35 - Big Earthquakes release more low-frequency energy Wave...

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October 21, 2010 Why are  shear  waves the  biggest wave phase  for local events, but  surface  waves are biggest waves for distant events? 1. Body waves spread as a sphere (4   r 2  = surface area   so energy spreads  as 1/r 2 ) 2. Surface waves spread as a cylinder (2  x r x t = surface area) so the energy   spreads as 1/r = So Body waves lose energy faster as r (distant) increases (because of that  exponent)  When the EQ happens, the biggest wave phase that emanates from most EQs is  usually the shear waves, but they die off really fast.  3. Body waves lose energy faster because they have shorter periods/high  frequency than surface waves Earth attenuates high frequency waves faster than low-frequency waves
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Unformatted text preview: Big Earthquakes release more low-frequency energy Wave lose energy on every cycle, so the shorter the wavelength, the faster it dies out. How do you tell the difference between and earthquake and an explosion (nuclear weapon underground)? Answer: How we monitor nuclear weapons tests - seismology Explosion: Releasing compression (huge p-waves) Eqs: generate lots of shear waves DIAGRAM 4 1 st motion focal mechanism, only based on motion of station caused by 1 st arriving p-wave-LIKE LAB ON 10/19 -Were interested in the fastest wave to get to the station -The stations that are farther away, you are actually plotting the point 20:34 20:34 20:34...
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This note was uploaded on 10/26/2010 for the course GEOL 240Lxg at USC.

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35 - Big Earthquakes release more low-frequency energy Wave...

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