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EARTHQUAKES OUR RESTLESS PLANET 1 videocassette 22 minutes Copyright MCMXCV Rainbow Educational Media 4540 Preslyn Drive Raleigh, NC 27616-3177 Distributed by: United Learning 1560 Sherman Ave., Suite 100 Evanston, IL. 60201 800-323-9084 www.unitedlearning.com www.unitedstreaming.com PRINCIPAL CREDITS Producer, Writer and Director: Peter Matulavich Consultants: Jim Mori, Ph.D. Scientist in Charge United States Geological Survey Michael Worosz, M.A. Curriculum Consultant Associate Producer: Videography & Animation: Production Manager: Special Thanks to: Diann Fried Peter Matulavich Roxanne Hall United States Geological Survey National Geophysical Data Center KTVUTV Video and Teacher's Guide produced for Rainbow Educational Media by Peter Matulavich Productions San Dimas, California TABLE OF CONTENTS Introduction 2 Objectives 3 Summary 4 Review Questions 7 Discussion Questions 9 Activities 12 Glossary 14 Bibliography 16 Script 20 INTRODUCTION This video is designed to introduce students to the subject of earthquakes, their causes and their effects. Few natural forces create such destruction and instill such awe as earthquakes, yet it has been only in recent years that scientists have determined the primary cause of earthquakes: the grinding of the tectonic plates which compose our planet's shell. Students will learn through exciting, full-motion animation that the earth's plates move as a result of movement in the material that makes up the earth's mantle. The mantle movement isn't slow and gradual, but rather occurs in spurts when sufficient stress builds up along faults in the earth's crust, and one side of the fault lurches past the other. The energy that is released is in the form of seismic waves which move outward in all directions, not unlike the waves that occur when a stone is tossed into a pond. When seismic waves reach the earth's surface they can cause considerable destruction and loss of life. In the video's conclusion, students will learn that scientists continually study and monitor earthquakes in the hope that they might someday be able to forecast earthquakes, thereby reducing potential destruction and loss of life. 2 OBJECTIVES After viewing this video, students should know: • the names of the earth's interior layers • the concepts of continental drift and plate tectonics • the cause of plate movement • the three types of plate boundaries • the location and importance of the midocean ridge • the locations and importance of subduction zones • the cause of most earthquakes • the devastating power of some earthquakes • areas where earthquakes are most likely to occur • the location of the San Andreas fault • types of monitoring equipment used by scientists to study earthquakes • how earthquakes are measured 3 SUMMARY The video opens with dramatic scenes of the Loma Prieta earthquake of 1989. Students learn that while the quake lasted only 15 seconds, 67 people were killed and damage was widespread. The narrator poses these questions: What causes earthquakes? Why do earthquakes occur in some places but not in others? Will scientists ever be able to forecast earthquakes? Next, we see students examining a large globe. As useful as globes are they are unable to tell us what's inside our planet. Full motion animation then reveals the various layers of the earth's outer shell, the lithosphere, which consists of the crust and the rigid, outer portion of the earth's mantle. Students leam that the earth's shell is cracked into more than a dozen pieces called plates, and that each plate carries a continent, or an ocean basin, or sometimes both. The positions of these plates are only temporary. They are moving at an average rate of one to four inches a year in a variety of directions, carrying continents and ocean basins with them. Animation reveals what the continents looked like millions of years ago and how they slowly reached their presentday positions. Animation also shows what the world will look like millions of years in the future as the continents continue their slow dance around the globe. The video then discusses what causes the plates to move: the circulating movement of magma within the earth's mantle. Students learn that in some places, plates covering ocean basins are moving apart and, as they do, magma rises from the mantle to fill the gap. 4 This process is referred to as sea-floor spreading and the area where magma rises is known as a mid-ocean ridge. A mid-ocean ridge circles the globe, generating new plate material along its length. The video discusses how plate movement along the mid-ocean ridge is responsible for numerous underwater earthquakes. Earthquakes also occur near other types of plate borders: subduction zones and transform faults. Subduction zones are areas where one plate dives, or subducts, beneath another. Transform faults are areas where plates slide past each other. We learn that the grinding of plates has been going on for so long that the earth's crust is filled with cracks referred to as faults, and it is in these faults that earthquakes originate. Faults are locked in place most of the time, but when enough stress builds up, the fault will suddenly slip, one side sliding past the other, releasing energy in the form of seismic waves. The waves generated in earthquakes are similar to the waves created when a stone is tossed into a pond. If the disturbance is big enough, seismic waves reach the earth's surface where they can cause considerable destruction. We learn that the place where a fault slips is called the earthquake's focus and the point of the earth's surface directly above the focus is called the earthquake's epicenter. Next, the video discusses the work being conducted by earthquake scientists. We follow a scientist into the mountains where he buries a seismometer (a monitoring device) which will be part of an earthquake monitoring network. Next, the video segues to a control room where powerful computers receive data from hundreds of buried seismometers. The computers help scientists determine the location and size of an earthquake. 5 Students will then see that different types of seismic waves are associated with earthquakes. Animation shows the characteristics of P (primary) and S (secondary) waves. The video concludes with the discussion that millions of people live in seismically-active areas and that's why scientists hope that they will one day be able to forewarn people of impending earthquakes. 6 REVIEW QUESTIONS 1. What are the earth's interior layers? The layers are the inner core, the outer core, the mantle and the lithosphere or shell. 2. What composes the lithosphere? The lithosphere is composed of the crust and upper portion of the mantle. 3. The lithosphere is broken into more than a dozen pieces. What are these pieces called? They are called tectonic plates. 4. What causes the earth's tectonic plates to move? The movement of plates is caused by the movement of magma within the mantle. 5. What is the difference between magma and lava? Lava is the name for magma after it erupts from volcanoes. 6. What is the mid-ocean ridge? It is an area where two plates move apart allowing magma to rise and fill the resultant gap. 7. What are subduction zones? Subduction zones are areas where one plate dives beneath another, becoming consumed back into the earth's mantle. 7 8. What causes earthquakes? Earthquakes are caused by sudden movements along faults. 9. Seismic waves can be compared to what other types of waves? They can be compared to the waves created when a stone is tossed into a pond. 10. What is the earthquake's focus? The place where a fault slips is referred to as the earthquake's focus. 11. What is the earthquake's epicenter? It is the point on the earth's surface directly above the focus. 12. What is a seismometer? It is a device used to measure the amount and degree of shaking during an earthquake. 13. What is the Richter scale? It is a scale used to gauge the magnitude of an earthquake. 14. Can scientists forecast earthquakes? No, but they hope they will be able to do so in the future. 8 DISCUSSION QUESTIONS These questions are designed to encourage classroom discussion 1. While not discussed in the video, ancient peoples attributed earthquakes to a variety of unscientific causes. For example, Hindu mythology describes an earth supported by eight mighty elephants. An earthquake would result when one of the elephants bowed its head. Explain the occurrence of earthquakes as they might've been explained by ancient peoples. Answers include earthquakes being attributed to angry gods venting their anger; the jostling caused by giant animals and beasts; and various supernatural explanations. 2. The video discusses why earthquakes occur in some areas but not in others. What is the likelihood of an earthquake occurring in the area in which you live? Answers, of course, vary with each locality. Many earthquakes occur in California, Alaska, and other Pacific states. One of the country's largest earthquakes occurred in Missouri over a century ago, and no area is immune to earthquakes. 9 3. The video depicts the tremendous devastation, loss of life and injuries caused by earthquakes. What earthquake safety precautions can people take to minimize injuries, damage, and death? While not discussed in the video, there are numerous safety precautions and many rely greatly on common sense. A few include: - staying calm, not panicking. - seeking protection under heavy tables, beds, door jams -securing heavy objects, i.e. bookcases, mirrors, water heaters - knowing where and how to shut off the gas in the event of a gas leak - maintaining emergency food and water - avoiding damaged structures 4. The video discusses plate tectonics as the mechanism behind the occurrence of earthquakes. What other natural phenomena can be explained by plate tectonics? Continental drift, volcanism, and mountain building can all be explained by plate tectonics. 5. Earthquakes occur throughout the world with frightening regularity. Ask students to recall and discuss earthquakes -with which they are familiar. Answers might include: 1994 Northridge, California; 1989 Loma Prieta, California ; 1976 Tangshan, China; 1971 San Fernando, California; 1964 Anchorage, Alaska; 1948 Fukui, Japan; 1906 San Francisco. 10 6. Many people, including scientists, believe that animals can sense an impending earthquake. What could explain this ? While no one can say with certainty how, or even if, animals can sense an impending earthquake, it is common knowledge that many animals have keener senses than humans and some have abilities which we do not. For example, catfish are believed to be sensitive to vibrations . Some people believe dogs, horses, and snakes to be similarly sensitive. 7. Many of the casualties and much of the destruction experienced in some earthquakes are not the results of earthquakes themselves, but occur afterward. What are some other hazards directly associated with earthquakes? Fires from broken gas lines, landslides from weakened ground, and floods from broken dams, have all contributed to earthquake destruction and casualties. 8. The video discusses that someday, scientists may be able to forecast the occurrence of earthquakes. What benefit would a 24-hour earthquake warning provide a city? While some lives might be saved, others might be lost in the panic to escape the city. 11 ACTIVITIES These activities are designed to encourage students to learn more about some of the things covered in the video. 1. The video discusses how stress builds along a fault before it slips with a sudden jerk. Activity: This can be simulated by having students press their hands together and then try to slide one past the other. Often, their hands will slip with a sudden jerk. Students can also bend sticks until they suddenly snap. 2. P and S waves were discussed in the video as the first two types of seismic waves to reach the earth's surface. Activity: Students can mimic the motion of P waves by stretching a slinky and then allowing it to retract. Coils of the slinky will alternately stretch and contract, much like the motion of P waves. Activity: Students can mimic the motion of S waves by tying one end of a long rope to an object, and then jerking the other end with a whip-like motion to create a wave that travels the length of the rope. 3. The video discusses that an earthquake's destructive capability is greater near the epicenter. 12 Activity: Have students set up about a dozen dominoes on top of a large cardboard box. Next, have a student thump one end of the box, observing which dominoes are the first to fall. Generally, the dominoes closest to the thumping will fall first. 4. The video discusses several devastating earthquakes such as the Loma Prieta earthquake of 1989. Activity: Have students research and report on a devastating earthquake. 5. The video discusses how earthquakes occur along plate boundaries. Activity: Have students draw a map of the world, marking plate boundaries and locating recent earthquakes. 13 GLOSSARY continental drift: theory that continents can drift convergent boundary: boundary where two plates come together crust: thin outermost layer of the earth destructive: able to cause great damage divergent boundary: boundary where two plates move apart epicenter: point on the earth's surface that lies directly above an earthquake's focus fault: crack in a rock, one or both sides of which have moved in relationship to the other focus: point within the earth where movement along a fault creates an earthquake inner core: solid innermost layer of the earth lava: molten rock that erupts from the earth lithosphere: outer layer of the earth composed of the crust and outermost portion of the mantle magma: name for lava before it reaches the earth's surface magnitude: size of an earthquake measured by the amount of energy released mantle: mostly molten layer of the earth located below the crust 14 mid-ocean ridge: undersea mountainous ridge and divergent plate boundary that circles the earth outer core: molten layer of the earth located below the mantle P wave: first seismic wave to reach the earth's surface Richter scale: scale used to measure the magnitude of earthquakes San Andreas fault: 500-mile-long transform fault that divides California seismic wave: shock wave caused by an earthquake seismogram: record made by a seismometer seismometer: instrument used to record the movement of the ground during an earthquake shell: informal name for the lithosphere subduction zone: convergent boundary where one tectonic plate descends beneath another S wave: second seismic wave to reach the earth's surface tectonic plates: rigid moveable sections of the lithosphere transform boundary: boundary where two plates slide past each other 15 BIBLIOGRAPHY Ballard, Robert D. Exploring Our Living Planet. National Geographic Society, Washington, D.C., 1983. Bernstein, Leonard and Wong, Harry K. Earth Science, 2nd ed. Globe Book Co., New Jersey, 1979. Calder, Nigel. The Restless Earth. Viking Press, 1972. Cattermole, Peter and Moore, Patrick. The Story of the Earth. Cambridge Univ. Press, 1985. Clark, John. Earthquakes to Volcanoes. Gloucester Press, New York, 1992. Editors of Time-Life Books. Volcano. Time-Life Books, Alexandria, VA, 1982. Erickson, Jon. Rock Formations and Unusual Geologic Structures. Facts on File, Inc., New York. Erickson, Jon. Volcanoes and Earthquakes. Tab Books, Inc., 1988. Frances, Peter and Jones, Pat. Images of Earth. Prentice Hall, Inc., New Jersey, 1984. Harris, Stephen L. Fire and Ice. Pacific Search Press, 1980. 16 Harris, Stephen L. Agent of Chaos. Mountain Press Publishing Co., Missoula, Montana, 1990. Kaye, Glen. Hawaii Volcanoes. KC Publications, 1976. Lutgens, Frederick and Tarbuck, Edward. Essentials of Geology, 4th ed. Macmillan Co., New York, 1989. Marvin, Ursula. Continental Drift. Smithsonian Institution Press, 1973. Mather, Kirtley F. The Earth Beneath Us. Random House, New York, 1964. Miller, Russell. Continents in Collision. Time-LifeBooks, Alexandria, VA., 1983. Redfern, Ron. The Making of a Continent. Times Books, New York, 1986. Simpson, Brian. Minerals and Rocks. Galahad Books, New York, 1974. VanCleave, Janice. Earthquakes, Spectacular Science Projects. John Wiley & Sons, New York, 1993. VanCleave, Janice. Volcanoes, Spectacular Science Projects. John Wiley & Sons, New York, 1994. Van Rose, Susanna and Marcer, Ian F. Volcanoes. British Museum, 1991. Van Rose, Susanna. Volcano & Earthquake. Alfred A. Knopf, 1992. Walker, Bryce. Earthquake. Time-Life Books, Alexandria, VA., 1982. Weiner, Jonathan. Planet Earth. Bantam Books, New York, 1986. 17 Wright, Thomas and Takahashi, Taeko and Griegs, J.D. Hawaii Volcano Watch. Univ. of Hawaii Press, 1992. Zike, Dinah. The Earth Science Book. John Wiley & Sons, Inc. 1993. 18 SCRIPT In 1989, a major earthquake strikes Northern California. While the quake lasts only 15 seconds, 67 people are killed and damage is widespread. Each year, thousands of earthquakes occur throughout the world. While most are minor, a few cause great damage and loss of life. What causes the earth to rumble and shake? Why do some areas of the world experience earthquakes and others do not? Will scientists ever be able to forecast earthquakes? We're all familiar with a globe. It shows what our planet looks like from the outside. It shows the great land masses, called continents, and the bodies of water, called oceans. As useful as globes are, they are unable to show you one very important part of our planet, the inside. The earth's interior consists of several different layers: the inner core which is believed to be solid iron and which is very hot; the outer core which is believed to consist of rocky material so hot and under such great pressure that it is in a liquid state; the mantle which is not so hot as the outer core and not so liquid. The mantle's outermost portion is solid. This is the solid outer portion of the mantle. Above this, the outermost layer of the earth, the crust. Together, the crust and the solid outer portion of the mantle form the earth's outer shell. They are referred to as the lithosphere. 20 It's not always easy to see the earth's crust. It is covered by vegetation and oceans; but if you could drain the earth's oceans and strip away our planet's vegetation, the earth might look something like this. Now we can see the earth's hard outer shell, and if you look closely, you can also see where the shell is cracked. The red glowing lines mark the places where the earth's shell is cracked into small and large pieces called tectonic plates. Each plate carries a continent, or an ocean basin, or sometimes both. The plates are moving at one to two inches a year in a variety of directions, carrying continents and ocean basins with them. Millions of years ago, the earth looked something like this, every continent in a different position. They were so close together, they formed a single, super continent, called Pangaea; but even then, the plates were moving, a few inches a year, and kept moving, until they reached their present-day positions. The theory that continents move is called continental drift. When you look at a globe today, you are looking at only a moment in time, because the continents are still moving, inches a year, too slow to see, as they move farther and farther apart. Then the continents will stop moving apart. They will change directions, coming together once again. Millions of years from now, scientists expect the world to look entirely different; every continent in a new position, carried there by the moving plates. 21 While we can't see this movement occurring, we can see the effects. Earthquakes are just one of several dramatic effects of plate movement. Here's why the plates are moving. Scientists believe material in the mantle is circulating much as it is doing here. The movement may be caused by heat within the mantle. You can get an idea of how heat can cause a circulating movement, by watching rice as it boils. What you see happening within this beaker is similar to what's happening within the earth's mantle. As mantle material moves, perhaps only inches a year, it causes the plates above it to move as well. In some places, plates are moving in opposite directions. They are moving apart. The area where two plates are moving apart is called a divergent boundary. Most divergent boundaries are located below oceans. This is a cross-section of a divergent boundary, located below the Atlantic Ocean. Scientists have discovered that as the plates move apart, hot liquid rock, called magma, rises from the earth's mantle. The magma rises because it is lighter than the surrounding material. Magma is the name we give lava before it erupts from volcanoes, as it is doing here; and just as this lava is doing, magma hardens into rock when it cools. As the magma rises and cools, it adds new crust to old, spreading the ocean floor. This area of rising magma is known as a mid-ocean ridge. 22 This shows where magma is surfacing between plate boundaries, creating a mid-ocean ridge that circles the earth. The ocean floor spreads in one direction on one side of the ridge, and in the opposite direction on the other. The mid-ocean ridge is where plate material is created. This is where plate material is destroyed; an area where two plates are colliding, a convergent boundary. This is a cross-section of a convergent boundary. In this example, the plate on the right is carrying an ocean basin and is moving in this direction. The plate on the left is carrying a continent and is moving in the opposite direction. The plate carrying the ocean basin is heavier and is diving beneath the plate carrying the continent. The leading edge of the diving plate is consumed back into the earth's mantle. When one plate dives beneath another, it is called subduction, and the area where it occurs is called a subduction zone. Subduction may resemble what is happening on this lava lake, as sections of hardened crust dive beneath other sections. The highlighted areas on this globe mark convergent boundaries. Subduction is occurring at most of them. These are the areas where plate material is destroyed. Here again are divergent boundaries, where plate material is being created. Again, most of them are beneath the oceans, creating a mid-ocean ridge that circles the planet. 23 The grinding of plates has been going on for so long that most of the earth's crust is filled with cracks, not unlike the way this rock is filled with cracks. Scientists refer to a crack in the earth's crust as a fault, and it is in these faults that earthquakes originate. One side of the fault tries to move in one direction. The other side of the fault tries to move in a different direction, but the two sides are locked in place. They can't move until enough stress builds up to move them. If you were to bend a stick slowly, you would find that it won't break until sufficient stress builds up. That's what happens deep underground, the fault will remain locked until enough stress builds up, and then it will suddenly release, one side of the fault sliding past the other with a tremendous burst of energy. The energy that is released is in the form of seismic waves which radiate, or move outward. If the disturbance is big enough, the waves will eventually reach the surface, where they can cause considerable movement referred to as an earthquake. The place where a fault slips is called the earthquake's focus. The point on the earth's surface directly above the focus is called the earthquake's epicenter. What's interesting about earthquakes is how most of them coincide with plate boundaries. 24 These dots mark the locations of recent worldwide earthquakes. These lines mark plate boundaries. You can easily see how most earthquakes occur along plate boundaries. They occur near divergent boundaries, convergent boundaries, and they occur near the third type of boundary, a transform boundary. This is where two plates slide past each other. The world's most famous transform boundary is located in California. It splits the state into two sections. Here, the plate on the left is being driven in this direction. The plate on the right is being driven in the opposite direction. The two plates will remain locked until sufficient tension builds up between them, and then they will release in a sudden jerk, causing an earthquake. The amount of movement might only be a few inches, but could be several feet. The giant fault that is created by this plate movement is called the San Andreas fault. In some places the fault is clearly visible on the earth's surface, appearing as a nasty scar in the landscape. The San Andreas is over 500 miles long and slices its way past several major cities. It is among the most active faults in the world and one of the most dangerous. Scientists predict that a major earthquake will strike here in the near future. That's why they want to learn as much as they can about earthquakes. 25 This man isn't going for a hike. He's in the mountains to install earthquake monitoring equipment. This device is called a seismometer. It detects movement in the ground and sends out electronic tones. The tones may not sound like much to you or me, but they do to computers which can decipher the tones into meaningful information. Hundreds of seismometers have been buried as part of an earthquake-monitoring network. The seismometers are connected to a central computer miles away. Here, the tones are analyzed, and provide scientists with important information about surface movement in their area. The symbols on this computer monitor represent the locations of buried seismometers. The thin lines represent faults. When an earthquake occurs, scientists are able to pinpoint its exact location. Computers also help scientists analyze the different types of seismic waves that occur during an earthquake. The first waves that reach the surface are called P waves. P waves compress and stretch the material they travel through shown here in this model. This can be more easily seen using a model with a grid pattern. Here you can see that some sections of the grid have been stretched and other sections have been squeezed together. 26 The next waves that reach the surface are called S waves. S waves produce an up and down rolling motion in the earth's surface. There are other types of waves as well, and a single large earthquake can produce all of them. By examining various wave patterns, scientists can determine the strength of an earthquake, which is referred to as its magnitude. Earthquakes are assigned a number according to magnitude. The numbering system is referred to as the Richter scale. The larger the number, the greater the earthquake's magnitude. The Loma Prieta Earthquake of 1989 registered 7.1 on the Richter scale. Even though the epicenter was 60 miles away, damage in San Francisco and Oakland was considerable. Had the epicenter been closer, the damage to these cities could've been much worse, and thousands of people might've been killed. The closer large populations are to an earthquake's epicenter, the greater likelihood there will be for death and destruction. A quake not much larger than the Loma Prieta quake struck China in 1976. The epicenter, though, was near a highly populated area and as many as 650,000 people were killed. The most devastating earthquake to strike the United States was the San Francisco earthquake of 1906. Nearly 700 people were killed and the city center was destroyed. Scientists believe another devastating earthquake could strike a major city like San Francisco or Los Angeles in the very near future; a quake so large, it would have the potential of killing thousands. 27 That's why some cities conduct readiness alerts that simulate the kind of devastation that could occur, with the hope of being better prepared. That's why scientists study the damage caused by earthquakes. In this way, they learn more about the destructive capabilities of earthquakes and what can be done to avoid such destruction in the future. Scientists hope that one day they will be able to forecast earthquakes in much the same way they can forecast weather. So far, earthquake forecasting is not very precise and people living in earthquake prone areas are advised to expect an earthquake at any time. The next major earthquake might not strike for years, or it might strike within seconds. In this program, we have seen how most earthquakes are triggered by movements in the giant plates that form a shell around the earth, and that most earthquakes occur directly above the edges of these moving plates. Earthquakes can occur near divergent boundaries, convergent boundaries, and transform boundaries. We've seen that earthquakes occur when one side of a fault suddenly slides past another. The energy that is released is in the form of seismic waves which radiate in all directions. When these waves reach the surface, they can cause considerable surface movement and destruction. The place where a fault slips is called the earthquake's focus, and the earth's surface directly above the focus is called the epicenter. We've seen that the first wave to reach the surface is called a P wave, and the second wave is called an S wave. 28 We've seen that scientists use instruments like seismometers to record and measure these waves, helping them determine when and where an earthquake occurred and how powerful it was. The strength of an earthquake is referred to as its magnitude. Earthquake magnitudes are measured according to the Richter scale. We've seen the results of devastating earthquakes around the world and learned that an earthquake's destructive capability is greater near the epicenter. While earthquakes are frightening, they serve to remind us that our planet is in a constant state of change. While we may someday be able to forecast the occurrence of earthquakes, we will never be able to alter the great forces that are at work within our planet. 29 CLOZE EVALUATION QUESTIONS EARTHQUAKES: OUR RESTLESS PLANET NAME ________ DIRECTIONS: Select the answer, from the four choices given, by circling the correct letter. 1. Our earth is an ever-changing place on which we live. Some sources of this change are _______ . When one of these events happens, the effects can be slight or very damaging, depending upon the force of it. 1. A. geysers B. earthquakes C. hurricanes D. volcanoes 2. In order to understand how earthquakes occur, it is necessary to look inside the earth. The earth is made up of several different layers. The center layer is called the inner core. Next is the outer core, followed by the ________ , which is not as hot as these cores. 2. A. mantle B. crust C. magma core D. middle core 3. The uppermost layer of the earth is the region we live on. The _______ is this layer which is affected by what is happening beneath it. When earthquakes take place, the effect can cause great damage to buildings and property as well as injury and death to people. 3. A. surface B. mantle C. crust D. outside core 4. The crust would look quite different if we could strip away the oceans and plant life. In many places the crust is cracked. These large pieces of the crust are called _______ . The continents rest upon these pieces and have actual ly moved over millions of years. 4. A. plates B. landforms C. land masses D. countries 5. The earth's huge plates have been moving very, very slowly. The move ment is so slight that one cannot see it happening. Scientists believe that this process of movement, called _______ , is a major cause of geological 5. A. transformation B. subduction C. volcanism D. continental drift changes on the planet. 6. We need to look below the surface to understand the causes of earth quakes. Scientists believe that liquid matter in the mantle is circulating, or mov ing. This causes the earth's plates to move. When plates move in opposite directions, the spaces between them are called ________. Most of these are located beneath the oceans. 6. A. convergent boundaries B. divergent boundaries C. transform boundaries D. fault lines 7. The grinding of the earth's plates has been going on for millions of years. One result of this process is a crack in the earth's surface, called a ________ . One side of this crack tries to move in one direction while the other side moves in the opposite direction. The earth's plates remain locked in position until stress from below forces them to move. 7. A. fault B. break C. space D. separation 8. An earthquake occurs when the stress below the surface causes areas on both sides of the fault line to move. When this happens, the energy released is in the form of _______ . If the disturbance is big enough, the force will even tually cause damage to the surrounding areas. 8. A. mantle waves B. rock waves C. seismic waves D. tidal waves 9. In the state of California there have been a number of earthquakes. The most active earthquake area is along the _______ fault line. This fault line is over 500 miles long and it is one of the most active and dangerous earthquake zones on earth. 9. A. LaJolla B. San Jacinto C. San Jose D. San Andreas 10. Scientists record and study the movements of the earth's crust on a daily basis. Earthquakes can be classified according to the ________ which mea sures the intensity of the quake. A slight movement may register a 1 while an earthquake in China in 1989 measured a 7.1 on the scale. Perhaps someday scientists will be able to predict earthquakes with a high degree of accuracy. 10. A. Roenthen Scale B. Richter Scale C. Ranking Scale D. Rigidity Scale This form may be reproduced without permission from Rainbow Educational Media.