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.

 

[astrokreng]

Yes, that is correct. The reason for this difference is due to the nature of the phenomena being measured. Earthquakes release energy in a logarithmic manner, meaning that each increase in magnitude represents a significant increase in energy release. This is why it is more appropriate to use a scale that measures orders of magnitude.

On the other hand, hurricanes release energy in a more linear manner, meaning that each increase in intensity represents a relatively consistent increase in wind speed. Therefore, it is more appropriate to use a scale that measures changes in intensity on a linear scale.

Additionally, the measurement of hurricanes also takes into account other factors such as pressure and storm surge, which cannot be easily measured on a magnitude scale. Overall, the use of different scales for measuring earthquakes and hurricanes is based on the most effective and accurate way to measure and understand these natural phenomena.