Focus point where earthquake rupture occurs


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Focus point where earthquake rupture occurs

    • Focus point where earthquake rupture occurs
      • Shallow focus -70 km or less (80% or more)
      • Deep focus -down to 700 km; often along subduction zones
    • Epicenter point projected onto the surface from the center of the Earth through the focus


Body waves -travel within the Earth

  • Body waves -travel within the Earth

    • Primary or P-waves
      • Compression
      • Faster of the two types (5.5-1.5 km/sec)
      • Passes through solids, liquids, or gases (sound at 15 Hz)
    • Secondary or S-waves
      • Shear waves
      • Travels only in solids
      • Velocity ~60% of P-wave velocity




Earthquake Magnitude (1935)

  • Earthquake Magnitude (1935)

    • Richter Magnitude (MW)
      • Measures of energy released (30 X increase/ magnitude)
      • Maximum amplitude 100 km from the epicenter
      • Logarithmic scale; a 10-fold increase per cm of amplitude
      • mb = log10(A/T) + Q(D,h)
      • MS = log10 (A/T) + 1.66 log10 (D) + 3.30
      • Seismograph
        • S-and P-waves
          • Magnitude (wave amplitude)
          • Distance (P-S)


1.0 30 pounds Large Blast at a Construction Site

  • 1.0 30 pounds Large Blast at a Construction Site

  • 2.0 1 ton Large Quarry or Mine Blast

  • 4.0 1,000 tons Small Nuclear Weapon

  • 4.5 5,100 tons Average Tornado (total energy)

  • 6.0 1 million tons Double Spring Flat, NV Quake, 1994

  • 6.5 5 million tons Northridge, CA Quake, 1994

  • 7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon

  • 7.5 160 million tons Landers, CA Quake, 1992

  • 8.0 1 billion tons San Francisco, CA Quake, 1906

  • 8.5 5 billion tons Anchorage, AK Quake, 1964

  • 9.0 32 billion tons Chilean Quake, 1960

  • 10.0 1 trillion tons San-Andreas type fault circling Earth

  • 12.0 160 trillion tons Fault Earth in half through center, OR

  • Earth's daily receipt of solar energy



Moment method

  • Moment method

    • Essentially the same as Richter at higher magnitudes
    • May be applicable over a wider range of ground motions than Richter








Earthquake Intensity

  • Earthquake Intensity

  • Varies with distance from the epicenter (unlike Richter or Moment scales)

    • Radio wave model




Rate of change in horizontal and vertical velocity

  • Rate of change in horizontal and vertical velocity

  • Measure with respect to gravity (1 g = 9.8 m/s2)

  • Building resistance varies with construction (adobe vs.concrete)



Regional Changes in Land Elevation

  • Regional Changes in Land Elevation

    • 1964 Alaskan Quake
    • 1992 Mendocino, CA
  • Long and short term prediction

  • Estimation of Seismic Risk (maps)

  • Conditional Probabilities of Future Earthquakes

    • Probability maps
      • The Loma Prieta quake as probable before 1989
      • Failed at San Bernardino in 1992




Basically aseismic (i.e., little activity) since Paleozoic

  • Basically aseismic (i.e., little activity) since Paleozoic

  • Only about 6 "real" earthquakes (until 2006!)

    • 1879-location unknown; felt in Fla. and Ga.
    • 1893-Jacksonville
    • 1933-Palatka
    • 1945-offshore Miami
    • 1973-Merritt Island
    • 1975-Daytona Beach (most recent)
  • 1998 Panhandle (Jay fault; epicenter near Brewton,Alabama; MR = 4.5)






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