Earth Science 8.2 Measuring Earthquakes Measuring Earthquakes.
Earthquakes
description
Transcript of Earthquakes
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EQ = Movement of E’s lithosphere that occurs when rocks in the lithosphere suddenly shift, releasing stored energy.
EQs occur b/c stress forces of have exceeded the strength of rock.
Stress builds when rocks along 2 sides of a fault snag and lock (friction) as stress builds – so does POTENTIAL ENERGY IN ROCKS
When rocks are strained beyond limit – they break & move. (Potential Kinetic Energy in form of seismic waves)
EQs
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Stress & Strain on Rocks
Stress – Force that squeezes rocks together, pulls them apart, pushes in diff. directions.
Stress causes strain or deformation (change in shape or volume) of rock
Stress
Folds Faults
Does not exceed rock strength
Exceeds rock strength
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Stress
Folds = Bending rock layers
Faults = Breaks in rock layers & movement along breaks
Does not exceed rock strength
Exceeds rock strength
High Temps. & Pressure
Low Temp. & Pressure – Near Crust
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Folds
Anticline = up facing foldSyncline = down ward facing fold
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Faults
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Types of Faults
http://www.windows.ucar.edu/tour/link=/earth/geology/fault.html
1. Dip – SlipMotion up or down fault surface
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Types of Faults
2. Strike – slip
Sliding – Horizontal Movement
3. Oblique – slipdip-slip & strike slip combined
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Interpretation of Tectonic History
Divergent Transform
Plate Boundary:
Convergent
NormalThrust/Reverse Strike-Slip
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•EQ vibrations begin at a point called a FOCUS.
•Vibrations travel from focus through the earth’s crust as waves.
•Surface directly above the focus is called the epicenter.
•These waves can be detected and measured on earth’s surface with a SEISMOGRAPH.
EQ Vibrations
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Instrument that measures & records EQ waves. Strength of EQ waves is referred to as MAGNITUDE.
SEISMOGRAPHS
Wave Motion: http://sunshine.chpc.utah.edu/labs/seismic/index.htm?ASPIRE_Session=964f1ed30b7e49ceb81bd77f444d9230
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3 Types of Seismic Waves1. Primary Waves (P waves)
2. Secondary Waves (S waves)
3.Surface Waves
Each wave originates from the FOCUS of the earthquake.
Each wave travels in a different way, at different speeds, and causes different amounts of destruction.
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Seismic Waves = vibrations produced by energy released during EQ
Virtual EQs http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html
Seismic Waves http://www.geo.mtu.edu/UPSeis/waves.html
P Waves: Primary Wave
•Arrives 1st & Travels FASTER.
•Compress & Expand like accordion (like sound waves)
•Move through Solids & Liquids
•Least destructive
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Seismic Waves S Waves – Secondary
• What you FEEL in an EQ
• Rock moves up & down or side to side (Snake-like)
• Arrive after P
• Move only through SOLIDS
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Seismic Waves: Surface Waves
• Surface Waves develop when vibrations reach surface
• Slowest waves• Most destructive, most damaging
• More P & S wave animations: http://www-rohan.sdsu.edu/~rmellors/lab8/l8maineq.htm
• Video clip: http://news.bbc.co.uk/1/hi/sci/tech/4126809.stm
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Rating Earthquakes
Earthquakes are rated in terms of MAGNITUDE or INTENSITY by different scales.
1.Moment Magnitude Scale
2.Richter Scale
3.Mercalli Scale
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• Uses a seismogram
• Rates on scale from 1- 10
• Looks at Eqs in terms of ENERGY
• Each # releases 31 times more ENERGY than the # before it.
Example A 6 releases 31 times more energy than a 5, and a 5 releases 31
times more energy than a 4. The energy difference between a 4 and a 6 EQ is 31 X 31 = 961
Moment Magnitude Scale
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• Uses a seismogram
• Rates on scale from 1- 10
• Looks at Eqs in terms of the SIZE OF THE WAVES
• Each # has waves 10x bigger than previous #1 – 3: Small earthquake waves – very little shaking
4 – 6: Moderate earthquakes – noticeable shaking and some damage
7 - 10+ BIG Earthquakes – Very destructive
Richter Scale
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Mercali Intensity Scale
•Measures observed RESULTS or DAMAGE of Earthquake on a 1 – 12 scale
•Degree of shaking and DAMAGE to structures
•Don’t need a seismogramLink
•http://www.abag.ca.gov/bayarea/eqmaps/doc/mmi.html
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•Deaths & Injuries
•Damage to buildings & structures
•Underground water and gas pipes break – floods & fires
•Landslides
•Tsunamis
EFFECTS OF EQs
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Seismic Waves are used to Study Earth’s Interior
Link: http://sunshine.chpc.utah.edu/labs/seismic/index.htm?ASPIRE_Session=964f1ed30b7e49ceb81bd77f444d9230
P and S waves are “bent” and their velocities are affected as they move through material of varying density
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Latest Quakes
http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/quakes_all.php
Top Ten Lists
http://earthquake.usgs.gov/eqcenter/top10.php
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LinksVirtual Earthquakeshttp://www.sciencecourseware.org/VirtualEarthquake/
VQuakeExecute.htmlWave Types http://www.geo.mtu.edu/UPSeis/waves.htmlTriangulation & “Hearing EQs”http://www.seismo.unr.edu/ftp/pub/louie/class/100/seismic-waves.htmlMore virtual seismogramshttp://www-rohan.sdsu.edu/~rmellors/lab8/l8maineq.htmEarthquakes outline subducting slab – Interactive Web Labhttp://openlearn.open.ac.uk/mod/resource/view.php?id=172185
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