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Chapter 6: Geological Activity and Earthquakes

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Chapter 6: Geological Activity and Earthquakes 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. Explore More Questions 1. How is rock laid down? 2. What is the law of superposition? 3. Why is the law of superposition important? CK-12 Earth Science Middle School Answer Keys - updated July 2019 1 ​ 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. Explore More Questions 1. What is a geologic fold and what causes one to form? 2. What types of forces create a set of folds? CK-12 Earth Science Middle School Answer Keys - updated July 2019 2 ​ 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. Explore More 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. CK-12 Earth Science Middle School Answer Keys - updated July 2019 3 ​ 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. Explore More 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. CK-12 Earth Science Middle School Answer Keys - updated July 2019 4 ​ 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. Explore More 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. CK-12 Earth Science Middle School Answer Keys - updated July 2019 5 ​ 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 Explore More 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 CK-12 Earth Science Middle School Answer Keys - updated July 2019 6 ​ 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.
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