Laboratory 8_ Geologic Hazards- Earthquakes and Landslides_ ESS 101 B Au 23_ Introduction To Geology

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12/6/23, 3:41 PM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 23: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1664976/quizzes/1922407 1/24 Laboratory 8: Geologic Hazards- Earthquakes and Landslides Due Dec 10 at 11:59pm Points 14 Questions 24 Available Nov 24 at 9am - Dec 10 at 11:59pm Time Limit None Allowed Attempts 2 Instructions Attempt History Attempt Time Score KEPT Attempt 2 1,048 minutes 14 out of 14 LATEST Attempt 2 1,048 minutes 14 out of 14 Attempt 1 83 minutes 12.22 out of 14 Score for this attempt: 14 out of 14 Submitted Dec 6 at 3:40pm This attempt took 1,048 minutes. Learning Objectives By completing this lab, students will: Understand the difference between stress and strain and how both influence rock deformation Learn why earthquakes occur and why we experience shaking during an earthquake Gain insights into what factors promote landslides Recognize why the Pacific Northwest is prone to certain geologic hazards You are allowed 2 attempts to complete this lab. Introduction Most of the geological processes that we have covered in previous labs take place over thousands or millions of years. Many of these processes are impossible to observe during our lifetimes and have little direct effects on our everyday lives. In this lab, we are going to focus on geologic processes that can occur almost instantaneously and that profoundly impact our lives and the landscapes we live in. In particular, we will explore the processes that produce earthquakes and landslides, two phenomena that pose serious geologic hazards in the Pacific Northwest.
12/6/23, 3:41 PM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 23: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1664976/quizzes/1922407 2/24 1 / 1 pts Question 1 Laboratory Honor Statement Cheating or plagiarism of any kind will not be tolerated in ESS 101. This includes copying answers from a friend or classmate, copying answers verbatim found on the internet or other literary sources, or copying any work that may answer the question being asked. Make sure you always use your own words when answering the questions in the homework and cite appropriate references if you use them to help you answer the question. Anyone caught violating the academic code of conduct (https://www.washington.edu/cssc/for-students/academic-misconduct/) will receive a “0” grade on the assignment, and if the conduct is deemed egregious, reported to the UW Academic Misconduct representative. I acknowledge that I have carefully read and understand the above statement regarding the consequences of cheating and plagiarism, and promise to complete my work in this class with honesty and integrity. Answer "True" below supporting your acknowledgement. True Correct! Correct! False A. Earthquakes and Faults Stress and Strain As you learned in Lab 2, the Earth’s crust is broken up into tectonic plates. The movements of these plates exerts great forces, termed stresses , at their boundaries. Importantly, not all stress is the same. The specific type of stress produced from the motion of a given plate depends directly on the type of plate boundary. For example, a divergent boundary will produce a different stresses than a convergent boundary. In addition, stress can be placed on rocks within a plate (rather than at a boundary) from a variety of sources, such as a glacier pushing down (compressing) a section of a plate. Generally, we can divide stress into three categories: tension, compression, and shear . Figure 8-1 below illustrates each of these: Figure 8-1 Diagrams illustrating the three different types of stress . Source: https://earthquake.usgs.gov/learn/glossary/? term=compressional%20stress (https://earthquake.usgs.gov/learn/glossary/?term=compressional%20stress) As you can see Figure 8-1 , each type of stress represents a different force. As you can see in the figure, each type of stress represents a different force. Tensional stress is equivalent to forces pulling rocks apart, while compressional stress is equivalent to forces pushing rocks together. Shear stress is different from each of these, as it forces rocks to slide past one another. 0.25 / 0.25 pts Question 2 Look at the outcrop picture below. Which type of stress do you think produced the structure in these rocks?
12/6/23, 3:41 PM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 23: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1664976/quizzes/1922407 3/24 Source: http://www.geologyin.com/2015/02/rock-deformation-causes-and-types.html (http://www.geologyin.com/2015/02/rock-deformation-causes-and-types.html) compression Correct! Correct! tension shear The manner in which a rock deforms in response to stress is called strain . Just as there are multiple types of stress, there are different categories of strain. The type of strain experienced by a rock depends on a number of variables, including the composition of the rock, how long it is under stress, the rate at which it is stressed, and the temperature and pressure at which it is stressed. Generally, we can divide strain into three groups: elastic, plastic, and brittle . Moving from elastic to plastic to brittle, the change in the shape of the rock becomes more extreme. Elastic strain will produce a temporary change in the rock structure, where the rock returns to its original shape after the stress is removed. Plastic strain will produce permanent changes in the rock’s structure without breaking the rock, such as folds. Brittle strain will also produce permanent changes, but will do so by fracturing and breaking the rock. 0.25 / 0.25 pts Question 3 During the last ice age (about 12,000 years ago), much of North America was covered by glaciers. Today, we can still observe the strain that those glaciers imparted on the rocks below them. The figure below illustrates this, showing the vertical velocities of the crust in North America, increasing from blue to red. What type of strain do you think the glaciers caused?
12/6/23, 3:41 PM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 23: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1664976/quizzes/1922407 4/24 source : https://www.rncan.gc.ca/sites/www.nrcan.gc.ca/files/earthsciences/pdf/geomatica.pdf (https://www.rncan.gc.ca/sites/www.nrcan.gc.ca/files/earthsciences/pdf/geomatica.pdf) elastic Correct! Correct! plastic brittle 0.25 / 0.25 pts Question 4 What type of strain do you think the rocks in the picture below experienced?
12/6/23, 3:41 PM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 23: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1664976/quizzes/1922407 5/24 Source: https://www.canyonministries.org/bent-rock-layers/ (https://www.canyonministries.org/bent-rock-layers/) elastic plastic Correct! Correct! brittle 0.25 / 0.25 pts Question 5 What type of strain do you think the rocks in the picture below experienced? Source: https://www.smithsonianmag.com (https://www.smithsonianmag.com/science-nature/big-quakes-can-trigger-other-shakes-thousands-miles-away-180956985/) elastic
12/6/23, 3:41 PM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 23: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1664976/quizzes/1922407 6/24 plastic brittle Correct! Correct! Faults Now that we understand what forces are at play at tectonic boundaries, and how those forces affect the rocks found there, we can focus on an example particularly relevant to the Seattle area. About 200 miles off the coast of Seattle, the Juan de Fuca and North American plates meet. As we saw in Lab 2, they form a convergent boundary. Using what we’ve just learned, we can say that the stress at this plate boundary is compressional . However, the strain experienced by the rocks near us is a bit more complex. As mentioned above, the type of strain that a rock experiences depends on a number of variables. This means that in a system as large and complex as the Juan de Fuca-North American boundary, rocks will experience all three types of strain. Therefore, we can assume that the rocks around us can build up elastic strain, bend, and fracture. When rocks fracture, they can produce faults. Continued force applied to those faults can then create earthquakes. To better understand how earthquakes happen, we need to know how rocks on either side of a fault move. Two important terms that are useful for explaining fault motion are the hanging wall and the footwall . The hanging wall overlays the footwall, as illustrated below in Figure 8-2 : Figure 8-2 A fault block showing the hanging wall, footwall and motion on a fault. Source: (https://archive.usgs.gov/archive/sites/geomaps.wr.usgs.gov/parks/deform/ghangft.html) https://archive.usgs.gov/archive/sites/geomaps.wr.usgs.gov/parks/deform/ghangft.html In Figure 8-2 , the relative motion of the hanging wall and footwall is shown with the arrows in the middle. Here, the hanging wall is moving up relative to the footwall. We classify faults based on the relative motion of the hanging wall and footwall, as summed up in Table 8-1. Sometimes, the two sides of a fault do not experience relative motion vertically , but experience it horizontally , where one side moves in a different cardinal direction than another. For example, one side may move north, while the other moves south; we call these strike-slip faults. Motion of Hanging Wall Motion of Footwall Fault Name Down Up Normal Fault Up Down Reverse Fault Horizontal Horizontal (opposite) Strike Slip Fault Table 8-1 Fault names and the motions of their hanging walls and footwalls. 0.5 / 0.5 pts Question 6 The type of fault that is produced in rocks depends directly on the type of stress that is applied to those rocks. Knowing this, what type of fault do you think results from the convergence of the Juan de Fuca and North American plates? (Hint: Which direction would the arrows in the above figure be pointing relative to each other given the motion of each wall?) Normal fault Reverse fault Correct! Correct!
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