Salvadori s Guide to Talking with Your Students

Transcription

1 SALVADORI'S GUIDE TO TALKING WITH YOUR STUDENTS EARTHQUAKES

2 SALVADORI'S GUIDE TO TALKING WITH YOUR STUDENTS EARTHQUAKES Introduction...1 Exercise 1: The Cracked Egg...2 Exercise 2: Falling Towers...3 Exercise 3: Scraping Plates...4 Exercise 4: Liquefaction Game...5 Questions to Ask Your Students...6 Vocabulary...7 Resources...9

3 Part 1: Salvadori s Guide to Talking with Your Students is intended to help you have a conversation with your students about natural disasters. Hands-on exercises can help students understand the phenomenon. Also included is a vocabulary list and a list of resources for further exploration and earthquake safety. Why the earth quakes: The earth s crust is like a broken eggshell, and the pieces are called plates. Plate tectonics the movement of the earth s crust create bands that contain fault lines. These giant plates are constantly shifting in relation to each other, causing the earth to quake. How do earthquakes affect people? Approximately 1.3 million earthquakes happen around the world every year, but most are too small to affect us. On average, there is only one earthquake of 8.0 magnitude (or higher) every year; these earthquakes release more energy during fault ruptures and can be hazardous. The figure below shows that strong earthquakes occur mainly on the West Coast of the United States. Though New York City does not sit on a seismically active fault line, moderate earthquakes are a possibility (on average, NYC has one every one hundred years). The strongest one was recorded at 5.2 magnitude in 1884, and another was recorded at 2.4 magnitude in Figure courtesy of USGS: The ground-shaking generated during an earthquake is unlikely to affect people directly (besides startling or frightening them). It is what these ground motions can do to the natural and man-made environments around us that can significantly affect us. So, while the possibility of a strong earthquake occurring in New York City is low, the risk is heightened by a huge population, the number of structures in the city, and the intricate, aging infrastructure. In New York City s metro area, building codes require buildings to be designed to withstand the Maximum Considered Earthquake (one with a two percent chance of happening at any point within a 50-year period). Salvadori has put together some activities that will help you explain to your students how the earth moves and what happens to the built environment during an earthquake. Questions for discussion Has anyone experienced an earthquake? If so, what was it like? If the continents are constantly shifting, what do you think will happen to them over time? 1

4 Exercise 1: The Cracked Egg In this experiment you will use a boiled egg to simulate the behavior of the tectonic plates on the earth s surface. You ll Need 1 pre-cooked egg 1 clock or timer The Exercise Strike the boiled egg, and break the eggshell into a number of pieces, some large and some small. They will be the tectonic plates of your earth. If you now squeeze the egg gently between two fingers, the plates will move. Some will bump against adjoining plates, others will slide along them, and some will move away from each other. A plate may even slide under an adjoining plate. Tectonic plates diagram 2

5 Exercise 2: Falling Towers To show how earthquakes can damage buildings and harm people, try this demonstration. You ll Need 8 wooden cubes 1 helper The Exercise Have your helper erect two towers, with three or four wooden cubes each, on the back of one or both of your hands, as shown in fig FIGURE 1.1 Push your hands together and suddenly let them slide against each other (fig. 1.2). The cube towers will likely collapse. FIGURE 1.2 Now imagine that the wooden towers were buildings and your hands were tectonic plates. The devastation can be immense. 3

6 Exercise 3: Scraping Plates Using only hands, this experiment allows you to feel how tectonic plates bump into each other and create earthquakes. You ll Need 2 hands (you can do this by yourself or with a classmate) The Exercise Make both hands fists with the knuckles bulging out. The backs of your hands will be your plates and the knuckles will represent the rough edges of the tectonic plates. Push your knuckles together and at the same time try to make one hand slide up and against the other. The harder you push your knuckles together, the harder it will be to make your hands slide; you will feel the stress increase along your knuckles, just as it increases between the rough edges of the plates. If you keep pushing for a while, the muscles of your plates will start hurting because the knuckles are preventing the sliding. But eventually one plate will suddenly slide, releasing the energy accumulated in your hands. This is how an earthquake happens. 4

7 Exercise 4: Liquefaction Game This experiment will show you what happens to a building set on weak soil during an earthquake. You ll Need 1 brick 1 pail sand (enough to fill the pail) water (enough to cover the sand) The Exercise First, fill the pail with the dry sand and set a brick vertically on the sand surface. If you shake the pail slightly, as if it were hit by an earthquake, the brick may shake but it will not collapse. Now fill the pail with water to just above the sand s surface (the sand should be fully saturated with water). If you shake the pail now, as you did before you poured in the water, the brick will slowly sink into the sand, tilting or toppling over or even disappearing (fig. 1.1). The brick behaves like a tall building on mushy soil and shows how the water acts as a lubricant, allowing the brick to slide into the sand. The same phenomenon takes place when a building is set on weak soil, particularly on soil near a sandy seashore where it is completely saturated (fig. 1.2). FIGURE 1.1 FIGURE 1.2 5

8 Questions to Ask Your Students Re-cap What is an earthquake? What causes earthquakes? How do earthquakes cause damage? Does the earth open up during an earthquake? Where do earthquakes occur? What is the intensity of an earthquake? Can people cause earthquakes? Does a small earthquake mean that a larger earthquake is coming? Magnitude What is the magnitude of an earthquake? What is the difference between the magnitude and the intensity of an earthquake? Is there a maximum magnitude for an earthquake? At what magnitude do earthquakes begin to be felt? At what magnitude does damage start to occur? How many magnitude scales exist? Why? What are they called? Distribution and Frequency of How often do earthquakes occur? Where can I find information on the world's earthquakes? Are earthquakes really on the increase? If so, why? What is the largest recorded magnitude of an earthquake in world history? In Your State How often do earthquakes occur in your state/country? Where do earthquakes occur in your state/country? Do damaging earthquakes occur in your state/country? What is the largest earthquake ever recorded in your state/country? Follow-up: Research Topics for Your Students What is the relationship between volcanoes and earthquakes? Will more shocks be felt after a strong earthquake? Can earthquakes be predicted? Does the rate of earthquakes increase in cold weather? Are there certain months of the year that are more seismically active than others? Certain earthquakes have a negative magnitude, is this an error? 6

9 Vocabulary Note: Most words are included (and highlighted) throughout the text; we also included additional words your students may hear in the media. Aftershock a small earthquake that follows the main earthquake Amplitude the measure of peaks between waves on a seismograph Compression a forces that pushes on or squeezes a material Deformation the bending, tilting, and breaking of the Earth s crust; the change in the shape of rock in response to stress Earthquake Epicenter a term used to describe a sudden slip on a fault and the resulting ground shaking and radiated seismic energy caused by the slip; volcanic or magmatic activity, or other sudden stress changes in the earth the point on the earth s surface directly above an earthquake s center Fault a break in the earth s crust along which movement can take place, causing an earthquake Intensity a measure of the degree to which an earthquake is felt and the amount of damage caused by an earthquake Liquefaction a process by which water-saturated sediment (such as sand) temporarily loses strength and acts as a fluid Magnitude a number that characterizes the relative size of an earthquake, based on measurement of the maximum motion recorded by a seismograph 7

10 Plate tectonics the theory that considers the earth's crust to be composed of several large, thin, relatively rigid plates that move in relation to one another Richter scale a scale used to measure the energy released in an earthquake Seismic activity the types, frequency, and size of earthquakes that happen over a period of time in a specific area Seismic wave a wave of energy that travels through the Earth, away from an earthquake in all directions Seismograph a device that measures the strength of an earthquake Seismology the study of earthquakes Shearing stress that pushes masses of rock in opposite directions, in a sideways movement Tectonic plates the large, thin, relatively rigid plates that move in relation to one another on the outer surface of the Earth Tension a force that pulls on a material Tsunami an extremely large wave caused by an earthquake 8

11 Resources For more information and hands-on activities about earthquakes, visit Salvadori s store: For more information about earthquakes and New York City, visit: r_4.8_earthquakes.pdf For information about earthquake safety and preparedness at home, visit FEMA s site: For more information about the Salvadori Center: Phone: thecenter@salvadori.org 9