Magnitude: Changing an Earthquake's Magnitude (downgrade/upgrade)

Why do seismologists change the magnitude of an earthquake?

There are often misunderstandings about why  seismologists change the magnitude of an earthquake. The magnitude isn't a simple assessment of a squiggle on a seismogram.

Obtaining an accurate preliminary magnitude can be difficult due not only to the complex processes that occur deep within the Earth, but because there are over a dozen techniques of for calculating the magnitude of an earthquake. In this animation we look at two magnitude scales, and use two examples of magnitude changing.

CLOSED CAPTIONING: .srt file is included with the downloiad. Use appropriate media player to utilize captioning.


Keypoints:

Factors in calculating the magnitude of an earthquake:

  • Amplitude of seismogram
  • Frequency of seismic wave
  • Time between P, S, and surface wave arrivals
  • Equation used to determine the magnitude
  • Orientation of the fault and how it moved
  • Distance the fault moved
  • Area of the moving fault
  • Rigidity of rock on both sides of the fault
  • Duration of the earthquake rupture
  • Kind of bedrock/soil on which the seimograph is built
  • How the waves traveled through the Earth
  • Characteristics & calibration of the seismograph instrument
  • Types of waves recorded
  • Size of the earthquake

Total Time: 6min 50s
Level: Novice

42MB

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