Earthquake Measurement and Preparedness

Measuring an Earthquake

  • Early Developments
    • Earliest seismoscope from China (132 AD) by Zhang Heng
    • Could determine the direction of earthquakes up to hundreds of miles away.

Modern Seismometers

  • Components
    • Wire, Damping magnet, Weight, Rotating drum, Pen
    • Example of a simplified modern seismometer shown on Page 2.
  • Electromagnetic Seismometer
    • Uses a spring, magnet, electric coil, and measures ground movement.

Seismograph Examples

  • Example from Temple University recorded data from the 2011 Japan earthquake.

Earthquake Magnitude Scales

  • Three Major Methods to Measure Earthquakes:
    1. Richter Scale
    • First magnitude estimates recorded with seismometers.
    • Measures maximum ground shaking from S-wave.
    • Varies by distance and is specific to one location.
    1. Moment Magnitude
    • Measures absolute size and energy released from earthquakes.
    • Based on area of rupture, amount of slippage, and rock rigidity.
    • Estimations can take days to months.
    1. Modified Mercalli Intensity Scale
    • Qualitative scale (I-XII) based on damage and people's perceptions.
    • Variation in damage intensity can occur in regions from the same earthquake.
    • Damage maps based on surveys and reports show where impact is most severe.

Modified Mercalli Intensity Scale

  • Intensity Levels
    • I: Not felt
    • II: Felt by a few, especially on upper floors.
    • III: Noticeable indoors.
    • IV: Many outdoors may not feel it.
    • V: Felt by most, some broken dishes.
    • VI: Everyone feels it, slight damage.
    • VII: Many frightened, heavy furniture moved.
    • VIII: Considerable damage to ordinary structures.
    • IX: Great damage in substantial buildings.
    • X: Some masonry structures destroyed.
    • XI: Total destruction of buildings.
    • XII: Objects thrown into the air.

Effects of Earthquakes

  • Common Hazards:
    • Fires: Caused by ruptured gas lines or fuel tanks after quakes.
    • Avalanches/ Landslides.
    • Building collapse: Often results in casualties.
    • Tsunamis: Triggered by undersea quakes.
    • Subsidence: Ground sinking due to seismic activities.

Understanding Earthquake Risks

  • Factors Influencing Hazard Analysis:
    • Geological processes and locations.
    • Severity and recurrence intervals of earthquakes.
    • Ability to make forecasts and who is at risk.

Man-made Earthquakes

  • Loading Earth's crust with structures like dams can induce earthquakes.
  • Injection of liquid waste into the ground can create pressure on existing faults.

Emergency Preparedness

  • Personal Planning:
    • Home inspections to ensure structural integrity.
    • Emergency kits: Include essentials like food, water, first aid, flashlight, radio, and hygiene supplies.

Conclusion

  • Awareness, preparedness, and understanding of seismology play crucial roles in mitigating earthquake risks and impacts.