CH 5 & 6 Questions
docx
keyboard_arrow_up
School
Wilson College *
*We aren’t endorsed by this school
Course
107
Subject
Geology
Date
Apr 3, 2024
Type
docx
Pages
4
Uploaded by BarristerFlag10307
Morgan Kelly Environmental Geology
Chapters 5 & 6 Textbook Assignment 1. What is "elastic rebound" and how does it relate to earthquake motion?
Elastic rebound refers to the sudden release of accumulated strain energy along a fault line, typically during an earthquake. Over time, tectonic forces cause rocks on either side of a fault to deform elastically, storing energy as they bend and stretch. Eventually, the stress overcomes the frictional resistance along the fault, causing the rocks to suddenly snap back to their original shape, releasing the stored energy as seismic waves, which propagate outward, causing the ground to shake.
2. Distinguish among earthquake intensity, Richter magnitude, and moment magnitude. Which magnitude scale is most favored by seismologists today? Why?
Earthquake intensity refers to the subjective assessment of the effects of an earthquake on people, buildings, and natural features. Richter magnitude measures the amplitude of seismic waves recorded by seismographs. Moment magnitude measures the total energy released by an earthquake, taking into account the area of the fault rupture and the amount of slip. Moment magnitude is most favored by seismologists today because it provides a more accurate and consistent measure of earthquake size across a wide range of magnitudes. 3. Why should one be more concerned about the likelihood of an earthquake in Alaska than about one in Texas?
Alaska is located near multiple tectonic plate boundaries, making it prone to frequent and powerful earthquakes. In contrast, Texas is situated in the interior of the North American Plate, where seismic activity is generally lower.
4. In light of plate-tectonic theory, explain why devastating shallow-focus earthquakes occur in some areas and only moderate shallow-focus activity takes place in other areas.
Devastating shallow-focus earthquakes occur in areas where tectonic plates are actively colliding or sliding past each other. These areas often have locked faults that accumulate stress over time until they rupture catastrophically. In contrast, areas with only moderate shallow-focus earthquake activity may have less frequent or less intense tectonic activity, resulting in less strain accumulation and smaller, less frequent earthquakes.
5. How do scientists locate the epicenter of an earthquake?
Scientists locate the epicenter of an earthquake by analyzing the arrival times of seismic waves at multiple seismograph stations. By triangulating the arrival times, they can determine the epicenter, which is the point on the Earth's surface directly above the hypocenter, or the point where the earthquake originated.
6. What should people who live in earthquake country do before, during, and after an earthquake (the minimum?)
Before an earthquake, individuals should secure heavy objects, create an emergency kit, and have a family communication plan. During an earthquake, they should drop, cover, and hold on to protect themselves from falling objects and debris. After an earthquake, they should check for injuries, assess damage, and follow evacuation procedures if necessary.
7. If you were going to purchase a home, or go to work in a particular building, and were concerned about seismic safety, what information would you like to know before making a commitment?
Before committing to a home or building, one would like to know its seismic safety rating, construction materials and techniques used, adherence to building codes, and any previous history of seismic retrofitting or damage from earthquakes.
8. Describe the motion of the three types of earthquake waves discussed in this chapter and their effects on structures.
P-waves are compressional waves that travel fastest and can pass through solids and liquids. S-waves are shear waves that travel slower and can only pass through solids. Surface waves travel along the Earth's surface and cause the most damage to structures due to their larger amplitudes and longer durations.
9. What is the distinction between earthquake prediction versus forecasting? Which is more effective, and why?
Earthquake prediction involves forecasting the occurrence of earthquakes with specific details about location, magnitude, and timing, while earthquake forecasting provides probabilities of earthquakes occurring within a certain time frame and location. Forecasting is more effective because it focuses on probabilities rather than precise predictions, allowing for better preparation and risk assessment.
10. Why do wood-frame structures suffer less damage than un-reinforced brick buildings in an earthquake?
Wood-frame structures are more flexible and can absorb seismic energy without collapsing, whereas unreinforced brick buildings are rigid and prone to catastrophic failure during an earthquake.
11. What are the major kinds of volcanic landforms, and which types of eruptions create each kind?
Major volcanic landforms include shield volcanoes, stratovolcanoes (composite volcanoes), cinder cones, and calderas. Shield volcanoes are associated with effusive eruptions, stratovolcanoes with explosive eruptions, cinder cones with relatively small eruptions, and calderas with catastrophic eruptions.
12. How would you expect the eruption of a volcano that taps mafic (basaltic) magma to differ from the eruption of one that taps felsic (silicic) magma? What kind of rocks will result from each eruption?
Mafic (basaltic) magma tends to erupt effusively, producing lava flows with low viscosity and high fluidity. Felsic (silicic) magma tends to erupt explosively, producing pyroclastic flows, ash clouds, and volcanic domes. Mafic eruptions typically result in basaltic rocks, while felsic eruptions result in rhyolitic or andesitic rocks.
13. Explain the distribution of the world's active volcanoes in terms of plate tectonics theory.
The distribution of the world's active volcanoes is closely related to plate boundaries, including divergent boundaries, convergent boundaries, and hotspots. Volcanoes are commonly found along divergent and convergent boundaries where tectonic plates interact, as well as over hotspots, where mantle plumes upwell beneath the Earth's crust.
14. List the major kinds of volcanic hazards and discuss the steps that should be taken to avoid them or minimize their impacts on people.
Major volcanic hazards include lava flows, pyroclastic flows, ashfall, lahars (mudflows), and volcanic gases. Steps to avoid or minimize their impacts include implementing evacuation plans, constructing protective barriers, monitoring volcanic activity, and educating the public about hazards and safety measures.
15. In what way(s) can dormant volcanoes be especially dangerous?
Dormant volcanoes can become dangerous if they suddenly reawaken with explosive eruptions, catching nearby populations unaware and unprepared.
16. How do calderas form?
Calderas form when the roof of a magma chamber collapses into the chamber during a large volcanic eruption, creating a large, basin-shaped depression.
17. In what ways does volcanic activity benefit humankind?
Volcanic activity benefits humankind by contributing to the formation of fertile soils, providing geothermal energy resources, and supporting tourism and recreation.
18. If you were setting out to establish a program of monitoring a volcano to forecast its eruptions, what would you do?
Establishing a program to monitor a volcano for eruption forecasting would involve installing seismometers, GPS instruments, gas sensors, and other monitoring devices to detect signs of volcanic unrest, analyzing data to identify patterns and trends, and issuing timely warnings to at-risk populations.
19. What would you do to make a volcanic hazards map for people living around a volcano?
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
To create a volcanic hazards map, one would identify potential hazards such as lava flows, pyroclastic flows, lahars, and ashfall, assess their likelihood and potential impact areas based on historical eruptions and geological studies, and communicate the risks to local communities through maps, education programs, and emergency plans. 20. Contrast a volcano such as Mt. Rainier with one like Mauna Loa or Kilauea. Which, in general, would be the safer volcano to live around, and why?
Mt. Rainier is a stratovolcano prone to explosive eruptions and lahars, while Mauna Loa and Kilauea are shield volcanoes known for effusive eruptions. In general, living around shield volcanoes like Mauna Loa or Kilauea may be safer due to their less explosive nature and lower likelihood of catastrophic eruptions. However, both types
of volcanoes carry risks, and safety ultimately depends on factors such as distance from the volcano, local infrastructure, and preparedness measures in place.