Magnitude 7.8 or 7.4 on the Richter scale? The different measurements of the earthquake in Turkey

If you have followed the minute last minute about the earthquake that happened in Turkey, Syria and other neighboring countries, you will have seen a certain dance of figures on the magnitude of the tremor. 7.4 or 7.8, Richter scale or other measurements… What is the good? All the figures have their explanation, although not all of them are the most correct to use.

Some media, especially the Turkish ones, are using the magnitude of 7.4. When this figure is given, it is because the ML magnitude has been chosen, which is the equivalent to the measurement on the well-known Richter Scale.

The problem of this scale is that it “falls short” for large earthquakes like the one that took place in the early hours of this Monday and that is leaving some creepy images about the disaster caused. From 7 degrees of magnitude, the measurement of the Richter scale is not precise, according to Gerardo Alguacil, a researcher at the Andalusian Research Institute for Geophysics and Seismic Disaster Prevention and professor at the University of Granada.

Due to this limitation, for years the Richter scale is not used as an international standard, but the Mw, or “moment magnitude” is used.“, says the expert, has a range of validity that covers from small to large earthquakes.

The European and American seismic observatories have assessed the earthquake through this measurement, which is why in most of the European and international media the magnitude given is 7.8 -or 7.7, as also reported by the istanbul seismic observatory.

And in Spain, how do we measure it?

To further complicate the matter, it turns out that the National Geographic Institute (IGN), the body that measures earthquakes in Spain, uses another measurement system different from the ones mentioned above. Since 2002 -because the systems have changed over the years-, the IGN commonly uses the mbLg (L)“Magnitude from the amplitude of the Lg phase (López, 2008)”, as explained in his magnitude types guide.

Bailiff explains that this system is used because “it is easier and faster to calculate”, and it is valid for small earthquakes -normal in Spain-, while Mw requires more calculations.

Finally, the researcher points out, it is possible that we will still see a slight dance of figures regarding the magnitude of the earthquake in Turkey and Syria, because “many times these magnitudes are calculated automatically and then they are usually reviewed by an expert and you can refine” the data, although in this case you consider that you do not believe it will change and that in any case it would be a tenth at most. Tenth up or down, what will not change are the terrible consequences it is having both this earthquake and its replicas.