News agencies report a megaquake at Lake Baikal on June 8th, earthquake surveys don't. Censorship? Propaganda? Warfare? An explanation:
Magnitude 8.4 at Lake Baikal. Magnitude 8.4 in the densely populated heart of Siberia. Magnitude 8.4 near the major city of Irkutsk. With such headlines, Russian and international media have caused great confusion over the past two days. Not because they were describing the aftermath of a major disaster, but because such an earthquake of catastrophic proportions was not reported. At least not reported by western seismic services. Some users see censorship or propaganda, others an act of war by the USA (Haarp-conspiracy). But as usual, the explanation is simple.
On June 8th at 12:24 UTC the questionable earthquake happened. In the southern part of Lake Baikal, one of the region's many active faults has moved by a few centimetres, sending seismic waves around the globe. It wasn't a strong wave. Strong enough to shake high-rise buildings in the nearby city of Irkutsk, strong enough to frighten people on the nearest shores of Lake Baikal, but too weak to cause significant damage.
The global seismological network of the United States Geological Survey (USGS) determined a magnitude of 5.2 from the earthquake waves. The German Geoforschungszentrum (GFZ) ends up with Magnitude 5.0. Both calculated the Moment Magnitude, i.e. the value of the earthquake strength, which depends on the released energy. An increase of 1 magnitude means that 31x more energy was released. Deviations of 0.2, converted into energy, are very large uncertainties, not surprising because of the very isolated location (both networks have hardly any stations in Siberia and Central Asia). Earthquake determination is like darts. Everyone wants a 180, but sometimes a darts goes into a single 20.
Or even further away, if one compares the magnitudes of the western seismic services with the data communicated by the Russian authorities. "Magnitude" 8.3 or "Magnitude" 8.4. That would be a 100,000-fold energy release compared to the value of the GFZ. Or to stick with the darts metaphor: Instead of a 180 a hit in the beer glass of the man with the Aston Villa jersey on the back left of the Ally Pally. A rather embarrassing throw for a World Cup participant or a globally leading earthquake service.
But if you read carefully, and this is precisely what is crucial when asking the question, you will see that “magnitude” does not appear at all in the crucial text passages. Let's look at the exact wording of the Ria Nowosti news agency. If you don't speak Russian, Google translator can help:
An earthquake with an intensity of 8.3 points occurred on Lake Baikal, said the head of the Ministry of Emergency Situations in the Irkutsk region.
"’The epicenter was located 17 kilometers from the village of Bolshoe Goloustnoye in the waters of Lake Baikal. The intensity at the epicentre was 8.3 points. Up to five points were felt in the cities of the region’, the report says."
The crucial word here is “Intensity”. Intensity and magnitude are different ways to measure the size of an earthquake. While magnitude, as moment magnitude, usually refers to the energy release or the strength of the earthquake (in sense of geophysical process), intensity describes the actual effect of this earthquake. Or in other words: How strong is the shaking that I feel? How severe are its effects and the caused damages?
Let’s have a look at a western news agency, in this example Anadolu:
“Magnitude 8.4 earthquake recorded in Russia“
This report falsely uses the word “Magnitude” instead of intensity.
And similar in this Spanish “Marca”-report.
Here the word “Grados” is used which usually refers to a classic magnitude scale as well but wasn’t specified in this case. However, the missing piece of information will surely not have clarified any question.
International media (and even more bloggers, YouTubers and Putinfluencers) have adopted the intensity data measured by the Russian authorities as a supposed magnitude data. Intensity given instead of magnitude is standard in Russia, as well as in Japan and in Taiwan. Only a few Russian media (e.g. Lenta) have pointed this out directly in their reporting.
Magnitude 8.3 (or 8.4) would be a fatal disaster and the most powerful earthquake ever recorded in the region. Lots of fatalities and damage that actually didn't happen.
However, the confusion between Magnitude and Intensity was not the only reason for this mess. If you are familiar with earthquakes and intensities, you might have noticed that Intensity 8 (or 8.4) given for a Magnitude 5 (or 5.2) earthquake is quite a lot. Only a few cases over the past years are known where a quake of this size created such an intensity. But also, this can be explained easily.
Russian authorities have used an automatic magnitude determination to calculate this assumed (not measured!) intensity. Therefore, an initial value of Magnitude 6.4 was given, later corrected to Magnitude 5.2 though. Additionally, the maximum intensity calculation was given for the epicentre itself, which was located beneath the Lake Baikal and not very close to a settlement.
Earthquake calculations should be as accurate as possible. It is not just a random number, but ultimately decisive to be able to quickly assess possible damage and thus organize rescue measures. Instead of a rough magnitude, which is often meaningless regarding the possible effects, many countries such as Japan, Taiwan or Russia use precise intensity data also in public communication. 180, without Single-20. Unlike in Japan and Taiwan, however, the intensity is not measured but calculated in Russia. This opens the door to such misstatements based on incorrect magnitudes.
Several factors that further contributed to an extreme case of false earthquake reporting. However, wrong initial magnitudes are not unusual, not even at USGS, GFZ or other agencies, and strongly depending on the density of seismic network and external influences. No matter how you’re your Darts is, you will earlier or later hit a 1. Therefore, one should always wait for manual revision by a seismologist and communicate all uncertainties and differences precisely.