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Transcript
Features of Earthquakes Seismic Waves ________________________ waves, produced by _________________________________ are very similar to waves that you can produce by shaking a rope up and down. __________________________ waves travel through the ______________________________. During a strong earthquake the ground moves ______________________________ and backward, heaves up and down, and ________________________ from side to side. The ______________________________ of the ground can _____________________________ likes waves do in water. Origin of Seismic Waves The ______________________ that is produced when rocks stretch and break builds up and is _____________________________ when the elastic limit is reached. This __________________________ is in the form of _____________________________ waves. The point where this ____________________________ is first released is called the _______________________ of the earthquake. The foci of most ____________________________ are within 65 km of Earth’s __________________________. A few have been ______________________________ as deep as ____________________. ______________________________ waves are produced and travel outward from the __________________________ focus. Primary Waves When ______________________________ occur, three different types of _________________________ waves are produced. All of the waves are ___________________________ at the same time, but each behaves differently within ________________. 1 Primary waves cause __________________________ in rocks to move back and forth in the __________________________ direction that the waves is traveling. Secondary and Surface Waves ____________________________ waves move through Earth by causing ______________________________ in rocks to move at right angles to the direction of wave travel. ____________________________ waves cause most of the destruction resulting from _________________________. Surface waves move rock particles in a ________________________________, rolling motion and a sideto-side _________________________ motion. Many buildings are unable to ________________________ intense shaking because they are made with _______________________ materials. The buildings fall apart when ________________________ waves cause different parts of the building to move in different directions. Secondary and Surface Waves Cont. _____________________________ waves are produced when earthquake __________________________ reaches the surface of the Earth. _______________________________ waves travel outward from the ______________________________. The earthquake ________________________ is the point on Earth’s surface directly above the earthquake _______________________. Locating an Epicenter Different _______________________________ waves travel through Earth at different __________________________. ______________________________ waves are the fastest, secondary waves are ____________________________, and surface waves are the slowest. ______________________________ have learned how to use the different speeds of seismic waves to determine the distance to an _____________________________ epicenter. 2 When an __________________________ is far from a location, the primary wave has more time to put distance between it and the ___________________________ and surface waves. Measuring Seismic Waves _________________________ waves from earthquakes are measured with an instrument known as a __________________________________. ________________________________ register the _____________________________ and record the time each arrived. Seismographs consist of a ________________________ drum of paper and a ________________________ with an attached pen. When seismic waves reach the ________________________, the drum vibrates but the _____________________________ remains at rest. The ____________________________ pen traces a record of the vibrations on the moving __________________________ of paper. The _________________________ record of the seismic activity is called a ________________________. Seismograph Stations Each type of ______________________ wave reaches a seismograph station at a different _________________ based on its speed. ______________________ waves arrive ______________________ at the station, and _________________________ waves, which travel slower, arrive __________________________. Because ______________________________ waves are the slowest, they arrive ____________________________. The difference in __________________________ times is used to calculate the distance from the seismograph station to the _____________________________ epicenter. Seismograph Stations Cont. 3 Of ________________________ waves reach three or more seismograph stations, the location of the ___________________________ can be determined. To locate an __________________________, scientists draw _________________________ around each station on a map. The _________________________ of each circle equals that stations distance from the __________________________ epicenter. The point where all _____________________ circles intersect is the location of earthquake _______________________. Basic Structure of the Earth The ______________________ of the Earth is the core ad it is a solid, dense material, made mostly of ______________________ with small amounts of nickel, oxygen, silicon, and sulfur. _____________________________ from the layers above causes the inner core to be ________________________. Above the solid ________________________ core lies the liquid outer core, which is also made of mostly ______________________. Earth’s _________________________ is the largest, or _____________________________ layer, lying directly above the outer core. It is made mostly of _______________________, oxygen, magnesium, and _____________________. The mantle is often divided into an ________________________ part and a lower part based on changing _____________________________ waves speeds. A portion of the upper __________________________, called the ________________________________, consists of weak rock that con flow slowly. Earth’s Crust The ____________________________ layer of the Earth is the _____________________________. Together the ______________________ and a part of the upper mantle just beneath it make up the Earth’s __________________________________. 4 The ________________________ is broken into a number of plates that move over the ____________________________ beneath it. The ___________________ of Earth’s crust _________________. It is more than 60km thick in some __________________________ regions and less than 5km thick under some parts of the ________________________. Compared to the _________________________ the crust contains more silicon and aluminum and less _________________________ and iron. Earth’s ____________________________ is generally less ____________________________ than the mantle beneath it. Mapping Earth’s Internal Structure As you just learned, the ____________________________ and paths of seismic waves changes as they travel through materials with different _______________________. By studying __________________________ waves that have traveled through Earth, scientists have identified different ____________________________ with different densities. In general the _________________________ increase with depth as pressure ________________________. Studying ______________________________ waves has allowed scientists to map Earth’s _____________________________ structure without being there. Layer Boundaries _____________________________ waves speed up when they pass through the bottom of the ________________________ and enter the upper mantle. This __________________________ between the crust and the upper mantle is called the __________________________________ discontinuity or Moho. The mantle is _____________________________ into layers based on changes in seismic wave ________________________. For example, _____________________________ and secondary waves slow down again when they reach the _________________________________. 5 Then they generally speed up as they move through a more ____________________________ region of the mantle below the __________________________________. The ______________________ is divided into two layers based on how _________________________ waves travel through it. _____________________________ waves do not travel through the _____________________________ core. __________________________ waves slow down when they reach the outer core, but they speed up again upon reaching the ______________________________ inner core. 6