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Seismic Waves and Seismographs

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Physics of Waves

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Wave Simulations Colorado School of Mines Tutorial Colorado School of Mines Tutorial Wave Basics

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LL F L F = k * L/L (Hooke’s Law) k = Young’s modulus Stress = F/A = K u/ x= Strain Rand quartzite strain Elastic Materials

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Elastic Waves Force = Mass x Acceleration (Newton rules!) u u+ du x x + dx A F(x) F (x+dx) Net force = F(x+dx) – F(x) = F = [ *Area*dx] *acceleration F/ x = * acceleration * Area] but F = Stress/Area = K * u/ x (Hookes law) so K * u/ x x = K u 2 / x 2 = * u 2 / t 2 i.e. a wave equation where V= (k ) 1/2

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Seismic Wave Equation d 2 u/dx 2 = ( /k) du 2 /dt 2 which has solutions of the form U(x,t) = A e -i(kx- t) + Be -i(k+ t)

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Seismic Waves http://www.uwgb.edu/dutchs/EarthSC202Notes/quakes.htm

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Seismic Waves Body Surface P S Love Rayleigh

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Surface (Rayleigh) Waves

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Seismic Wave Speeds MaterialP wave Velocity (m/s)S wave Velocity (m/s) Air332 Water1400-1500 Petroleum1300-1400 Steel61003500 Concrete36002000 Granite5500-59002800-3000 Basalt64003200 Sandstone1400-4300700-2800 Limestone5900-61002800-3000 Sand (Unsaturated)200-100080-400 Sand (Saturated)800-2200320-880 Clay1000-2500400-1000 Glacial Till (Saturated)1500-2500600-1000

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P vs S

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Seismometry earthquake.usgs.gov/4kids/games/ coloring/seismograph.gif www.gpc.peachnet.edu/~pgore/ geology/geo101/quakelec.htm

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Pendulum Seismograph www.psd.wednet.edu/jrsrhigh/ science/seismograph.GIF T= 2 L/g For T= 1 sec, L =.2 m T= 20 sec, L = 99 m

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Seismograph Response http://www.uwgb.edu/dutchs/EarthSC202Notes/quakes.htm

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Seismograph Response Curve www.geophys.uni-stuttgart.de/.../ man_html/node10.html

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Dispersion Kanamori and Abe (1968) Fig. 2.8-4 Stein and Wysession (2003) Oliver (1962) Love Waves

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Vertical Seismograph Bolt, 1993

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Horizontal Seismograph (Swinging gate) library.thinkquest.org/ 15616/aard4n.html

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Seismic Station

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Seismic Pier Remote Display

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Seismometer/graph Menagerie

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