1/23/12 - bellringer ► how might you measure an earthquake?
TRANSCRIPT
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1/23/12 - Bellringer
►How might you measure an earthquake?
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19.3 – Measuring and Locating Earthquakes
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Magnitude
►Magnitude = a measure of energy produced by earthquake
►Amplitude = Height of wave►Richter Scale = numerical rating
system used to measure the magnitude of an earthquake
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Richter Scale
►Numbers are determined by amplitude of largest seismic wave
►Each successive number represent an increase in amplitude of a factor of 10
►Example: Magnitude-8 is 10x larger than magnitude-7 Energy difference is even greater, = 32x
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Richter scale
http://www.maelor-humanities.org.uk/GCSEhum/Resources/PP-photos/pp-KeyIss3/Richter.scale.jpg
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Moment Magnitude Scale
►Rating scale that measures the energy released by an earthquake taking into account the size of the fault rupture, the amount of movement, and the rock’s stillness
►Comparison with Richter: New Madrid, MO 1812 - Richter scale 8.7 -- MMS 8.1 San Francisco, CA 1906 - Richter scale 8.3 -- MMS 7.7 Prince William, AK 1964 - Richter scale 8.4 -- MMS 9.2 Northridge, CA 1994 - Richter scale 6.4 -- MMS 6.7
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Mercalli Scale
►Measures intensity of earthquake using Roman Numerals Worse damage = higher numeral
►Intensity = amount of damage caused by earthquake
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http://www.state.il.us/IEMA/images/Mercalli.jpg
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Intensity
►Depends on amplitude of surface waves
►Surface waves decrease in size with increase distance from focus Intensity decreases as well
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Depth of Focus
►Shallow, Intermediate, Deep►Shallow = catastrophic with high
intensity Produce greater maximum intensity than
deep focus►Deep = smaller vibrations
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Locating Earthquakes
►Seismogram and Travel-time Curve allow scientists to determine distance to epicenter
►Seismogram records time elapsed between arrival of waves
►Distance is determined by measuring separation of waves on seismogram and identifying the same separation on Travel-Time curve
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Locating Earthquakes Cont.
►Multiple seismograms are needed because one just determines certain distance in any direction Circle is drawn around station with radius
equal to distance►Adding data from other stations
narrows area of focus 2 circles overlap @ 2 points 3 circles overlap @ 1 point = EPICENTER
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Epicenter
http://wps.prenhall.com/wps/media/objects/3030/3102952/epicenter_tasa_shad.jpg
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Seismic Belts
►Majority of Earthquakes occur along seismic belts that separate large regions of little or no seismic activity
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►Most correspond closely with plate boundaries
►80% along Circum-Pacific Belt Subduction zone
http://upload.wikimedia.org/wikipedia/commons/thumb/0/09/Pacific_Ring_of_Fire.png/800px-Pacific_Ring_of_Fire.png
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In-Class Assignment
►Get out a new sheet of paper!
►Mini Lab pg. 541
►Ignore #1►Turn in Traced Map with labeled
intensities, contour lines, and analysis question answers at the end of class