Exercise 5 (Earthquakes and Plate Tectonics).docx

Exercise 5 (Earthquakes and Plate Tectonics).docx - General...

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General Earth Science Lab Exercise #5 Earthquakes and Plate Tectonics READINGS: Earth Science; chapters 7-8 OBJECTIVES: Upon completion of this exercise, the student should be able to: 1. Examine a seismogram and identify the P-waves, S-waves, and surface waves. 2. Use the time difference between earthquake waves to determine the distance to the epicenter. 3. Associate earthquake activity and focus depths with plate movement. 4. Associate the occurrence of volcanoes with hot spots or different plate-tectonic boundaries . Earthquakes Earthquakes are the result of motion along a fault plane caused by the build-up of stress. Waves of energy are produced as the ground ruptures at the focus of the earthquake. The focus is a point along the fault plane in the ground while the epicenter is located on surface directly above the focus. The waves of energy can be classified based on the particle motion and progression. Earthquake waves are recorded by seismometers at seismic stations all around the world. An example of a seismograph is given in Figure 8.9 of your textbook. P-waves , also known as primary waves, are the fastest moving of the earthquake waves and can travel through both solids and liquids because the particle movement is compressional. An earthquake also produces S-waves , or secondary waves. The S-waves can travel through solids because the particle movement is perpendicular to the wave propagation. Finally, surface waves are confined to the outer layer of the earth. These waves are slow moving in comparison to P-waves and S-waves but they may cause considerable damage Movements of P-waves and S-waves in the interior of the earth have been used to identify the layers associated with plate tectonics. These two types of waves can also be used to determine the distance between the seismic station and the epicenter of the earthquake. The time difference between the arrival of the first P-waves and the arrival of the first S-waves can be used along with the time travel curve. For example, using Figure 8.11 in the textbook, it can be determined that a time interval of five
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