A new earthquake scale is needed

Keith Hudson

Yesterday’s earthquake in Kent didn’t reach me here in recumbent Somerset but it has jolted me into writing about what is a very silly scale that’s used when comparing the power of earthquakes.  The Kent earthquake with a magnitude . . . of 4.2 on the Richter Scale was nowhere near more half the shaking power of the recent earthquakes in Nepal — 7.8 — or even the later aftershock of 7.3 (which actually was a great deal weaker, though it doesn’t seem like that on the scale — and nor was to the people, still in shock from the original one).

Seismologists have no problem with the Richter Scale because they are used to thinking in logarithmic terms.  They know, for example that an earthquake of 5.0 is actually 10 times more powerful than one rated 4.0 and this, in turn has ten times the power of a 3.0 earthquake.  But the general public who read and hear these figures in the media don’t treat them that way.  This means that the Kent earthquake — which was barely strong enough to knock a plastic garden chair  over — newspapers had a hard time finding anything to photograph! — seemed to be quite a strong one on the figure alone.

On the other hand, we, in the more pacific parts of the world, when we hear of a 6.0 or 7.0 or 8.0 earthquake occurring somewhere else in the world, can have absolutely no idea of just how powerful they are.  We demand photos, preferably of collapsed buildings or bridges or great rents running along highways before we can grasp its importance.  Then again, when we hear of a powerful 7.0 earthquake we have no idea just how deep it actually was.  If it’s very deep it has nowehere near the devastating power than a similarly rated one that occurs near the ground level.

In actuality, the Kent earthquake of 4.2 was only something between one thousandth and one ten thousandth the power of the 7.8 Nepalese earthquake.  Why doesn’t one of the world’s seismologists calibrate a new scale for the media ans we simpletons to understand  — from 1 to 100, say, or, better, from 1 to 1,000.  The last is a number that even the most innumerate person can grasp. The figure of 1 could be that of a slight rumble — as of a heavy lorry passing by, say —  and 1,000 could be that of a powerful earthquake that may only happen once in a thousand years.

Thus, on the proposed Hudson scale, if the Nepalese earthquake were to register, say, 800, the Kent earthquake would be 2 or 3 — no more.  That gives a sensible comparison in terms of devastation.  Incidentally, what is now so obvious when we see the damage of recent earthquakes in the media — say, that of Chistchurch in New Zealand (6.3) in 2011 and the recent Nepalese one — is how well modern buildings stand up to them.  Thus Japanese or Californian people who can expect very powerful earthquakes not all that infrequently are little worried by them (or they don’t seem to be!).  But what sort of earthquake could demolish even the best designed building?  My guess is that it would have to be 9.0 on the Richter scale or 950 on mine — but then the next one is probably a few hundred years away from now!

Of course, the horrifying thing about earthquakes is that, unfortunately, they’re so complex that seismologists are not a great deal nearer being able to forecast them.  Perhaps this will be rectified in due course but considering the depth of some earthquakes, and the jaggedness of the edges of the tectonic plates that cause them, it wouldn’t bet on it.

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