22 December 2010

Did the earth move as much for you as for me?

Another example of things you thought you knew not always being true. According to the Guardian today a minor earthquake in Cumbria measured 3.5 on the Richter scale. Except it probably didn't.

The Telegraph got it right. In one of those annoying things scientists do, they've begun classifying earthquakes according to the Moment magnitude scale, which is better because it measures the actual movement of land (I think). Apparently this has been the preferred scale since the 80s.

The Daily Mail (no link - you know you want to thank me), the Sun (ditto), even the Independent also got it wrong.  How come I (and the Guardian and Independent) have never heard of it?

There are two big mistakes in the MMS. First, it was calibrated so that it pretty nearly matches the Richter scale. So the Cumbria quake probably would measure about 3.5 on the Richter scale, if anyone measured it that way. You can understand why they'd calibrate it that way, but it does allow for a certain confusion. Media can continue to refer to the Richter scale, without getting the figure seriously wrong. They get the official statement from Her Majesty's Earthquake Inspectorate (Offshake) read the figure of 3.5 and see something about magnitude, so assume it's the number of Richters.

The bigger mistake is that it hasn't got a memorable name. Even Sirlordsugar's hapless nitwits could come up with something better than "moment magnitude scale". It was devised by scientists called Hanks and Kanamori. Scientists estimate that up to 95% of all earthquakes happen in Japan, so why not just call it the Kanamori scale? Sorry, Prof Hanks, but we don't want confusion with light hollywood comedies to blur the picture.


Anonymous said...

Maybe the Graun got it right after all? According to the BGS:

"BGS detected an 3.5 ML earthquake at 22:59 UTC on 21 December located approximately 2 km north-north-west of Coniston, Cumbria. Many people throughout the Cumbria region felt the event."

Where the ML indicates 'Local Magnitude', aka the Richter scale. Apparently MMS or Mw is only reliable for larger earthquakes over magnitude 3.5...

I'll crawl back into the pedantic hole I came from now - thanks for piquing my interest enough to learn something new today!

Brian said...

Brilliant research, Alex, thanks. And what a bonus to find that the Telegraph got it wrong! This is sure to come up on QI sometime - what is the name of the scale used to measure the magnitude of earthquakes? Klaxon for Alan Davies.

Anonymous said...

Ah, but unfortunately the Telegraph is right too (or at least it is right now - they have been revising their version of events recently - "complete transcript" anyone?) when they say "... an earthquake of local magnitude 3.5, the term seismologists prefer to the Richter scale" (my italics).

The term "local magnitude" is preferred to Richter but it refers to the same thing.

I think your original point is valid though - I wonder how many people know that there are actually multiple scales for measuring the magnitude of earthquakes that give roughly the same number? I guess at least two more than there were yesterday...