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Off the Scale!

Ted Nield bewails the popular persistence of “the Richter Scale”

Geoscientist 17.6 June 2007

One of the things that separates scientists from journalists is this. Scientists, like all academics, go through life learning more and more about less and less. We hacks on the other hand tend to learn more and more about more and more – and then to forget it all. Finding ourselves daily adrift in a sea of intellectual uncertainty, buffeted by a perfect storm of information from all points of the compass, we have a tendency to cling desperately to things that we think we know. One of those things is “the Richter Scale”.

Every journalist has written “An earthquake measuring 7.8 on the Richter Scale has struck the island of Sumatra….” at some stage in their career, and a week hardly passes when you cannot read it somewhere. But why?

Because first of all, it’s wrong. Seismologists no longer use the Richter Scale, defined in 1935 by the famous Californian nudist Charles F Richter (1900-1985) and Beno Gutenberg (1889-1960) of the California Institute of Technology (CIT). Although the idea of a logarithmic magnitude scale was first developed by Richter and Gutenberg, it was designed for measuring the size of earthquakes in southern California, and it used fairly high-frequency data from nearby seismographs. What eventually became known as the “Richter” magnitude was originally called “Local Magnitude” or ML. As more seismographs were set up around the world, it soon became apparent Richter’s method was strictly valid only within certain frequency and distance ranges. Like many things from California, it possessed certain magic characteristics.

New magnitude scales that extended Richter & Gutenberg’s original idea were developed as the number of recording stations worldwide increased. These include body-wave magnitude (Mb) and surface wave magnitude (Ms). Each is valid over a particular range of frequency and type of signal, and within its own parameters is equivalent to “Richter” magnitude. But because of the limitations of all three (especially the tendency to become saturated at high magnitudes, so that very large events cannot be easily distinguished) a more uniformly applicable magnitude scale, known as moment magnitude (Mw), was developed in 1979 by two other CIT scientists, Tom Hanks and Hiroo Kanamori. For very large earthquakes, Mw gives the most reliable estimate of earthquake size, and this is the measure that is always misreported as “the Richter Scale”.

OK – so much for the science bit. But ask yourself this - even if scientists did still use Richter, what real information would be conveyed by mentioning him? Forecasters may speak of Celsius and Fahrenheit, but only because there is a choice. Moreover, being correct and writing “An earthquake of Magnitude 7.8 has struck the island of Sumatra” is four words shorter. The chance to achieve correctness and concision at the same time ought to be welcomed by journalists everywhere – if only because the two coincide so rarely. Lastly, by not using the word “scale” we would avoid fostering the assumption, almost as mistaken as it is universal, that “the Richter Scale” has a top. (Or for that matter, a bottom. If this confuses you, just remember that the saying: “logarithmic plots are a device of the devil” is attributed to Richter.)

It is my theory that my fellow journalists cannot resist saying “on the Richter Scale” because like the epic poets, they rely heavily on repeated stock phrases – we call them clichés. Moreover, the public expects it. We are seeing a conspiracy - between journalists wishing to sound knowledgeable, and the public, which likes to flatter itself that it knows something, especially when it doesn’t.

Richter’s only remaining function, therefore, is to provide a beacon of false hope amid the choppy waters of ignorance in which we float. And for that reason, I fear that we shall go on clinging to him.