## Thursday, March 11, 2010

### The Richter Scale – Not Testable

This is not testable. But someone asked for this (Kyle, I think), and here it is.

There are two ways to think about the strength of an earthquake as measured by the Richter scale.

One is the amount of back and forth shaking – what you see in movies when the needle goes back and forth.

The other one is the amount of energy released by the quake.

The former is better correlated with damage, but the latter allows reporters to draw pointless analogies — like how many Hiroshima-sized bombs this quake was equivalent to.

For both measures, the Richter scale is a base 10 log, so you have to reverse that to back out the actual value. On a calculator that usually means keying in something like “2nd function”, and then “log”. In Excel, you can do this by raising 10 to the power of the Richter scale reading.

So shaking in Chile was 63-times worse than in Haiti (10^8.8 divided by 10^7.0).

Energy released is measured by taking that ratio and raising it to the 1.5 power, making the Chilean quake 501 times as strong.

This is why the number I used in class to quantify the two quakes was different from what you may have heard in the media.