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