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Size of earthquakes

Size of earthquakes. MODIFIED MERCALLI SCALE Defines the INTENSITY of an earthquake by the amount of damage caused. Characteristics:. Depends on subjective assessment of the damage and not any measurement with an instrument

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Size of earthquakes

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  1. Size of earthquakes

  2. MODIFIED MERCALLI SCALE • Defines the INTENSITY of an earthquake by the amount of damage caused

  3. Characteristics: • Depends on subjective assessment of the damage and not any measurement with an instrument • Does not provide an accurate measurement of the strength of the earthquake (Why?) • Useful for planners and building officials

  4. RICHTER MAGNITUDE SCALESpecifies the amplitude of the largest ground motion generated by the earthquake at a seismograph station located 100 km from the epicenter

  5. Characteristics of Richter Scale • The amplitude can be measured directly from a seismogram (more quantitative) • The scale is logarithmic • An increase of one magnitude on the Richter scale means approximately 30- fold increase in energy released

  6. MOMENT MAGNITUDE SCALEProvides more accurate measure of the total energy released during earthquakes than the Richter scale. Seismic moment = (amount of slip) x (the area of rupture) x (rock strength)

  7. Bigger earthquakes: • Cause more slip • Break more rocks (bigger rupture area) • Happen in stronger rocks (why?)

  8. Locating earthquake epicenters

  9. or HYPOCENTER

  10. Arrival time Arrival time 5 10 15 20 25 30 35 40 45 50 55 60 Time (Minutes) The instant an earthquake wave appears on the seismogram is called the ARRIVAL TIME of the wave

  11. P- wave arrival time S- wave arrival time Use TRAVEL – TIME CURVE Distance between the earthquake epicenter and the recording station

  12. The P- and S- wave arrival time difference from at least three different seismographs can be used to locate the epicenter of an earthquake More on that during lab this week

  13. City of Salinas, after the October 17, 1989, Loma Prieta Earthquake Surface Waves and Effects of Earthquakes http://pubs.usgs.gov/dds/dds-29/web_pages/salinas.html

  14. Surface waves Travel along the surface of the earth There are two broad groups of seismic waves Body waves Can travel through the interior of the earth

  15. SURFACE WAVES • Not much used in studying the interior of the earth • Slower than body waves • Most destructive of the earthquake waves

  16. Two types of surface waves Rayleigh waves (“vertical” surface waves) Love waves (“horizontal” surface waves)

  17. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm • Rayleigh waves • Make the surface go up and down like ripples

  18. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm • Love waves • Make the ground move sideways like a moving snake

  19. Effects of earthquakes • Ground shakes, buildings collapse, structural damage, death and destruction… • Fire • Landslides • Tsunamis (do NOT call them tidal waves)

  20. 2004 Indonesian tsunami, http://staff.aist.go.jp/kenji.satake/animation.html

  21. Tsunami generation

  22. Earthquake prediction • Monitoring faults for small tremors and foreshocks • Radon emissions • Measuring ground tilts • Animal behavior • Studying historic earthquake patterns

  23. http://www.usgs.gov/hazards/images/maps/earthquake_lores.jpg

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