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Earthquake Engineering

1.3 Earthquake measurement and scales

2 min readLast Updated on July 25, 2024

Earthquakes pack a powerful punch, and measuring their impact is crucial. From the Richter scale to the Modified Mercalli Intensity scale, scientists use various methods to quantify shaking and assess damage. These tools help us understand and prepare for seismic events.

But not all scales are created equal. The Richter scale, while groundbreaking, has limitations. Enter the moment magnitude scale, which provides a more accurate picture of earthquake energy across all types and depths. It's the gold standard for modern seismology.

Earthquake Measurement Fundamentals

Earthquake magnitude measurement

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Top images from around the web for Earthquake magnitude measurement
  • Earthquake magnitude quantifies energy released at source using logarithmic scale
  • Richter scale developed by Charles Richter in 1935 measures largest seismic wave amplitude
  • Calculated using formula M=logAlogA0M = \log A - \log A_0 (M: Magnitude, A: Maximum wave amplitude, A0A_0: Standard reference amplitude)
  • Seismographs record ground motion produce seismograms for analysis

Magnitude vs intensity

  • Magnitude objectively measures earthquake energy single value independent of location
  • Intensity subjectively assesses effects varies by location distance from epicenter local factors (geology, building quality, population density)
  • Higher magnitude generally correlates with higher intensity decreases with distance from epicenter

Advanced Measurement Scales

Modified Mercalli Intensity scale

  • 12-point scale (I to XII) developed by Giuseppe Mercalli modified by Wood and Neumann
  • Assesses observed effects on people structures environment
  • Key levels:
    1. I-III: Weak shaking barely noticeable
    2. IV-V: Light to moderate shaking felt by most
    3. VI-VII: Strong shaking minor to moderate damage
    4. VIII-IX: Severe shaking considerable damage
    5. X-XII: Extreme shaking widespread devastation
  • Used for rapid impact assessment historical analysis public communication

Limitations of Richter scale

  • Saturates at higher magnitudes (> 6.5-7.0)
  • Regional bias due to California-specific calibration
  • Inaccurate for deep earthquakes
  • Moment magnitude scale developed by Kanamori and Hanks in 1979 addresses limitations
  • Based on seismic moment M0=μADM_0 = \mu AD (μ\mu: Rock rigidity, A: Rupture area, D: Average displacement)
  • Moment magnitude formula Mw=23logM010.7M_w = \frac{2}{3}\log M_0 - 10.7
  • Advantages: no saturation applicable to all earthquake types depths directly related to fault properties
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© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.