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Name of School Date Earthquakes and Seismology
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Plate Tectonics
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A Century of Earthquakes: 1906-2006
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Global Seismographic Network
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2006 Earthquakes > M5.5 2006 Earthquakes > M5.5 in the world
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How Many? Earthquake Magnitude and Equivalent Energy Comparisons Source: http://www.iris.edu/edu/onepagers/no3.pdf
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Earthquakes generate Seismic Waves that travel around the globe and tell us about the Earth’s interior.
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Simple Seismometer A simple way to measure shaking from earthquakes. To see it in action, watch this 14 sec video http://www.youtube.com/watch?v=DX5VXG mdnAg&NR=1
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What is an Earthquake? Earthquake: The sudden release of elastic energy by fracture over some area of the earth.
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What is an Earthquake? Earthquake: The sudden release of elastic energy by fracture over some area of the earth. Earthquake: The sudden slip on a fault (release of elastic energy), and the resulting ground shaking and radiated seismic energy caused by the slip.
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Fault: A fracture (crack) in the earth, where the two sides move past each other and the relative motion is parallel to the fracture.
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Typical Plate Boundaries
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Plate Boundaries & earthquakes
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Types of Faults
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A fence built over a fault…
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1906 San Francisco Earthquake Fence Offset
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Offset Stream Channels in Central California
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Types of Seismic Waves P-wave: Primary Wave. Compressional wave, like a Slinky © being pushed and pulled. S-wave: Secondary Wave. This is a shear wave where particles move perpendicular to the travel direction of the wave. Surface Waves: Both Love and Rayleigh Waves. Only shallow particles are disturbed. Love waves are sideways, Rayleigh are vertical (like ocean waves).
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Types of Seismic Waves
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Seismographs HorizontalVertical
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Distance to quake epicenter P S L Note: P-wave first S-wave second Surface waves last Time lag between p and s- wave arrival is called t. Fig 3.22
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Ts=23s Tp=14s Maximum Amplitude = 540 mm
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Locating Earthquakes Fig. 3.23
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Locating Earthquakes
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Earthquake Size Richter Magnitude: Relative Size of an Earthquake (based on seismograph shaking) Seismic Moment/Moment Magnitude: Absolute Size of an Earthquake (based on energy released) Modified Mercalli Intensity: How much I’m shakin’ (based on talking to people)
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Calculating Richter Magnitude A.K.A Local Magnitude M L = log 10 A - log 10 A o A is the amplitude of the s-wave measured at given station A o is the amplitude of a M R =0 event at the same distance P S
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Log of the Amplitude for a Magnitude 0 Earthquake
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M = 4 M = 0
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Earthquake: The sudden slip on a fault (release of elastic energy), and the resulting ground shaking and radiated seismic energy caused by the slip.
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Aki ’ s Seismic Moment Formula M o = s A Where: is the shear modulus. S is the average slip on the faulted area. A is the area of the fault plane over which slip has occurred. Shear modulus ( can just be thought of as the strength of the faulted material
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Modified Mercalli Intensity Based on response of humans and structures I (not felt except by few) XII (total destruction) Still useful for comparison with older earthquakes for which there were no instrument records
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Earthquake Info on the Internet http://earthquakes.usgs.gov/
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Earthquake Info on the Internet http://earthquakes.usgs.gov/eqcenter/dyfi.php
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Did You Feel It??? Go online and tell us!
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Earthquake Info on the Internet http://www.data.scec.org/recenteqs.html
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Southern California with Faults & the Big Bend
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Southern California from Space(1)
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Southern California from Space With a Few Major Faults
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Historical Earthquakes (1800-1850) Historical Earthquakes (1850-1900)Historical Earthquakes (1900-1950) Historical Earthquakes (1950-2004) Historical Earthquakes (1000-1800) Smith and Sandwell, 2006
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Thank You for Your Attention Questions?
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