Intensities and magnitudes in natural science

[DaveC426913]

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?

 

[Andy Resnick]

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.