Analyze Can you locate an earthquake's epicenter? - legacyjr.net

Name Date ClassSkill PracticeAnalyzeLESSON 1: 45 minutesCan you locate an earthquake’s epicenter?Imagine the room where you are sitting suddenly begins to shake. This movement lasts forabout 10 seconds. Based on the shaking that you have felt, it might seem like an earthquakehappened nearby. But, to locate the epicenter, you need to analyze P-wave and S-wave datarecorded for the same earthquake in at least three different locations.Learn ItWhen scientists conduct experiments, they make measurements and collect and analyzedata. For example, seismologists measure the difference in arrival times between P-wavesand S-waves following an earthquake. They collect seismic wave data from at least threedifferent locations. Using the difference in arrival times, or lag time, seismologists candetermine the distance to an earthquake epicenter.Try It1. Read and complete a lab safety form.2. Obtain a map of the United States, seismograms, and an earthquake distancegraph from your teacher.Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.3. Study the three seismograms in your textbook. Determine the arrival times, to thenearest second, of the P- and S-waves for each seismometer station: Berkeley, CA;Parkfield, CA; and Kanab, UT. Record the location and the arrival times for P- andS-waves.4. Subtract the P-wave arrival time from the S-wave arrival time and record the lag time.5. Use the lag time and the Earthquake Distance graph in your textbook to determine thedistance to the epicenter for each seismometer station.6. Use the map scale to set the spacing between the pencil and the point on the drawingcompass equal to the distance to the first seismometer. Draw a circle with a radiusequal to the distance around the seismic station on the map.7. Repeat for the two other seismometer locations. The point where the three circlesintersect marks the earthquake epicenter.Earthquakes and Volcanoes 25

Name Date ClassSkill Practice continuedApply It8. Consider the difference between the arrival times of P-waves for all three seismometerlocations. Why does this difference occur?9. Examine the calculated lag times for all three seismograms. Why do you think thearrival-time differences are greater for the stations that are farthest from the epicenter?10. Where did the earthquake occur?11. Key Concept Why does it take three seismograms to locate an earthquakeepicenter? What is this process called?Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.26 Earthquakes and Volcanoes

Answers continuedLesson 1, Skill PracticeBerkeleyBoulderNewYorkCityPhoenixUNITED STATESOklahoma CityKnoxvilleHoustonNMiami0500 kmCopyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Earthquakes and VolcanoesT15

Name Date ClassKey Concept Builder LESSON 1EarthquakesKey Concept Where do earthquakes occur?Shallow earthquakeDeep earthquakeDirections: Refer to the map to help you circle the term in parentheses that correctly completes each sentence.Earthquakes occur in many places throughout the world. Though most earthquakes areCopyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.(1.) (shallow/deep), some earthquakes occur (2.) (on the surface of/deep inside) Earth. Deepearthquakes occur along convergent boundaries where Earth’s (3.) (tectonic plates/surfacelayers) collide. These earthquakes occur at depths (4.) (greater/less) than 100 km. When thishappens, the denser oceanic plate sinks into the (5.) (mantle/core). These deep earthquakesare typically (6.) (less/more) destructive than earthquakes that occur along (7.) (divergent/convergent) plate boundaries because of the amount of (8.) (lava/energy) released when theplates collide. Earthquakes that occur along divergent plate boundaries are considered to be(9.) (shallow/deep) earthquakes. Here the Earth’s tectonic plates (10.) (push together/pull apart). An example of a divergent plate boundary is the (11.) (mid-ocean/continental)ridge system.The collision of Earth’s tectonic plates can form large (12.) (coral reef/mountain) ranges,such as the Himalayas in Asia. Most earthquakes, however, do not occur in the middle ofcontinents. Instead, they occur in (13.) (oceans/rivers) and along the (14.) (edges/forests) ofcontinents. These areas have active plate boundaries where earthquakes result from thebuildup and release of (15.) (vibrations/stress) as rock pushes against rock.Earthquakes and Volcanoes 21

Name Date ClassChallengeLESSON 1Interior of EarthGeologists have used the properties of the P-waves and S-waves generated by earthquakesto predict the composition of Earth’s interior. Figure 1 is a graph of the behavior of P-wavesand S-waves as they travel through Earth’s layers.Directions: Use the graph to answer each question.MantleDensity (g/cm 3 )2.7–3.3200S-wavesP-waves5.51,0002,000No S-wavesin outercore10–123,0004,000Depth (km)5,000Outer core12–130 2 4 6 8 10 12 14Inner coreVelocity (km/s)6,0001. How fast do P-waves move in the crust?2. How fast do S-waves move in the crust?3. What happens to S-waves approximately 2,900 km below Earth’s surface?4. What does the behavior of S-waves between the depths of approximately 2,900 km andapproximately 5,100 km tell you about the outer core?5. How does the velocity of P-waves change as they travel through the mantle, outer core,and inner core?Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.24 Earthquakes and Volcanoes