Answer Key to GIS Lab: Plate Tectonics: From the Inside Out!! A. Earthquake Patterns A half million earthquakes occur on the Earth each year. Many are small and go unnoticed, while others are large and can cause a great deal of damage. Earthquakes are one of the physical processes constantly changing the face of our dynamic planet. Other agents of change include volcanoes and faults. Do these processes occur anywhere on the Earth? Where do they occur? Go to the website http://arcims.mathsciencecenter.info and open the web based GIS mapping page titled Plate Tectonics by clicking on the picture to the right. A map of the world should be visible with layers on the right and tools on the left. Use your mouse to put a check in the Visible column and a dot in the Active column for Quakes95 like this:. Click located at the bottom of the Layers list. This layer shows 353 of the hundreds of thousands of earthquakes that occurred worldwide during 1995. Use your mouse to click on the Identify tool to the left. Now using your mouse click on one of the earthquakes in the map. A results box will appear showing the data for that particular earthquake. This data comes from the National Earthquake Information Center, a service of the U.S. Geological Survey that records moderate to large size earthquakes. 1. What information is given about each earthquake? Date, location, Latitude, Longitude, Magnitude, Depth and Time To find out more information, we can search through the data tables and determine the first earthquake or the strongest or weakest earthquake of 1995. To obtain this information we must conduct a query of the data. 2. To identify the first earthquake of the year you must: 3. 1. Make the Quakes95 layer active and visible like. 2. Click on the Query button. 3. Set the following Query builder options a. Field: DATE b. Operator: = c. Press the Get Samples button and should appear in Sample Values Box. d. Press the Add to Query String button. Check to make sure your window appears as below e. Press the Execute button 4. A list of the first earthquake of the year should appear in your window now. Plate Tectonics 1 http://mathinscience.info
2. Where did the first earthquake of the year occur and what was its magnitude? Off the East coast of Honshu, Japan: Magnitude: 6.2 The magnitude of an earthquake refers to its strength as measured by the Richter scale. The Richter scale is logarithmic, which means that an earthquake of magnitude 7.0 is ten times stronger than one of magnitude 6.0 and 100 times stronger than one of magnitude 5.0. The infamous San Francisco earthquake of 1906 had a magnitude of 8.3. Use the Query builder to answer questions 3 and 4. To identify the strongest earthquake of the year you must: 4. Make the Quakes95 layer active and visible like. 5. Click on the Query button. 6. Set the following Query builder options a. Field: MAGNITUDE b. Operator: > c. Press the Get Samples button and use the arrow key to select in Sample Values Box. d. Check to make sure your Operator did not change; if it did change it back to >. e. Press the Add to Query String button. Check to make sure your window appears as below f. Press the Execute button 4. A list of the strongest earthquakes of the year should appear in your window now. a. What is the highest magnitude earthquake in the Quakes95 data layer? 8.0 b. What is the lowest magnitude earthquake in Quakes95 data layer? 2.6 3. Visualizing geographic data on a map Trying to determine geographic patterns from just data in a table can be difficult. Creating a map with this data can make it easier for you to see the distribution of earthquakes. You will notice as you move your cursor over the map of the world in the bottom left hand corner of your browser sets of numbers will change. The first two sets of numbers are your longitude and latitude. 5. What does it mean if a longitude value is negative? A latitude value is positive? Negative longitude values indicate longitudes that are west of the prime meridian; Positive latitude values indicate latitudes that are north of the equator Plate Tectonics 2 http://mathinscience.info
6. Observe the map closely. What do you see? Is there a pattern in the way the earthquakes are distributed? Answers may vary. The earthquakes do appear to have a pattern to their distribution. 7. Briefly describe the pattern of earthquake distribution. The earthquakes appear to be clustered along the western coasts of North and South America as well as the eastern coast of Asia Use the Query builder to observe the pattern of high magnitude earthquakes for the Quakes95 layer. To observe the high magnitude earthquakes of the year you must: 1. Make the Quakes95 layer active and visible like. 2. Click on the Query button. Notice another window will appear. 3. Set the following Query builder options a. Field: MAGNITUDE b. Operator: > c. Type in 7 in the Values box like this:. d. Check to make sure your Operator did not change; if it did change it back to >. e. Press the Add to Query String button. Check to make sure your window appears as below f. Press the Execute button 4. All the earthquakes with magnitude greater than 7 will appear as large yellow dots on your map. 8. Where do high magnitude earthquakes tend to be located? Most of the high magnitude earthquakes appear to be concentrated to the east of Asia and to the north of Australia. The list of earthquakes you queried is below the map. Scroll to the bottom of the list. 9. How many earthquakes had a magnitude greater than 7.0 in 1995? 15 Zoom-in to one of your selected earthquakes. Click the identify button to get information about this earthquake. To quickly zoom back out to the full map, click the Zoom to Full Extent button. Plate Tectonics 3 http://mathinscience.info
10. What are the location, date and depth of your earthquake? Answers will vary. Let s take a look at all of the earthquakes that occurred from 1970 to 1993. Add the layer Quak7093 to your map by using your mouse to put a check in the Visible column and a dot in the Active column for QUAK7093 like this:. Click located at the bottom of the Layers list. 11. How are the earthquakes distributed? Briefly describe any patterns you see. About the same as in #7 Query the Quak7093 layer for earthquakes with a magnitude greater than 7.0 by clicking the query button. Use the same steps as we did to answer #10. (Hint: you can also click on the High Mag Quak layer) 12. Where do high magnitude earthquakes tend to be located? High magnitude earthquakes can be found along the western edges of North and South America, in a cluster north of India, and in a semi-circle from the east coast of Asia to north of Australia. C. Volcanoes, faults and plates Laying dormant for thousands of years, yet capable of violent eruptions with explosive ash or molten lava, volcanoes are another physical process constantly changing the surface of the Earth. Where do volcanoes occur in relation to earthquakes? Let s examine 919 major volcano locations around the world. Add the layer Volcano to your map by using your mouse to put a check in the Visible column and a dot in the Active column for Volcano like this:. Click located at the bottom of the Layers list. 13. How does the distribution of the volcanoes compare to that of the earthquakes? Describe any noticeable patterns. Volcanoes are most heavily concentrated along the western edges of North and South America, in a line bisecting Africa, and in a semi-circle from the east coast of Asia to north of Australia. The distribution is very similar to that of earthquakes. Zoom in on a volcano of your choice. Then use the Identify button and click on the volcano of your choice. 14. What are the name, elevation, and type of the volcano you chose? Answers will vary. Plate Tectonics 4 http://mathinscience.info
Now let s take a look at the Pacific Plate boundary. Add the layer PacificPlate to your map by using your mouse to put a check in the Visible column like this:. Click located at the bottom of the Layers list. The pattern of earthquakes and volcanoes surrounding the Pacific Ocean is known as the Ring of Fire. Put a dot in the Active column for World94 like this:. Use the Identify button to answer #15. 15. Identify three countries that border the Ring of Fire. Answers will vary but may include Canada, the United States, and Mexico Faults are cracks on the Earth s surface. Fault lines often stretch for miles and can sometimes be seen from the air. Let s look at where faults are located worldwide. Add and display the Faults layer like this:. Click located at the bottom of the Layers list. 16. How does the distribution of the faults compare to that of earthquakes and volcanoes? Describe any noticeable patterns. The highest concentration of faults coincide with the earthquake data. The upper portion of Earth s surface is made up of giant pieces, known as tectonic plates. The oceanic and continental land masses ride on top of these plates and move with them. Geologists have mapped the boundaries of these plates based on data such as those you have explored in this lesson. In fact, the pattern of earthquake and volcanoes was among the most important evidence in the development of the plate tectonics theory. Add and display the Plate_Lin layer like this: and click the Refresh Map button. This theme draws the lines of plate boundaries. Take the time to display different combinations of themes related to volcanoes, earthquakes, and faults by checking and unchecking the visible box and then click on. 17. How do the locations of earthquakes, volcanoes and faults compare to the plate boundaries? They all seem to be concentrated along the plate boundaries. Add and display the Plate_Pol layer. This layer displays the shapes of the plates labels the names of each plate. 18. Name all the plates that are shown on this map. Twelve plates are named: North American Plate, Pacific Plate, Cocos Plate, Nazca Plate, Caribbean Plate, South American Plate, Eurasian Plate, Arabian Plate, Phillipine Plate, African Plate, Indo- Australian Plate, Antarctic Plate. *Turn this layer off when finished by unchecking Plate_Pol layer and click Refresh Map Now let s figure out what percentage of earthquakes from 1995 occurred within 200 miles of our plate boundaries. To do this we will select the plate boundaries and then Buffer it to show all the Quake95 earthquakes within 200 miles. Plate Tectonics 5 http://mathinscience.info
To show all the earthquakes within 200 miles of a plate boundary you must: 1. Make just the Quakes95 layer visible like:. 2. Make the Plate_Lin layer visible and active like: 3. Click on the Select button. We want to select all the plate lines. Move your cursor to the upper left hand corner of the map and press your mouse button down but don t let up, as you do this drag your cursor to the bottom right hand corner of the map and release. As you drag you will notice a red box. The idea is we need all the plate lines to turn yellow meaning they are selected. 4. Click on the Buffer button. Notice the bottom window changes. a. Highlight features from: QUAKE95 b. Within a distance of: 200 miles c. Display attributes: Checked d. Check to make sure your box appears as below e. Press the Create Buffer button. This may take several seconds, be patient. 5. The window below the map will display the earthquakes within 200 miles of the plate boundaries. 19. If there are a total of 353 earthquakes in the Quake95 layer what percentage of earthquakes occurred within 200 miles of a plate boundary? 71% (251/353) 20. Do you think you would get a similar percentage if you buffered the layer Quak7093? Why or why not? Yes. This seems to be the major pattern around the world. 21. Why do you think earthquakes and volcano s occur most often near plate boundaries? Tectonic plates are in constant motion. The outward transfer of heat inside the earth drives convection circulation in the mantles that propel the plates across the surface of the earth. Some plates are sliding past each other. Others are moving apart. Still others are crashing into each other. Plate Tectonics 6 http://mathinscience.info