Have you heard that a recent earthquake registered, say, seven “on the Richter scale”?
Well, it probably hasn’t, and the source that brought you the disturbing news may not be very knowledgable in modern seismology.
The fact is, professionals have abandoned the use of the Richter scale decades ago, having replaced it with a better designed system to evaluate earthquakes.
So nowadays any reference to Richter is most probably due to the old media cliché living its own scientifically inaccurate life.
What’s wrong with the Richter scale?
The Richter magnitude scale was proposed in the 1930s by a team of Californian seismologists led by Charles Francis Richter, and was largely based on the sensitivity of one particular type of contemporary seismographers. Nowadays we have much better instruments which allow to detect micro-earthquakes of such a small amplitude that it would make less than zero on the Richter scale.
On the other hand, some of the earthquakes occurring in particularly turbulent underground areas of the planet can be so strong that they surpass Richter scale’s upper limit. That’s due to the fact that the old scale was best suited to quantify medium-sized quakes typical for California, where Richter and his colleagues worked.
As the result, all the most powerful seismic events would tend to be falling into the same Richter’s category 7, regardless of their exact scale.
So, what instead?
In late 1970s, seismologists have came up with the current standard known as the moment magnitude scale. While its values are similar to the old system as long as we’re dealing with medium-sized earthquakes, it works much better when measuring horribly devastating seismic shocks that Richter didn’t address well in his formula.
The moment magnitude scale has no upper limit, so in theory it can address seismic waves of any power. It’s also much more accurate when dealing with relatively weak shocks detected with modern seismographic infrastructure.
So the correct way to reference the scale of modern earthquakes would simply be “magnitude five” or “magnitude seven”. No need to reference Richter anymore.