Chapter 9 Plate Tectonics Investigation 9 Modeling A Plate .

NameChapter 9ClassDatePlate TectonicsInvestigation 9Modeling a Plate BoundaryIntroductionThe lithosphere is divided into moving segments called plates. Theplates move as units relative to all other plates. All major interactionsoccur among individual plates along boundaries. Scientists firstattempted to outline the plate boundaries by using locations ofearthquakes. Later research showed plates bounded by three distincttypes of boundaries, which exhibit different types of movement.A convergent boundary is formed when two plates slowly movetogether. At this boundary, the leading edge of one plate is bentdownward, sliding beneath the second plate. This process is calledsubduction, and the convergent boundaries are called subductionzones. The surface expression produced by one plate sliding belowanother plate is an ocean trench.Just south of the Aleutian Islands in the northern Pacific Ocean,the Pacific plate moves northward and is subducted beneath theNorth American plate. A large number of earthquakes occur in thisregion. In this investigation, you will use earthquake data from onepart of this region to form a model of the convergent boundarybetween the two plates.Problem Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.How can you use earthquake data to model a convergent boundarybetween two plates?Pre-Lab DiscussionRead the entire investigation. Then work with a partner to answer thefollowing questions.1. Posing Questions Write a question that summarizes the purposeof this investigation.2. Controlling Variables What is the dependent variable in thisinvestigation?Earth Science Lab Manual 79

NameClassDate3. Controlling Variables What is the independent variable in thisinvestigation?4. Inferring Why should the graph of earthquake depth vs.earthquake latitude have a zero at the top of the vertical axis?5. Predicting How do you think earthquake depth is related to thedistance from an ocean trench?Materials(per pair of students)rulerprotractorResource 3 in the DataBankProcedureVolcanic island arcTrenchFigure 1Oceanic crustContinental crustOceanic eaocrephe100 km200 kmEarth Science Lab Manual 80 Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.1. Examine the map on Resource 3 in the DataBank. Study theconvergence of the Pacific plate and the North American platejust south of the Aleutian Arc of volcanic islands in the northernPacific Ocean.2. Draw and label a diagram showing how the edges of the Pacificplate and the North American plate converge. Use Figure 1 tohelp you draw this diagram.

NameClassDate3. The Data Table below shows the depths of foci and latitudes ofearthquakes in the Aleutian Islands. All of the earthquakes in thetable occurred near 180 W longitude. Examine the table ofearthquake data and record any patterns you observe. Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.DATA titude of Epicenter ( 3251.7751.1552.13Depth of Focus 5579111804. Use the information in the Data Table to construct a graph showingthe location and depth of the earthquakes. Use the following grid andplot the latitude on the horizontal axis and the depth of the focus onthe vertical axis. Number the vertical axis with zero at the top andmaximum depth at the bottom. Give your graph an appropriate title.5. After plotting the data, draw a straight line that comes as close aspossible to each of the data points.Earth Science Lab Manual 81

NameClassDateTitle:Degrees North LatitudeDepth of Focus 40150160170180190200210220230240250Analysis and Conclusions2. Analyzing Data How does the graph illustrate that the boundarybetween the Pacific plate and the North American plate is aconvergent boundary?3. Applying Concepts The Aleutian trench is located where the twoplates meet at the surface of the lithosphere. Use the graph todetermine the approximate latitude of the Aleutian trench at 180 Wlongitude. Explain your answer.Earth Science Lab Manual 82 Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.1. Using Graphs What relationship exists between the depths of theearthquake foci and the latitude?

NameClassDate4. Using Graphs Use the slope of the graph to determine howquickly the convergent boundary descends as latitude increases.5. Calculating A change in latitude of one degree corresponds to adistance of approximately 111 km along a north–south line. Usingthis information and your answer to Question 4, determine how farthe convergent boundary descends as it moves 1 km northward.Show your work. Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.Use your results from Question 5 to help you answer Questions 6 and 7.6. Using Models Draw a triangle that shows a side view of theconvergent boundary with the correct scale relationship betweenhorizontal distance and depth. Measure the angle at which thesubducted plate descends beneath the upper plate. This is calledthe subduction angle.Earth Science Lab Manual 83

NameClassDate7. Calculating Imagine there is a volcanic island arc on the surface ofthe lithosphere above the area where the descending plate reaches adepth of 100 km. Approximately how far north of the trench are theislands located? Show your work.8. Evaluating and Revising Are all of the data points you plotted onthe graph close to the straight line you drew to best fit the data?Provide possible explanations for your answer.9. Applying Concepts Is the year in which an earthquake occurredan important variable in this investigation? Explain.The United States Geological Survey provides earthquake data fromlocations around the world. Obtain earthquake data near a divergentboundary such as an oceanic ridge or a transform fault boundary suchas the San Andreas Fault. Graph some data points to see whether thedepths of the foci of the earthquakes change as the distance from theboundary increases. Compare your findings to the results from thisinvestigation. Explain any differences.Earth Science Lab Manual 84 Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.Go Further

Pre-Lab Discussion Read the entire investigation. Then work with a partner to answer the following questions. 1. Posing Questions Write a question that summarizes the purpose of this investigation. 2. Controlling Variables What is the dependent variable in this investigation? Earth Science Lab Manual 79