Fault formationWhen rocks undergo large amounts of pressure,the rock may break.When rocks break, they move along surfacescalled faults.
What causes faults? Plates moving put stress on rocks near plateedges, causing rocks to bend compress, stretch, or break.Earthquakes are the vibrations produced by the breaking of rock.
How earthquakes occur Rocks move past each other at faults Rough surfaces catch Movement of fault is stopped Forces keep driving rocks to move This stress causes rocks to break, move along, fault, and return to original shape Earthquake occurs.Range from unnoticeable to devastating
3 types of faultsNormalReverse (Thrust)Strike-Slip
Normal fault Tension causes rocks to be pulled apartRock above the fault surface moves downwardANIMATION:http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Normal+Fault&flash_file=normalfault&flash_width=220&flash_height=320
Reverse faults Compression forces squeeze rocksRock above reverse fault surface forced up and over rock below fault surfaceANIMATION:http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Thrust+Fault+and+Reverse+Fault&flash_file=thrustfault&flash_width=220&flash_height=320
Strike slip faultRocks are moving past each other without much upward and downward movement-called shear Ex: San Andreas FaultANIMATION:http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=S
Seismic WavesWaves generated by an earthquake that travel through the earth Focus (foci if plural): point where energy release first occurs 3 types: Primary waves Secondary waves Surface waves
Primary wavesP-waves Particles move back and forth in the direction that the wave is travelling Like waves through a spring
Secondary wavesSecondary waves (s waves) Particles move at right angles to the direction of wave travel (up and down)
Surface wavesSurface waves Particles move in a backward, rolling motion and side to side in a swaying motion Cause buildings to fall
Locating an EpicenterDifferent seismic waves travel at different speeds:Primary are fastest, then secondary, finally surfaceScientists use the different speeds to determine distance to the epicenter
Measuring Seismic WavesSeismograph: measures the time seismic waves arrive
Seismograph StationsSeismographs are located all over the US and worldIf waves reach three or more stations, the epicenter can be determinedDraw a circle around each station-the radius of each circle equals stations distance from epicenterPoint where circles meet is epicenter
Bibliography Images"2010 Haiti Earthquake." Wikipedia. Wikimedia Foundation, 26 June 2012. Web. 29 June2012. <http://en.wikipedia.org/wiki/2010_Haiti_earthquake>."Earthquake Glossary." Earthquake Glossary. USGS, 2009. Web. 29 June 2012.<http://earthquake.usgs.gov/learn/glossary/>."Fault (geology)." Wikipedia. Wikimedia Foundation, 29 June 2012. Web. 29 June 2012.<http://en.wikipedia.org/wiki/Fault_(geology)>. InformationNational Geographic Society, Ralph M. Feather, Susan L. Snyder, and Dinah Zike. EarthScience. N.p.: Glencoe, 2002. Print.