Understanding Geologic Hazards: Earthquakes & Landslides

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 1/38 Laboratory 8: Geologic Hazards- Earthquakes and Landslides Due Dec 4 at 11:59pm Points 14 Questions 24 Available Nov 25 at 9am - Dec 4 at 11:59pm Time Limit None Allowed Attempts 2 Instructions This quiz was locked Dec 4 at 11:59pm. 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 ESS101 Lab 8: Geohazards ESS101 Lab 8: Geohazards You are allowed 2 attempts to complete this lab. A PDF copy of the lab is linked here: Link to Lab 8 PDF version (https://canvas.uw.edu/courses/1580211/files/95849651/download)

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 2/38 Attempt History Attempt Time Score KEPT Attempt 2 6 minutes 14 out of 14 LATEST Attempt 2 6 minutes 14 out of 14 Attempt 1 34 minutes 13.25 out of 14 Score for this attempt: 14 out of 14 Submitted Dec 4 at 9:42pm This attempt took 6 minutes. 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. 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

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 3/38 (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:

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 4/38 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?

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 5/38 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

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 6/38 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? 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

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 7/38 0.25 / 0.25 pts Question 4 What type of strain do you think the rocks in the picture below experienced? 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?

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 8/38 Source: https://www.smithsonianmag.com (https://www.smithsonianmag.com/science-nature/big-quakes- can-trigger-other-shakes-thousands-miles-away-180956985/) elastic 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

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 9/38 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

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 10/38 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! Strike-slip fault Earthquakes Stress and elastic strain can build up over time if the rock on either side of a fault continues to move while the fault plane remains locked (Figure 8- 3) . Once these stresses exceed the strength of the fault, the fault will slip very quickly and release elastic strain as seismic energy. This sudden release of energy is called an earthquake , and the location on the fault where the slip occurs is called the earthquake focus or hypocenter . The epicenter of an earthquake is the position on the surface of the Earth directly above the hypocenter. The vertical distance between the hypocenter and the epicenter is called the focal depth .

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 11/38 Figure 8-3 Schematic diagram showing the time transgressive process of a fault building up strain and stress and then releasing strain and lowering stress during an earthquake. Source: https://openpress.usask.ca/physicalgeology/chapter/12-1-what-is- an-earthquake-2/ (https://openpress.usask.ca/physicalgeology/chapter/12-1- what-is-an-earthquake-2/) Seismic Waves Following fault slip, seismic energy radiates away from the earthquake hypocenter in all directions (spherically) in the form of seismic waves . These waves are elastic, because they do not permanently deform the material that they travel through. There are two categories of seismic waves: body waves (travel through the Earth) and surface waves (travel along the surface of the Earth) ( Figure 8-4 ). Figure 8-4 Diagram showing body (S- and P-waves) and surface waves traveling away from an earthquake hypocenter. Source: https://www.seis- insight.eu/en/public-2/planetary-seismology/seismic-waves (https://www.seis-insight.eu/en/public-2/planetary-seismology/seismic-waves) There are two types of body waves called primary waves and secondary waves (Figure 8-5) . Primary waves, or P-waves , are compressional waves that compress and extend the material that they move through, displacing particles in the direction of wave propagation. Secondary waves, or S-waves , are shear waves that displace particles in the direction perpendicular to wave propagation.

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 12/38 Figure 8-5 Animations showing particle displacement due to passing P-waves (left) and S-waves (right). Note the little black box and how it deforms. Source: https://web.ics.purdue.edu/~braile/edumod/waves/Pwave.htm (https://web.ics.purdue.edu/~braile/edumod/waves/Pwave.htm) & https://web.ics.purdue.edu/~braile/edumod/waves/Swave.htm (https://web.ics.purdue.edu/~braile/edumod/waves/Swave.htm) As P- and S-waves reach the surface of the earth, they deform the ground beneath us and cause some of the shaking that we associate with an earthquake. P-waves travel through the earth faster than S-waves, hence the names primary and secondary. Therefore, the first shaking you experience during an earthquake is caused by the arrival of the P-wave. Surface waves are slower than body waves, arriving last and causing the most shaking during an earthquake. 1 / 1 pts Question 7 The figure above shows an earthquake (yellow star) that has occured on a fault adjacent to a house.

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 13/38 Answer 1: Answer 2: Answer 3: Answer 4: Answer 5: What important characteristics of the earthquake do A, B and C represent? A is the earthquake hypocenter . B is the earthquake focal depth . C is the earthquake epicenter . What type of fault did this earthquake occur on? normal Which seismic wave will reach the house first? p-wave hypocenter Correct! Correct! focal depth Correct! Correct! epicenter Correct! Correct! normal Correct! Correct!

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 14/38 p-wave Correct! Correct! The speed at which a seismic wave propagates through a material depends directly on the properties of that material. One important material property that impacts seismic wave velocity is density. Denser materials have more tightly packed molecular structures that allow seismic waves to quickly transfer energy between individual atoms and through a material. Conversely, less dense materials have more loosely built molecular structures that do not transfer energy as quickly, since the atoms are spaced farther apart. For this reason, seismic waves travel faster through denser material and slower through less dense material. In addition to material properties, the propagation style of a wave can impact how it travels through a medium. For example, the shear nature of S-waves does not allow them to travel through liquids. 0.25 / 0.25 pts Question 8 Do seismic waves travel faster through igneous rock (very dense) or sedimentary rock (not so dense) igneous Correct! Correct! sedimentary 0.25 / 0.25 pts Question 9 During an earthquake, would a house experience more shaking if it were built on top of bedrock or on top of loosely packed soil? bedrock

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 15/38 loosely packed soil Correct! Correct! Seismic Instruments Seismometers are instruments that record ground motion at seismic stations and can detect the arrival of seismic waves. Seismometers are extremely sensitive instruments that can record ground vibrations due to earthquakes thousands of miles away! Seismologists use the recordings from seismometers, or seismograms , to study many topics, including earthquakes, faults, the Earth’s interior, volcanoes, glaciers, rivers, and landslides. One fascinating result of seismic research is the discovery that the Earth’s outer core is liquid. In this case, seismologists noticed that S- waves were not arriving at certain stations after big earthquakes, and deduced that these S-waves must be getting stopped by some liquid body within the Earth. After some thought, they discovered that this liquid body must be the Earth’s outer core! Watch the 2-minute video below to learn more about this phenomenon and ‘seismic shadow zones’. 0:00 0.75 / 0.75 pts Question 10

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 16/38 Answer 1: Above is an example seismogram from a famous 1989 earthquake in California recorded at a seismic station in Finland. Time is on the x-axis and ground displacement is on the y-axis. Notice that the ground displacement is measured in microns (1/1000 of a millimeter!). Identify the arrival times of the different types of seismic waves. A represents the arrival of the P-wave . B represents the arrival of the S-wave . C represents the arrival of the surface waves .

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 17/38 Answer 2: Answer 3: P-wave Correct! Correct! S-wave Correct! Correct! surface waves Correct! Correct! Earthquake Scaling The size of an earthquake can be measured in several different ways, such as measuring the duration of shaking at a given point, measuring the maximum amplitude of the seismic waves generated by the earthquake, or measuring the area of the fault segment that slipped. The most common scale used for measuring earthquake size is the moment magnitude scale, denoted by M or Mw. The moment magnitude of an earthquake is described as: (1) where M0 is a variable called seismic moment, which depends on the characteristics of the earthquake and the type of rock in which it occurred. From equation (1), we can see that the moment magnitude scale is based on a logarithmic scale. In order to estimate the difference in energy released by two different magnitude earthquakes, we can apply the following equation: (2) where E is the energy released by the larger earthquake , E is the energy released by the smaller earthquake, m is the moment magnitude of the larger earthquake, and m is the moment magnitude of the smaller earthquake. Evaluating equation (2) with a Mw 1 and Mw 2 earthquake gives a change of energy ( E /E ) of ~32x. This means that each unit increase in Mw represents a 32-fold increase in the amount of energy released by an earthquake, which is directly related to the duration and intensity of shaking during an earthquake. w 1 2 1 2 1 2

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 18/38 0.25 / 0.25 pts Question 11 Using equation (2), how much more shaking would you expect from a Mw 8 earthquake versus a Mw 4 earthquake? 2x as much shaking 32x as much shaking 1,000x as much shaking 1,000,000x as much shaking Correct! Correct! Earthquakes in the Pacific Northwest Here in the Pacific Northwest (PNW), we live above the active Cascadia subduction zone. This tectonic setting means that PNW residents are vulnerable to three different types of earthquakes ( Figure 8-6 ): 1. Crustal earthquakes that occur in the North American plate 2. Slab earthquakes that occur in the descending Juan de Fuca slab 3. Subduction earthquakes that occur along the fault between the Juan de Fuca and North American plates

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 19/38 Figure 8-6 Cross-section through the Cascadia subduction zone, highlighting different types of earthquakes and the dates associated with large Mw events. Source: https://pnsn.org/outreach/earthquakesources (https://pnsn.org/outreach/earthquakesources) Crustal Earthquakes Subduction and other forces acting on the North American plate cause stress and elastic strain to build up within the crust. This accumulated elastic strain is intermittently released as shallow earthquakes along faults within the North American crust. A local example of crustal faults is the Seattle fault zone, a series of reverse faults running east-west directly through the city of Seattle ( Figure 8-7 ). The Seattle fault zone was last active ~1100 years ago (900 AD) and caused ~27 feet of vertical displacement between crustal blocks.

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 20/38 Figure 8-7 Map showing the locations of faults (red lines) in the Seattle fault zone. The location of UW is shown with a yellow star. Source: https://www.king5.com/article/news/local/disaster/why-you-should-be- prepared-3-big-earthquake-threats-in-pnw/281-457421137 (https://www.king5.com/article/news/local/disaster/why-you-should-be-prepared-3- big-earthquake-threats-in-pnw/281-457421137) Slab Earthquakes As the Juan de Fuca slab (the portion of the plate that has subducted) subducts beneath the North American plate and into the mantle, it begins to bend due to gravitational forces. This bending causes faulting, which results in deep earthquakes within the descending slab. The 2001 Mw 6.8 Nisqually earthquake is an example of a slab earthquake. Since the foci of slab earthquakes are relatively deep (>50km depth), the seismic wave energy from these earthquakes attenuate as the waves travel towards the surface. This means that the earthquake intensity (what is felt by the observer) for slab earthquakes is less than that of shallow earthquakes with equal magnitude. Subduction Earthquakes As the Juan de Fuca slab subducts, it drags the North American plate down with it. This is because the megathrust fault, which runs between the boundary of the Juan de Fuca and North American plates, is locked and does not allow the plates to move past each other. However, when the stress on the fault becomes too great, the fault fails and the two plates rapidly slide past each other, resulting in a subduction, or megathrust,

12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 21/38 earthquake. Megathrust earthquakes are typically the most destructive earthquakes we face, as they displace a large segment of the locked plate and the energy released results in >Mw 8 earthquakes. As the North American plate rebounds up during a subduction earthquake, it can displace large amounts of ocean water, causing another geologic hazard called a tsunami. In some cases, these tsunamis are large enough to travel large distances and impact countries on the other side of the Pacific Ocean. The most recent megathrust earthquakes and related tsunamis include the 2004 Indonesian and 2011 Japan events. The last megathrust earthquake along the Cascadia subduction zone occurred in 1700 AD. Washington Earthquake History Fortunately, most earthquake activity in the Pacific Northwest consists of low to moderate magnitude events (<6 Mw) that may be felt by local residents, but damage to structures and loss of life is correspondingly low. However, historically (1872-present) there have been moderate to high magnitude (> 6 Mw) earthquakes that have caused structural damage and resulted in fatalities. Table 8-2 ( EQTable (https://canvas.uw.edu/courses/1580211/files/95849556/download) ) and the map in Figure 8-8 ( EQMap (https://canvas.uw.edu/courses/1580211/files/95849567/download) ) below document larger earthquakes that have occurred regionally and were likely felt by residents in Washington State. Note that only earthquakes of these magnitudes (Mw 6 - 7), occurring in the Puget Sound region itself, would cause significant damage to structures and pose a seismic risk to local residents within the Puget Lowland region.

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 22/38 Table 8-2 Table of large earthquakes in Washington state. Figure 8-8 Map of Washington state, showing the epicenter locations and dates of earthquakes.

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 23/38 2 / 2 pts Question 12 Refer to Table 8-2 above. This table lists the largest known earthquakes felt in Washington State since 1872. Use this information to answer the following questions. Over the historical record (i.e., since 1872), how many earthquakes in the Puget Sound region (shown with bold font in Table 8-2) had magnitudes (felt or with instruments) greater than, or equal to 6.0 Mw (earthquakes that would be felt and pose potential seismic risks to residents living in the region)? 6 Assume that the earthquakes noted with unknown magnitudes (denoted with “?” in Table 8-2) are <6.0 Mw. What year was the first earthquake >=6.0 in the Puget Sound region documented in historical time?1909 What year was the most recent earthquake >=6.0 in the Puget Sound region?2001 On average how often does the Puget Sound region experience moderate to large earthquakes? This is called the recurrence interval (T) for moderate to large earthquakes.~25 years Use the time interval of the record (N) and divide it by the number of earthquake events >6.0 Mw (n) during that period. Note that the time interval of record extends until present. T = N/n If one of the unknown magnitude earthquakes (1880 or 1891) was >6.0 Mw, how would that change the recurrence interval?It would reduce it by 4 years You determined the recurrence interval of >= 6.0 Mw earthquakes that occur in the Puget Sound region. Does the time since the last large earthquake exceed its recurrence interval?no What is the shortest time interval between two earthquake events >= 6.0 Mw that have occurred in the Puget Sound region over the historical record (i.e., since 1872)? 3 years

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 24/38 Answer 1: Answer 2: Answer 3: Answer 4: Answer 5: Answer 6: Answer 7: Answer 8: Answer 9: (Assume that unknown magnitude earthquakes are < 6.0 Mw). What is the longest time interval between two earthquake events >= 6.0 Mw that have occurred in the Puget Sound region over the historical record (i.e., since 1872)?37 years (Assume that unknown magnitude earthquakes are < 6.0 Mw). Can you rely on the average recurrence interval data to predict the future occurrence of large (>=6.0 Mw) earthquakes to a specific year in the Puget Lowland?no 6 Correct! Correct! 1909 Correct! Correct! 2001 Correct! Correct! ~25 years Correct! Correct! It would reduce it by 4 years Correct! Correct! no Correct! Correct! 3 years Correct! Correct! 37 years Correct! Correct!

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 25/38 no Correct! Correct! 0.5 / 0.5 pts Question 13 Earthquake Intensity Earthquake intensity estimates (designated by Roman Numerals) are shown in Table 8-3 below ( Intensity Table (https://canvas.uw.edu/courses/1580211/files/95849588/download) ). Earthquake intensity measures the effects of an earthquake on different regions and is based on qualitative descriptions from observers. Intensity of an earthquake varies depending on the magnitude of the earthquake, the proximity to the earthquake’s epicenter, the substrate that underlies a region (i.e., bedrock versus saturated bay mud), and the duration of earthquake shaking. Earthquake intensity is measured using the Modified Mercalli Intensity Scale, first conceived by Italian volcanologist Giuseppe Mercalli in 1883, and modified by American seismologists Harry Wood and Frank Neumann (UW seismologist) in 1931. It has been further modified since 1931, but much of the original descriptions remain the same. Table 8-3 Modified Mercalli Intensity Scale for earthquakes.

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 26/38 Answer 1: Answer 2: Refer back to Table 8-2 to answer the following questions. Which earthquake intensity value is most frequently felt for moderate- large (Mw 6-7) earthquakes in the Puget Sound region? VII Which earthquake intensity value is locally felt for large (Mw >6.5) earthquakes in the Puget Sound region? VIII These earthquakes tend to cause significant damage to some structures, such as the Alaska Way viaduct (Highway 99), damaged in 2001 during the Nisqually earthquake, The Alaska Way viaduct has been replaced with the new tunnel. VII Correct! Correct! VIII Correct! Correct! 0.5 / 0.5 pts Question 14 Which of the three types of earthquakes that occur in the Pacific Northwest (crustal, slab, subduction) do you think could cause extensive damage to the metropolitan area of Seattle? More than one answer may be correct. megathrust earthquake on subduction zone Correct! Correct! low magnitude crustal earthquake on Seattle Fault high magnitude crustal earthquake on the Seattle Fault Correct! Correct! deep slab earthquake within Juan de Fuca plate

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 27/38 moderate magnitude earthquake on the South Whidbey Fault B. Landslides Mass wasting is defined as the downslope movement of earth materials under the influence of gravity. While mass wasting often erodes hillslope material slowly, as in soil creep, it can also happen at high speeds, disastrously impacting human lives and property. The classification of mass wasting is based on the type of movement (slide, fall, flow) and the composition of the moving mass (debris, mud, rock) ( Figure 8-9 ). We commonly refer to a number of these mass wasting processes as landslides. Figure 8-9 Mass wasting failure classification. From Hungr et al. 2013, originally from Cruden and Varnes 1996.

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 28/38 0.5 / 0.5 pts Question 15 Answer 1: Answer 2: Watch the video below of mass wasting in New Zealand. What is the composition of the moving mass? soil What type of movement is happening here? (consult Figure 8-9) flow soil Correct! Correct! flow Correct! Correct! Predicting where and when a slope will fail is an incredibly difficult task, but an understanding of what causes landslides can help us to mitigate risk. All hillslopes are in balance between forces acting to pull material down (gravity), and the forces acting to hold the slope material in place (cohesion, friction, and/or rock strength). Landslides are triggered when the forces acting to pull material down a slope overcome the forces

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 29/38 holding that slope in place. Processes that act to pull material down the slope include: the slope steepens (e.g. it is undercut by wave or stream erosion) the thickness (weight) of the material on the slope increases (e.g. due to sedimentation or construction) the density of the material on the slope increases (e.g. heavy rains fill the pore space with water) A landslide can also be triggered if the forces holding the material in place decrease. This occurs if: the cohesion of the material decreases, such that it does not stick together very well (e.g. due to shaking from an earthquake) internal friction decreases, making it easier for grains to start sliding past one another (e.g. water builds up along a plane of weakness) the pore water pressure increases (increased water in the pore spaces pushes grains apart) While a landslide can be triggered by changes to any of the above driving or resisting forces, if we are to assess landslide risk at a particular location, we must look at pre-existing conditions of the hillslope material. Some rock types are inherently weak and are referred to as incompetent rock . Some common examples of rocks that behave incompetently include shale, siltstone, mudstone, schist, and volcanic tuffs. Slope failures often exploit natural planes of weakness in the rock (e.g. faults, fractures, bedding planes, and foliation surfaces). Differences in porosity between rock units, which affect the rate at which water accumulates in pore space, can also make a slope more susceptible to failure. 0.5 / 0.5 pts Question 16 Watch the video below of a cliff topple in Cornwall, England. Note the fracture in the center of the cliff that begins to widen at 0:12. Watch how it propagates to the top and bottom of the cliff, forming the dominant slip plane of the failure. What was the triggering mechanism of this topple

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 30/38 Answer 1: Answer 2: undercutting by wave erosion ? Why are topples more likely than other forms of mass wasting at sea cliffsthe base of slope is eroded by wave processes causing failure from below ? North Cliffs Failure - Amazing Cliff Collapse caught on North Cliffs Failure - Amazing Cliff Collapse caught on … undercutting by wave erosion Correct! Correct! the base of slope is eroded by wave processes causing failure from below Correct! Correct! 0.5 / 0.5 pts Question 17

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 31/38 The devastating 2018 Hokkaido Iburi-Tobu earthquake triggered over 6000 landslides simultaneously. The underlying geology consists of volcanic soils interbedded with several layers of pumice. It was found that one particularly weak pumice layer liquefied during the intense shaking. What processes triggered these slides? (Choose all that apply) cohesion decreased Correct! Correct! cohesion increased internal friction decreased Correct! Correct! the slope steepened the thickness of material increased 0.25 / 0.25 pts Question 18 What was the ultimate cause of the landslides in Japan? (Choose all that apply.) incompetant rock Correct! Correct!

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 32/38 a layer of weakness Correct! Correct! seismic triggering Correct! Correct! 1 / 1 pts Question 19 Answer 1: The Lidar image above shows the region around Seattle, extending from the Puget sound to the foothills of the Cascades. Overlaid in brown are landslides mapped by the Washington State Department of Natural Resources. Note that most landslides in the Seattle area occur near the coast along the Puget Sound and Lake Washington. (a) Why are more landslides found along the coastline in Seattleslopes are over-steepened due to wave erosion ? The climate of the Puget Sound is characterized by high amounts of rainfall. As such, increased pore water pressure is the predominant landslide triggering mechanism in the puget sound. However, 1965 was a particularly dry year, yet there was a higher than average number of landslides in the Seattle area. (b) What was another possible trigger for these landslides earthquake event ? Include answers to both question (a) and question (b) in your response.

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 33/38 Answer 2: slopes are over-steepened due to wave erosion Correct! Correct! earthquake event Correct! Correct! Oso Landslide In March of 2014, a small community near Oso, Washington by the Stillaguamish river was buried by a sudden landslide. Forty-three people died - the deadliest landslide in U.S. history. The Stillaguamish river valley is filled with unconsolidated sand, clay and till deposited from glacial processes at the end of the last glacial period. Previously, it had been thought that landslides in the area occurred all at once, shortly after deglaciation. The 2014 event cast doubt on the assumed quiescence of landslide activity in the region. Figure 8-10 High-resolution Lidar image showing the location and ages of past landslides along the North Fork Stillaguamish River. From Lahusen et al. 2016 Take a look at Figure 8-10 , a high-resolution Lidar image (LaHusen et al. 2016) of the Stillaguamish River valley. Note the 2014 Oso landslide in

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 34/38 the center of the image. Also note the flat, high-elevation areas on the north and south side of the valley (Whitman Bench), which are formed from the deposition of glacial sediment. 0.5 / 0.5 pts Question 20 Note the flat, high-elevation areas on the north and south side of the valley, which are formed from the deposition of glacial sediment. This implies that the North Fork Stillaguamish River has cut down, or incised, into this sedimentary deposit. Which of the triggering mechanisms below is likely implicated in the failure of most or all of the stillaguamish landslides? Slope steepening and undercutting by stream erosion Correct! Correct! Increasing thickness of material on the top of the hillslope through sedimentation Seismic shaking increased housing development in the area 1 / 1 pts Question 21

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 35/38 The Oso landslide exposed the underlying lithology of the hillside, which features a unit of clay (deposited in a pro-glacial lake) covered by glacial outwash sand (meltwater deposits). Similar lithology is found throughout the Puget Sound and adjacent areas. Based on what you know about the physical properties of the two sediment units, how do you think this particular pre-existing condition increases the risk of landslides? the sandy outwash is permeable (water flows through it) and clay unit is impermeable, which perches groundwater and acts as failure plane Correct! Correct! the clay unit is permeable (water flows through it) and sandy outwash unit is impermeable, which perches groundwater and acts as a failure plane both the sandy outwash and clay units are permeable and allow groundwater to saturate the slope the sedimentological properties of the outwash sand and clay units played no role in the 2014 Oso landslide

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 36/38 1 / 1 pts Question 22 Answer 1: Answer 2: Answer 3: In Figure 8-10 , each landslide is colored by the estimated age of failure. To test the hypothesis that the Stillaguamish landslides failed shortly after the glacial retreat, which occurred approximately 16.4 thousand years ago, we can plot the total number of landslides through time based on their estimated age (same coloring as in F igure 8-10 ). From these data, is the rapid postglacial landslide hypothesis correctNo ? What time interval had the most dated landslides<500 years ago ? If you were a County planner or engineer would you recommend that high- density residential development could be zoned within mapped area shown on Figure 8-10No ? No Correct! Correct! <500 years ago Correct! Correct! No Correct! Correct! 0.25 / 0.25 pts Question 23 Using the plot of the number of landslide versus time, why might the number of landslides appear to be increasing over the past 2000 years compared to the earlier part of the Holocene (10,000 years to present) record? (more than one answer may be correct). recent landslides may obliterate the record of older landslides Correct! Correct! human development, such as logging may exacerbate landslide triggers Correct! Correct!

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 37/38 volcanic activity increased over the past 2000 years the early part of the Holocene may have been drier than the more recent Holocene record Correct! Correct! it took 8000 years for the Stillaguamish River to erode into the sediment record 0.5 / 0.5 pts Question 24 After finishing this class, you are contracted by the Washington State Energy office to work on hazard mitigation in the design process of a new nuclear power plant. Nuclear power plants are often placed near large bodies of water to take advantage of a cheap and abundant source of fluid to cool the reactors and to generate steam to power turbines. Several sites for the new plant have been proposed (above). To make a recommendation, you consult the Washington State Department of Natural Resources' map of geologic hazards. Note the active faults mapped with dotted lines, the tsunami hazard zones represented by yellow areas along the coast, volcanoes (brown) with volcanic mudslide zones (orange), and mapped landslides (multi-colored small dots and areas). Based on your knowledge of hazards and risk, where would be the best location to build the nuclear power plant? A B C

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12/12/22, 1:34 AM Laboratory 8: Geologic Hazards- Earthquakes and Landslides: ESS 101 B Au 22: Introduction To Geology And Societal Impacts https://canvas.uw.edu/courses/1580211/quizzes/1745128 38/38 D Correct! Correct! Quiz Score: 14 out of 14

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