“Stronger tremors are heard rather than felt. The sound resembles the rumble of a passing truck. Sometimes the ground even shakes slightly. If you have glasses close to each other in the display case, they will clink,” Monika Filandrová, who lives in Luby near Cheb, a few kilometers from the epicenter of the earthquake, told Seznam Zprávám about the current shocks. “So far, the tremors were felt most strongly yesterday, today they seem weaker,” he adds.
Seismographs at the Institute of Geophysics of the Academy of Sciences say otherwise. Today at 12:58 p.m., the strongest earthquake of magnitude 3.3 was recorded at a depth of 9.3 kilometers, near the village of Černá between Luby u Cheb and Kraslice.
A series of weaker tremors (M<2.2) occurred in western Bohemia this afternoon, see the daily seismogram below. The epicenters of these phenomena lie approximately between Luby and Kraslice. It could be the start of a new seismic swarm - we are monitoring the activity. pic.twitter.com/bqMIcpbRLI
— GFÚ AVČR (@GFU_AVCR) November 1, 2023
“Since Wednesday afternoon, we have been in the so-called seismic swarm period, when we recorded over a thousand smaller tremors. Today’s was the strongest so far,” says seismologist Jakub Klicpera from the Institute of Geophysics of the Academy of Sciences of the Czech Republic in an interview for Nauzal.
How to perceive today’s (Saturday’s) shock in the context of the aforementioned seismic swarm?
This is the strongest shock so far, which people have certainly already felt on their own skin. The so-called seismic swarm has been going on since Wednesday and it is difficult to judge where it will develop. The activity may end on Monday, or it may last for months. We cannot estimate that.
The epicenter is located between the towns of Luby u Cheb and Kraslice, i.e. in the most seismically active area in the republic. For us scientists, the seismic swarm is of course very interesting, but it is definitely not pleasant for people. And the human point of view is of course the most important.
If you were to describe the power of today’s earthquake in reality, what did the people in Chebsk probably feel?
When the tremor exceeds three degrees, chandeliers swing and glasses clink. But they’re just moving, not falling off the shelves yet. It is interesting that earthquakes in western Bohemia are quite often accompanied by sound effects. People describe it as a rumble, a thunderstorm, a passing train, or something similar. The sound of an earthquake is caused by shaking the earth’s surface and the sound wave spreading through the landscape. Kind of like having a diaphragm on a speaker.
How often do these seismic swarms occur?
For a few years, we recorded isolated tremors, but there were no seismic swarms. I think the last stronger one was in 2018. So far, I would consider the current one more or less average, but everyone perceives it individually. Some local people see it as an attraction and just wave their hand, others are scared because it’s annoying, like the ceilings swaying.
What does this period mean for you seismologists?
When the seismic swarm ends, so let’s dive into more detailed processing and map out which fault surface what happened. We will find out if some other break has been activated, or if it is happening on an existing break.
When you have classic earthquakes like the last one in Morocco or Turkey, you get a big shock and then a series of small smaller aftershocks. Our situation is unique in that we do not have a big earthquake, but a so-called aftershock sequence, where energy is released slowly and gradually during many small earthquakes. People only notice a few more significant tremors, like today’s, but in reality there are over a thousand of them.