Intensities and magnitudes in natural science

DaveC426913
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Main Question or Discussion Point

My friend edits grade school textbooks and often has science questions. While I pretty much know the answers, I like to get them verified from more reliable sources.

This is once such question asked:

earthquakes vs. hurricanes
Why do we measure the magnitude of earthquakes, but the intensity of hurricanes?

Just an interesting choice of words?
This was my response:
An "order of magnitude" is an increase by a common <b>factor</b>, usually ten.

10 is an order of magnitude larger than 1;
1000 is an order of magnitude larger than 100.

This is how Earthquakes are measured. Each increase of a number by one is an order of magnitude greater in energy release of the quake. i.e. a mag 7 earthquake is 10 times larger than a mag 6, which is 10x larger than a mag 5.

Hurricane measurement uses a more linear approach: Intensity is an increase by a common constant. The categories 1-5 are more or less the same size i.e. a Category 5 is about 35kmh greater than a Category 4, which is about 35kmh greater than a Category 3.


So, in a nutshell, intensity measures changes on a linear scale, whereas magnitude measures changes on a geometric scale.
True? I mean is this why Earthquakes are measured as magnitudes while hurricanes are measured as intensities?
 
Last edited:

Answers and Replies

Andy Resnick
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Interesting question- the Fujita scale of tornado *intensity* has rough agreement with your reasoning for hurricane intensity.... there is an earthquake intensity scale (Mercalli)...

Do you know anything about the development of these scales? That may give a clue.
 

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