Earth and Space Science / Unit 4: Earthquakes and Volcanoes
4.5 Earthquake Magnitude and Intensity
Notes
- Magnitude measures the energy released at the source. The moment magnitude scale is used today (Richter was the older scale).
- Each whole number increase is about 32 times more energy and 10 times larger wave amplitude.
- Intensity measures shaking and damage at a place, using the Modified Mercalli scale (I to XII). It varies with distance and ground type.
- Example: a magnitude 7 releases about $32 \times 32 \approx 1000$ times more energy than a magnitude 5.
Practice
A magnitude 6 earthquake compared with a magnitude 5 releases about:
Each step is about 32 times more energy.
The Modified Mercalli scale measures:
It is an intensity scale.
Compared with a magnitude 4 earthquake, a magnitude 6 has seismic wave amplitudes that are:
Each whole number is 10 times larger; two steps give $10^2 = 100$.
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