Ch06_Outline - Chapter 6 Restless Earth Earthquakes...

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 Chapter 6  Restless Earth:  Earthquakes, Geologic  Structures, and  Mountain Building
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        What Is an Earthquake? An  earthquake  is the vibration of  Earth produced by the rapid release  of energy Energy released radiates in all  directions from its source, the  focus   Energy is in the form of waves  Sensitive instruments around the  world record the event 
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    Earthquake Focus  and Epicenter Figure 6.2
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        What Is an Earthquake? Earthquakes and faults  Movements that produce earthquakes  are usually associated with large  fractures in Earth’s crust called  faults Most of the motion along faults can  be explained by the plate tectonics  theory  
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        What Is an Earthquake? Elastic rebound Mechanism for earthquakes was first  explained by H. F. Reid  Rocks on both sides of an existing fault  are deformed by tectonic forces  Rocks bend and store elastic energy  Frictional resistance holding the rocks  together is overcome   
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    What Is an Earthquake? Elastic rebound Earthquake mechanism Slippage at the weakest point (the focus)  occurs  Vibrations (earthquakes) occur as the  deformed rock “springs back” to its  original shape  (elastic rebound)
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    What Is an Earthquake? Foreshocks and aftershocks Adjustments that follow a major  earthquake often generate smaller  earthquakes called  aftershocks   Small earthquakes, called  foreshocks,   often precede a major earthquake by  days or, in some cases, by as much  as several years  
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    Seismology The study of earthquake waves,  seismology,  dates back almost 2000  years to the Chinese  Seismographs,  instruments that  record seismic waves  Record the movement of Earth in  relation to a stationary mass on a  rotating drum or magnetic tape 
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    Seismology Seismographs More than one type of seismograph is  needed to record both vertical and  horizontal ground motion  Records obtained are called  seismograms   Types of seismic waves  Surface waves Travel along outer part of Earth 
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    Seismology Types of seismic waves   Surface waves Complex motion  Cause greatest destruction  Exhibit greatest amplitude and slowest  velocity
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    Seismology Types of seismic waves Body waves Travel through Earth’s interior  Two types based on mode of travel  Primary (P) waves   Push-pull (compress and expand)  motion, changing the volume of the  intervening material  Travel through solids, liquids, and  gases
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  Seismology Types of seismic waves Body waves Secondary (S) waves “Shake” motion at right angles to 
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This note was uploaded on 03/21/2012 for the course GEO 1013 taught by Professor Hefner during the Fall '07 term at The University of Texas at San Antonio- San Antonio.

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Ch06_Outline - Chapter 6 Restless Earth Earthquakes...

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