A minor earthquake with a magnitude of 1.9 occurred in Ruiselede (Wingene – West Flanders) at around 10 pm last night.
The minor earthquake has been the subject of lively discussion on social media in recent hours. Many residents not only felt it but also heard it.
The tremor was centred on Ruiselede, but residents of nearby Meulebeke, Izegem and Ardooie – and even as far afield as East Flanders – have reported hearing something.
Already more than 200 reports
Details of the earthquake can be found on the website of the Royal Observatory of Belgium. There, you can also report that you felt the earthquake. So far, more than 200 people have done so.
Most of them report having felt an intensity of 3. At this level, the tremors can be felt indoors. People at rest feel a slight sway or tremor. Suspended objects swing slightly from side to side, but the tremor causes no damage.
From pressure wave to acoustic wave
“Many people don’t make the connection with an earthquake when they hear the sound that could be a loud lorry passing by,” says weather presenter Geert Naessens. So how exactly is that sound produced? “In the case of a shallow earthquake like this, a pressure wave that travels towards the Earth’s surface is generated.”
“You can imagine a pressure wave like that as a pulling and shoving of matter. As soon as that pressure wave reaches the Earth’s surface, it transforms into an acoustic wave – in other words, a sound wave. That is why you hear a sound but do not feel any vibration.”
Anyone who was close to the earthquake probably experienced the sound as a dull thud. Those further away were more likely to have heard a rumbling. “Just like a lorry, in other words.”
Unusual?
Just how unusual is this, actually? “A minor earthquake like this occurs about 10 to 20 times a year,” says seismologist Koen Van Noten. “But usually, nobody feels a thing. The fact that people have actually felt it this time is quite unusual.”
‘It doesn’t happen very often, particularly not in West Flanders,’ explains Van Noten. ‘The rock there lies in a much deeper layer of the earth. It is precisely in that rock that earthquakes occur. The fact that so many reports about the earthquake are now coming in is certainly due to the fact that people in West Flanders are absolutely not used to it.’
The previous earthquake in West Flanders took place on 2 August 2011 in Veldegem (Zedelgem). “Back then, we also received 500 reports,” adds Van Noten.