer move usually? 5. What is a fault? How big are they? 6. What happens when too much pressure builds up at a fault?
Answers
1. An earthquake. 2. The Earth’s interior has layers like a cake. The outer layer is called the crust. 3. The crust is made of multiple pieces called plates. 4. 1 cm per year. 5. A fault is the line where two plates meet and run the entirety of the plate.
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6. When two plates get stuck together at a fault, the pressure builds up until the rocks break, causing an earthquake.
6.7 Earthquake Zones
Review
Questions
1. Why are most earthquakes at plate boundaries? 2. What two types of plate motions cause earthquakes around the Pacific Ring of Fire? 3. What type of plate motions cause the Mediterranean-Asiatic quakes?
Answers
1. Plates don’t move easily. 2. Convergent and transform 3. Convergent
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Questions
1. What was the magnitude of the Chilean earthquake? 2. What two plates are converging near Chile that caused the earthquake? 3. What is the Ring of Fire? What occurs along this Fing of Fire? 4. What was the strongest earthquake ever recorded? When did it occur? 5. Why are scientists urging Memphis to adopt building codes similar to Chile’s?
Answers
1. 8.8 2. The Nazca Plate is subducting beneath the South American Plate. 3. The Ring of Fire is a geologically active zone around the Pacific Ocean Basin, with many volcanoes and earthquakes. 4. 9.5; 1960 Chile 5. The New Madrid Fault produced a very large earthquake in the early 19th century. If one like that hit now there could be many fatalities since falling buildings are one of the things that kill people in a quake.
6.8 Earthquakes at Transform Plate Boundaries
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Review
Questions
1. Why are earthquakes at transform plate boundaries always shallow focus? 2. Why are there so many small faults in the San Francisco Bay Area? 3. Why do such large earthquakes take place along the San Andreas Fault?
Answers
1. There is no up and down motion; all movement is horizontal and is in the crust. 2. The movement must be taken up by all the faults together. 3. These are giant plates that are sliding past each other and it is not smooth.
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Questions
1. How far does the San Andreas Fault extend? 2. If you have one foot on each side of the fault, which plate is each foot on? What regions share each plate? 3. What type of fault is it? 4. What causes an earthquake? 5. What is a creepmeter? How much movement does the creepmeter in the video sense? 6. How many earthquakes occur at the San Andreas fault each year?
Answers
1. Mexico to Oregon 2. One foot is on the North American Plate, which includes New York and Iceland. One foot is on the Pacific Plate, which includes Hawaii and Japan. 3. Strike-slip 4. The plates get stuck; tension builds until the rock breaks and there is an earthquake. 5. A creep meter measures the slow movements along the fault; it senses 5 mm of movement. 6. More than 10,000 earthquakes strike the San Andreas Fault each year.
6.9 Earthquakes at Convergent Plate Boundaries
Review
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Questions
1. Why does a subducting plate produce so many earthquakes? 2. What depths of earthquakes does a subducting plate produce? 3. What caused the most destruction from the 2011 Japan earthquake? 4. In the cart above of depth vs distance of the earthquakes, what is being outlined by the dots?
Answers
1. The plate is plunging into the mantle. This is a difficult process and causes quakes. 2. Shallow, intermediate and deep quakes are produced by the subducting plate. 3. The most destruction was from the tsunami that followed the quake. 4. The dots outline a profile of the subducting plate.
6.10 Intraplate Earthquakes
Review
Questions
1. What caused the New Madrid earthquakes? 2. What causes intraplate earthquakes? 3. Why did an earthquake strike Virginia in 2011? Why did it strike at that location?
Answers
1. There is a zone of weakness in the region. Large slabs of crust moving over a spherical planet is not something that happens easily. 2. Plates move on the spherical planet, which is not smooth. Zones of weakness in the slab experience earthquakes. 3. Virginia was an active plate boundary when Pangaea came together. Those ancient faults get reactivated.
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Questions
1. How many active earthquake fault zones are there in the United States? 2. What is the second most active fault zone in the United States? 3. When did the New Madrid earthquake occur? 4. What was the magnitude of the New Madrid earthquake?
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5. How many aftershocks occurred? What was the highest magnitude of an aftershock? 6. How long is the New Madrid fault? 7. How many people would be affected by another quake? 8. Where is the Ramapo fault? 9. Why is quiet along an active fault considered a problem?
Answers
1. At least four 2. New Madrid 3. 1811 4. 7.5 5. 2,000 aftershocks; 8.0 magnitude (makes you wonder if that was the main quake and the 7.5 was a foreshock) 6. The New Madrid fault is 120 miles long and goes through five states. 7. Right now about 15 million people live in the New Madrid fault region. 8. The Ramapo runs through New York, New Jersey and Pennsylvania. 9. Stresses are building up so when a quake comes it will be bigger.
6.11 Seismic Waves
Review
Questions
1. Draw a set of waves and label the parts: crest, trough, amplitude, wavelength. 2. Compare and contrast P-waves and S-waves. 3. Describe the motions of surface waves.
Answers
1. See figure in text 2. Both are body waves so they travel through the planet. P-waves are faster so they arrive at a site first. They travel through all three of the states of matter. S-waves arrive second; they do not travel through gases or liquids. 3. Surface waves only travel around the surface of the planet. Love waves have a side-to-side motion and Rayleigh waves have a rolling motion. Both of these cause a lot of damage in an earthquake.
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Questions
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1. What are body waves? 2. Which waves move the fastest? 3. What are the S-waves? Describe them. 4. What happens to body waves as they move through the Earth? 5. What are the two types of surface waves? 6. Describe how surface waves travel.
Answers
1. Body waves travel through the interior of the Earth 2. P-waves move the fastest. 3. S-waves are shear waves that are slower than P-waves but faster than surface waves. 4. P- and S-wave velocities increase with depth in the planet; they slow as they near the surface on the other side. 5. Rayleigh and Love waves 6. Surface waves travel around the perimeter of the planet. They arrive after the body waves.
6.12 Tsunami
Review
Questions
1. Why is a wave that is so powerful and tall on land unnoticeable at sea? 2. What should you do if you are at the beach and the water suddenly is sucked offshore? 3. Describe tsunami as waves in the way they travel up a shoreline and may strike as crests or troughs.
Answers
1. The depth of the sea makes the wave unnoticeable. When the depth is reduced and the wave approaches the shore, then the wave becomes more powerful. 2. Run towards high ground.
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Questions
1. What does the word tsunami mean in Japanese? 2. Why has Japan had so many tsunamis? 3. What causes a tsunami? 4. How fast do the waves travel?
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5. What happens to the tsunami as it reaches the continental shelf? 6. How do tsunamis differ from regular waves? 7. What was the deadliest tsunami ever recorded? How many people died? 8. What does the Pacific Tsunami Warning Center do?
Answers
1. “Harbor wave” 2. Japan sits near the border of multiple intersecting fault lines, making underwater earthquakes and disturbances more common. 3. Tsunamis are caused by a sudden displacement of ocean water, such as in an earthquake. 4. 600 miles per hour. 5. The waves friction slows when it hits the shore line, and raises it’s height. 6. A tsunami wave doesn’t crest and break like a normal wave, instead it moves forward as a solid wall of water. 7. The Indian Ocean Tsunami in 2004, killing 220,000 people. 8. These centers monitor underwater earthquakes and alert vulnerable coastlines to incoming tsunamis.
6.13 21st Century Tsunami
Review
Questions
1. How can a wave that is so powerful and tall on land be unnoticeable at sea? 2. How does an earthquake generate a tsunami? 3. Why did the Boxing Day Tsunami cause so much damage all around the Indian Ocean basin? 4. Why do you think there was more damage from the tsunami in Japan than from the earthquake that caused it?
Answers
1. The waves have low amplitude, but long wavelengths; when they travel up the continental margin they are pushed upward and get much larger. 2. An earthquake releases lots of energy, which displaces the seawater and causes waves. 3. The earthquake that caused the tsunami was enormous and displaced a lot of water. Moreover, there was an open area all around the Indian Ocean basin for the waves travel through. 4. The quake was offshore, so it wasn’t that noticeable on land; the magnitude of the tsunami damage dwarfed whatever damage the quake had done.
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6.14 Measuring Earthquake Magnitude
Review
Questions
1. Define seismograph, seismogram, and seismometer. 2. What does a seismogram with P-waves but not S-waves mean and why? 3. How can you tell S-wave arrival from the end of the P-wave?
Answers
1. Seismograph: an older machine that detects seismic waves; seismogram: the paper record that the seismic waves are recorded on in a seismograph; seismometer: a modern machine that detects seismic waves 2. The earthquake was on the other side of the Earth because the S-waves didn’t go through the liquid outer core. 3. The P-waves taper off and the first S-waves display a sharp spike up and down.
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Questions
1. Why was the Alaska Earthquake on March 27, 1964 so large? How large was it? 2. Name the types of plate boundaries that experience earthquakes. 3. When geologists discovered new oceanic crust forming at divergent plate boundaries, what two explanations did they come up with? 4. What happens at a subduction zone? 5. What is the common cause of all 6 megathrust earthquakes that have been recorded since 1900? 6. Why is it impossible (at least at this time) to predict when an earthquake will take place?
Answers
1. This quake was a megathrust quake, meaning that the plate was thrust upwards when another plate subducting underneath it slipped, this was felt on 1.3 million square kilometers of Earth. 2. Convergent, divergent, and transform plate boundaries 3. At first, geologists thought that the Earth was growing, then later discovered that it was producing new crust in one area, while old crust subducted in another. 4. A subduction zone is the boundary at two converging plates where one plate is pushed under the other.
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5. The megathrust earthquakes occurred at a transform boundary where a subducting plate and the overlapping plate slipped. 6. There are many different forms of earthquakes and many complicated factors tie into their causes, detecting them is hard because any prior warning is subtle and occurs deep underground.
6.15 Locating Earthquake Epicenters
Review
Questions
1. How do you determine the distance from the seismograph to the earthquake epicenter? 2. How do you find the epicenter from three seismographs? 3. What role does the S-P interval play in locating an earthquake epicenter?
Answers
1. The distance to the epicenter is given by the P-S wave interval, the difference in the arrival time between the two types of body waves. 2. You calculate the distance for each seismograph so that you can draw a circle around that location that is that distance in radius; where the 3 circles intersect is the epicenter. 3. The S-P interval is crucial because it gives the distance from the seismograph to the epicenter.
6.16 Earthquake Magnitude Scales
Review
Questions
1. Under what circumstances might the Mercalli intensity scale be useful today? Why was it replaced by the Richter and then the moment magnitude scales? 2. Why do scientists prefer the moment magnitude scale to the Richter scale? 3. In 2011 there was a 5.8 magnitude quake that struck Virginia and a 9.0 quake that struck Japan. How might a 5.8 quake rate on the Mercalli scale in Virginia? How might a 5.8 magnitude quake rate on the Mercalli scale in Japan?
Answers
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1. Mercalli would be useful if there were no quantitative measures or if data from observations was somehow needed. This is qualitative, so it was replaced by other measures that are quantitative. 2. The moment magnitude is more accurate because it measures the total energy released rather than the just the size of the largest jolt, which is what the Richter scale measures. 3. Japan has lots of very large earthquakes so on a qualitative scale like Mercalli they might rate it lower than in Virginia where a small earthquake is a much bigger deal.
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Questions
1. What was the magnitude of the 2010 Haiti earthquake? 2. What does magnitude mean? 3. How much larger is each earthquake magnitude? 4. What is the difference between two magnitudes? 5. What was the largest earthquake ever measured?
Answers
1. 7.0 2. Magnitude is the amount of energy released by the quake. 3. Each whole number is 33x larger. 4. 33-times 5. 9.5 Chile in 1960
6.17 Predicting Earthquakes
Review
Questions
1. Why is it easier to predict where a quake will occur than when? 2. List some of the signs that may predict earthquakes. 3. Along which fault in the San Francisco Bay area is a large earthquake most likely to strike? 4. The map of earthquake probability from the San Francisco Bay Area was made in 2003. How has the probability likely changed since there's been no major earthquake there in more than a decade?
Answers
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1. The earthquake history of a region helps with predicting where quakes will take place. They may even give some sense of how often quakes occur in that region. But they give no information on exactly when a quake will occur. If a quake strikes a location about every 100 years and it’s been 100 years since the last quake, no one can tell exactly when the next quake will be. 2. Foreshocks, tilting, animal behavior, the difference in P- and S-wave arrival time lowers. 3. Rogers Creek Fault and Hayward Fault junction 4. No the probability is still the same.
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Questions
1. What happened on April 18, 1906? 2. How fast is movement usually along San Andreas Fault? What is the rate of movement during a major quake? 3. Why is it difficult to predict earthquakes? 4. What information would a really great earthquake prediction give? 5. What can provide a warning for earthquakes about 10% of the time? Why is this warning system not all that reliable? 6. Why is monitoring the Earth from space useful? What does it tell scientists?
Answers
1. A major earthquake in San Francisco along San Andreas Fault 2. A few millimeters a year; several thousand kilometers in an hour 3. It’s hard to find a feature that’s dependable and widespread. 4. A great prediction would tell the exact time, place and magnitude of an earthquake. 5. Foreshocks make a good warning system, but only about 10% of the time. It’s hard to tell if a large earthquake is a foreshock or if it’s the actual earthquake. 6. 6. From space, scientists can monitor stress in the crust. They can use real time GPS. The information helps them understand the approximate magnitude quake that can be expected.
6.18 Earthquake Damage
Review
Questions
1. What causes liquefaction? Why is it damaging?
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2. A 9.2 earthquake struck near Anchorage, Alaska in 1964, but few people died. If a similar quake struck today, how many fatalities would there be compared with the quake in 1964? Explain your reasoning. 3. Why do city planners look at Mercali maps rather than predictions of earthquake magnitude?
Answers
1. Liquefaction occurs when an earthquake causes sediments to saturate with water to become like quicksand. 2. In 1964 the population of Anchorage was much smaller than it is today and there was not nearly the amount of infrastructure. If a quake that size happened today there would be much more damage and many more fatalities. 3. The damage done by a quake in a local area depends on the local geology, such as the bedrock, not just the magnitude of the quake.
6.19 Earthquake Safe Structures
Review
Questions
1. What can be done to make a new building safer in an earthquake zone? 2. What can be done to retrofit an older building in an earthquake zone? 3. What can be done to reduce the damage from fire after an earthquake? 4. Should all buildings in all areas be built to the highest earthquake standards? What is a more cost-effective approach?
Answers
1. For large buildings, they must be anchored to the bedrock and able to sway but not too much. They can be put on rollers or on top of layers of steel and rubber. Smaller buildings can have some of those features, be made of wood. 2. Steel or wood is placed on the outside of the building to reinforce it. 3. Both gas lines and water pipes are not built straight. They are zig-zagged to take up motion and also they are made of segments separated by valves to isolate breaks. 4. Not all buildings can be built to the highest standards because it’s just too expensive. Retrofitting is a good approach.
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Questions
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1. What is LA's most earthquake resistant building? 2. Why is this building chosen to be the safest? 3. Why is it called a floating building? 4. How many suspension points are in the building? How do they move? 5. What size earthquake should the building be able to withstand? 6. How far is it designed to move? 7. Why aren't all buildings in Los Angeles designed like this?
Answers
1. The Emergency Management Department. 2. This is where all emergency management will take place to help the city recover. 3. The building is not attached to the ground. 4. 40; 20 move up and down and 20 move side to side 5. 8.0 6. 4’ side to side and 2’ up and down 7. The cost would be astronomical.
6.20 Staying Safe in an Earthquake
Review
Questions
1. What should you do to prepare for an earthquake? 2. What should you do during an earthquake? 3. What should you do after an earthquake?
Answers
1. Be sure that things will not fly or fall and hurt someone. Have an emergency kit ready. Know where to meet up with people and what you plan to do. 2. Stay away from anything that might fall on you whether you’re inside or outside. 3. Be careful of aftershocks, turn off your utilities, avoid dangerous situations.
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Questions
1. When is California's 4th season? 2. What should you do to prepare your home? 3. What should your emergency plan include? 4. What should an emergency kit include?
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Answers
1. No one knows when an earthquake will strike. 2. Insure that heavy objects won’t fly around or fall on someone. They should be anchored to something stable like the wall. Know where the utility shutoffs are. 3. You should have escape routes from each room and a meeting place for where you will meet up with other residents of your home. 4. Your emergency kit should include water, blankets, flashlights, food, prescription medication and first aid.
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