what are earthquakes?
DESCRIPTION
What are earthquakes?. Earthquakes occur mainly at plate boundaries. http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_quakes_volcanoes_plates.gif. Pressure. Pressure builds up as plates move. Eventually rocks break at a fault . Energy is released as seismic waves . (3 kinds). - PowerPoint PPT PresentationTRANSCRIPT
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What are earthquakes?
• Earthquakes occur mainly at plate boundariesplate boundaries.
http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_quakes_volcanoes_plates.gif
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Pressure
• Pressure builds up as plates move.
• Eventually rocks break at a faultfault.
• Energy is released as seismic seismic waveswaves. (3 kinds)
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Types of Forces and Faults
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Normal Faults
Tension – pulling rocks apart
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Reverse Faults
Compression– pushing rocks together
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Strike-Slip Faults
• Caused by shearing
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Describing the location
Earthquakes occur underground. The spot underground where the rock breaks
is the focusfocus. The spot on the surface directly above that is
the epicenterepicenter.
http://www.harcourtschool.com/scienceglossary/images/gr4/epicenter4.jpg
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Types of Waves
Primary WavesPrimary Waves (first) – longitudinal waves that travel the fastest- originate at the focus
These are the first sign of an earthquake
http://astro.uchicago.edu/cara/outreach/se/ysi/1999/intro2.html
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Secondary Waves
Transverse Waves that start out at the focus
http://astro.uchicago.edu/cara/outreach/se/ysi/1999/intro2.html
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Surface Waves
Originate at the epicenter (on the surface)
Cause the most destruction
http://www.gly.fsu.edu/~salters/GLY1000/Chapter4/Slide18.jpg
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How far away?
• The lag time between the primary and secondary waves is used to determine how far away the earthquake occurred
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Measuring an Earthquake
SeismometersSeismometers – instruments used to sense and record earthquake data
http://www.thetech.org/exhibits/online/quakes/seismo/
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Measuring an Earthquake
SeismographsSeismographs – recordings of seismic waves produced by seismometers
http://www.thetech.org/exhibits/online/quakes/seismo/
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http://www.inel.gov/env-energyscience/seismic/network.shtml
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Amplitude
• The height of a wave
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Locating the epicenter
3 Seismograph stations are required to triangulate the location
http://www.tecedu.com/about/images/us-map.gif
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Richter ScaleMeasures the magnitude of earthquakes
using the distance from the epicenter and the amplitude of the largest wave.
http://www.wanadoo.jo/medias/img/SGE.GXY52.050904182653.photo00.default-245x208.jpg
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Determining Richter scale
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Richter ScaleEach number increase on the Richter
scale indicates an increase of
10x’s in amplitude
32 x’s more energy
http://www.wanadoo.jo/medias/img/SGE.GXY52.050904182653.photo00.default-245x208.jpg
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Historic Earthquakes
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Alaska 1964, 9.2
http://epod.usra.edu/archive/images/augustanack3.jpghttp://earth.geol.ksu.edu/sgao/g100/plots/1031_earthquake_trig.jpg
http://www.tfhrc.gov/pubrds/03nov/images/mccarthy2.jpg
http://www.tfhrc.gov/pubrds/03nov/05.htmhttp://www.disasterrelief.org/Disasters/010326alaskaquake1964/Images/rail.gif
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Modified Mercalli Scale
Measures intensity or damage caused by an earthquake
I -XII
http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf
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Moment magnitude scale
Used to record energy released by an earthquake and takes into account the size of the fault rupture.
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Tsunamis
• are large fast moving waves that are produced by moving crust under the ocean
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Recent Tsunami’s
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