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Back Lesson Print Plate Tectonics TEACHING TRANSPARENCY 54 Locations of Earthquakes in South America, 2002–2003 75ºW 60ºW 45ºW 30ºW 0º SOUTH AMERICA 15ºS 30ºS Earthquake Depth (km) PACIFIC OCEAN 0 25 ATLANTIC OCEAN 75 150 45ºS 300 600 Copyright © by Holt, Rinehart and Winston. All rights reserved. Back Lesson Print Name Class Date Transparency Worksheet Locations of Earthquakes in South America, 2002-2003 This map shows the locations and depths of earthquakes that registered magnitudes greater than 5 and happened in South America in 2002 and 2003. Use the map to answer the questions below. 1. Using the Key How many earthquakes happened at a depth greater than 300 km? 2. Analyzing Data Deep earthquakes are earthquakes that happen at a depth greater than 300 km. Which earthquakes happen more frequently: deep earthquakes or shallow earthquakes? 3. Making Comparisons How does the earthquake activity on the eastern edge of South America differ from the earthquake activity on the western edge? 4. Inferring Relationships The locations of earthquakes and plate boundaries are related. Where would you expect to find a major plate boundary? 5. Identifying Trends In what part of South America do most deep earthquakes happen? What relationships do you see between the locations of shallow and deep earthquakes in South America? 6. Analyzing Relationships Most deep earthquakes happen when subducting plates move deeply into the mantle. What type of plate boundary is indicated by the earthquake activity in South America? Explain your answer. Copyright © by Holt, Rinehart and Winston. All rights reserved. Holt Earth Science Plate Tectonics Back Lesson Print ANSWER KEY 2. shallow earthquakes 3. In the time period shown, no earth- 2. The denser oceanic crust is subducted under the less dense continental crust, where it releases water, causing the mantle above to melt. Some magma may rise through the continental crust and form volcanic mountains. 3. The plates are sliding horizontally past each other at a transform boundary. 4. The buildup of tension between sticking plates would produce the most severe earthquake along a transform boundary. 5. The top diagram shows crust being created at a mid-ocean rift; the center diagram shows crust being “ destroyed” at a subduction zone. quakes with magnitude greater than 5.0 occurred on the east coast, but many occurred on the west coast. 4. along the western coast of South America 5. Most deep earthquakes happen toward the center of the continent. As you move east from the west coast, the earthquakes tend to get deeper. 6. The plate boundary on the west coast of South America is probably a convergent boundary (subduction zone). The subducting plate is moving eastward under the continent. As the subducting plate moves down under the continent, the earthquakes get deeper because the plate boundary is deeper. 52 Ridge Push and Slab Pull 1. The older crust is denser because it’s shown sinking beneath the newly formed crust. 2. Ridge push moves crust away from the mid-ocean ridge. 3. the plate to the left, which is subducting 4. its greater density 55 Isostatic Adjustment 1. Isostasy is the balance between the forces of gravity and buoyancy that allows Earth’s crust to be stable. 2. weathering or erosion of surface rock 3. The lithosphere rises to compensate and regain the balance. 4. The growth of an ice sheet would cause the lithosphere beneath the ice to sink, and the ocean floor to rise. The retreat of a glacier would cause the land underneath the melting glacier to rise, and the ocean floor to sink. 53 The Supercontinent Cycle 1. Siberia and North America were 2. 3. 4. 5. located on the equator; North America and Europe were differently shaped islands; and Africa, South America, and Antarctica comprised one continent. about 20 million years Answers may vary. Sample answer: The development of a single landmass would have vastly reduced the amount of coastal areas, which generally support a great diversity of marine species, and instead formed an enormous open ocean with relatively little coastline. You might expect them to continue to separate, moving across the Pacific and perhaps colliding and forming a single landmass once again many years from now. somewhere in what is now the Pacific Ocean, based on the current rate of tectonic plate movement 56 Types of Stress 1. Stress is the force acting on the 2. 3. 4. 5. lithospheric rock, such as squeezing, stretching, and twisting. its volume is reduced and it is pushed higher up or deeper down into the crust Tension stretches and pulls rock apart, and the rock becomes thinner. Shear stress acts on rock by pulling in opposite directions, tension stretches and pulls, and compression squeezes and shortens. Shear stress, because of the horizontal movement of tectonic plates past each other 57 Folds 54 Locations of Earthquakes in South America, 2002-2003 1. the plane that slices a symmetrical 1. about 11 fold into two symmetrical halves Copyright © by Holt, Rinehart and Winston. All rights reserved. Holt Earth Science 14 Answer Key