Suppose you have been hired you to develop a hazard map and awareness brochure to provide to incoming freshmen here at CofC.

Transcription

1 Introductory Geology Team names Lab 2: Earthquakes and Earthquake Hazards Materials and Vocabulary Materials: Pencil and eraser, lab manual, calculator, containers, core samples, pennies, laptops Vocabulary and Concepts - You are responsible for understanding the following: a. Epicenter f. P-waves b. Focus g. S-waves c. Fault h. L-waves d. Seismic Waves i. Travel-time curve e. Seismograph and Seismograms I. IT COULD HAPPEN TOMORROW It Could Happen Tomorrow, a TV documentary from The Weather Channel, takes a close look at incredible acts of nature, which could cause havoc across America. Part drama, part science, and part history, It Could Happen Tomorrow searches the past for clues to theoretical weather events still to come and explores the potential impact on our modern world. Speculate with your teammates what Charleston would be like if an earthquake of the same magnitude as the that occurred in 1886, MM 7.3, happened today.how would the devastation differ from what happened in 1886? Would it be worse or less? Why? II. WHAT EXACTLY IS AN EARTHQUAKE? Suppose you have been hired you to develop a hazard map and awareness brochure to provide to incoming freshmen here at CofC. What types of information do you need to develop this map and brochure? Go to and click on EARTHQUAKES. NOTE: Spend some time in this website exploring sections 1-6; do not complete section 7- we will complete that section later in the lab. Some of this information can be found in your lab manual in Chapter What is an earthquake? 2. Where do earthquakes typically occur? 1

2 3. What is the difference between the FOCUS and the Epicenter? 4. Name the three main types of waves. 5. Which arrives at the recording station or seismograph first? 6. How many seismograph readings do you need to determine the epicenter? 7. Is Charleston located on a current plate boundary? If not, please describe why there are earthquakes here? For a quick review on how earthquakes relate to Plate Tectonics, lets take a look at the following Figures from your lab manual, Figure 2.2, page 25, and answer the following questions: Figure 2.2 Use the figure above and your lab exercise from last week to help you complete the table below. Boundary Type Divergent Type of Earthquake Fault (normal/reverse/strikeslip) Type of Volcanism (fissure/composite/none) Topographic features (volcanic island arcs, ridges, trenches, fracture zones, subduction zones, mountain belts) Sketch of boundary motion Convergent Transform 2

3 III. MEASURING AND RECORDING AN EARTHQUAKE Go to Chapter 16, pages in your lab manual to help you with the following questions. 8. Using Figure 16.7 on page 399, answer the questions below: a. How long does it take a P-wave to travel 8,000km? minutes b. How long does it take a S-wave to travel 8,000km? minutes c. How long does it take a Love-wave to travel 8,000km? minutes d. Which wave arrived at the seismometer FIRST? e. How do you know? The travel-time curve can be used to calculate average velocities (rates) of seismic waves that have traveled from the focus to a seismic station. f. Note that the Time on the Travel Time graph is recorded in MINUTES. However, most earthquake seismic wave velocities are recorded in KILOMETER PER SECOND. What do you need to do in order to solve this problem? g. Examine the point where the P-wave curve crosses the 1000-km distance mark. What was the average velocity the P-wave traveled? (Show your work.) km/sec h. What is the average velocity of the P-wave recorded at a 6500-km seismic station? km/sec i. What is the average velocity of the S-wave recorded at a 10,000-km seismic station? km/sec j. What is the average velocity of the L-wave recorded at a 10,000-km seismic station? km/sec Very good! Now that you have a basic understanding of how seismic waves are generated and recorded, you and you teammates will learn how to utilize that data to actually locate where an earthquake occurred. 3

4 IV. WHERE DID THAT COME FROM? LOCATING AN EARTHQUAKE. Prior to the invention of seismograms, the ringing of church bells was one of the first signs that an earthquake occurred. In the late 1800s, a major earthquake took place in the continental United States. Church bells rang in New York, Boston, Chicago, and Miami as a result of this massive earthquake. Listed below are the times when these church bells rang and the time when this earthquake took place. Given the information that P-waves (which ring church bells) travel at a rate of 8.0 km/sec, you and your teammates will use that rate to determine the location of the epicenter of the earthquake. SHOW YOUR WORK! Note: the times are measured to the tenths of a minute, thus 26.2 minutes is NOT 26 minutes and 2 seconds, but rather 26 minutes and 2 tenths of a minute. 1. Church bells rang in the nearest city at 9:51 pm. distance = 0 km 2. In Chicago church bells rang at 9:53.6 p.m. (latitude = longitude = ) Time = sec Distance = km 3. In Boston church bells rang at 9:53.7 p.m. (latitude = longitude = ) Time = sec Distance = km 4. In New York church bells rang at 9:53.1 p.m. (latitude = longitude = ) Time = sec Distance = km 5. In Miami church bells rang at 9:52.6 p.m. (latitude = longitude = ) Time = sec Distance = km 6. Use Google Earth to determine the location of the earthquake. Use the website (try using a different browser if you are not able to connect) and scroll down to the options. Enter your radius in kilometers. Input latitude and longitude. Click on Draw Radius. Repeat for the other 3 cities. 7. What major city is closest to the epicenter of your earthquake? 4

5 V. HOW DOES THE TYPE OF EARTH MATERIALS AFFECT EARTHQUAKE DAMAGE? In this section of the lab exercises, you and your teammates will explore how various types of earth foundation materials can dramatically affect the type of damages that can occur to buildings on the surface during an earthquake. 1. You will first explore several interactive scenarios to learn how materials behave under different magnitude earthquakes. Work through part seven of to determine the best scenario for building in an earthquake prone area and fill out the table below. Ground Type Magnitude Result Bedrock High Landfill High 2. The second website allows more detailed interaction with the different types of building construction in addition to the various types of foundation materials. Use one of the following weblink to access the Earthquake simulator: Explore to determine more detailed scenarios for building in earthquake prone areas. Try varying the Ground Type and Prevention Mechanism to determine which has the most impact on how destructive the earthquake is. Make sure to read the text after the simulation and don t just describe the picture. The text has vital information about each scenario. Fill out the table below. Ground Type Magnitude Prevention Mechanism Coastal Superquake Reinforced masonry Result Coastal Superquake Superquake 3. The Scenario Coastal, Superquake, Reinforced Masonry at is the same scenario as Charleston for the most part. Why didn t we have a tsunami after the 1886 earthquake? 4. For the Scenario Coastal, Superquake: Given the parameters of the earthquake type and soil (Coastal, Superquake), what style of building construction would be the safest? 5. For the Scenario Superquake: Given the parameters of the earthquake type (Superquake) and best building style from above, what type of earth foundation materials would be the safest during a superquake? 5

6 6. Out of all the types of earthquakes, building prevention mechanisms, types of foundations, which scenarios would generate the MOST DEVASTASTION? VI. EARTH MATERIALS UNDERNEATH MUSC AND THE COLLEGE OF CHARLESTON The Department of Geology has recently acquired two core samples (a core is a cylindrical section of sediments and rock that has been extracted from a drilled area) one from the outer edges of the Charleston Peninsula (near MUSC) and one from the inner peninsula (near College of Charleston). For the purposes of this lab exercise, our instructors developed simulations of these cores for you to study. There are 6 sets of these core samples. Examine the materials in the samples and write a short description of each layer (chart below). The sample with artificial fill is from location A (MUSC) and the other from B (CofC). CORE LOCATION A- MUSC B -COFC ARTIFICIAL FILL NOT APPLICABLE MODERN BARRIER ISLAND NOT APPLICABLE ANCIENT BARRIER ISLAND COOPER MARL 6

7 7. Based on your observations, make a hypothesis as to the location on which you would build. A- MUSC or B -COFC 8.Why? 9. Out of each layer, which would be the most stable during an earthquake? Artificial Fill Modern Barrier Island Ancient Barrier Island Cooper Marl 10. Why? After you have described the core sample layers, your team can begin to test each layer as to how it stands up under an earthquake simulation. Pay particular attention to which foundation materials experience liquefaction and predict how buildings would survive in those regions. Follow the steps and answer the questions below. Step 1: Take the container of artificial fill. Place several pennies in the ground type, imitating the vertical walls of buildings or structures constructed on uncompacted sediments. Simulate an earthquake by gently hitting the container on the table. Observe what happens to the buildings. 11. What happened to the buildings in the artificial fill sediments during your simulated earthquake? 12. Why? Step 2: Repeat step 1 with each of the ground types. 13. What happened to the buildings in the modern barrier island sediments during your simulated earthquake? 14. Why? 15. What happened to the buildings in the ancient barrier island sediments during your simulated earthquake? 16. Why? 17. What happened to the buildings in the cooper marl sediments during your simulated earthquake? 18. Why? Step 3: Gently hit the graduated cylinder with the simulated core for location A- MUSC on the table and simulate an earthquake. 19. What happened to the house with the foundation directly on the artificial fill? 20. What happened to the house with the foundation drilled to the cooper marl? 7

8 Step 4: Gently hit the graduated cylinder with the simulated core for location B -COFC on the table and simulate an earthquake. 21. What happened to the house with the foundation directly on the ancient barrier island deposit? 22. What happened to the house with the foundation drilled to the cooper marl? Summary: 23. Which foundations experience liquefaction? 24. Why? 25. Which cores are more stable during earthquakes MUSC or COFC? 26. Why? 26. What recommendations would you suggest to Mayor Riley to help develop new codes for building developers in these areas, based on what you learned from these lab exercises today? 8