The earthquake in Slovakia 260 years ago killed. Seismologist: It can happen again

In recent weeks, after the huge earthquake in Turkey and Syria, the media reported on several tremors in different parts of the world. At the end of February, weaker tremors were also recorded near the Ukrainian village of Veľká Dobroň, approximately 15 kilometers from the border with Slovakia. In our territory, the last time the earth shook more strongly was in 2020 near Michalovce. After this event, there was damage to some buildings, for example the Sztáray mansion, the headquarters of the Zemplín Museum, or the control tower in the Biela hora garrison training ground.

Seismologists ANDREJ CIPCIAR (AC) and RÓBERT KYSEL (RK) from the Institute of Earth Sciences of the Slovak Academy of Sciences say that Zemplín is one of the seismically active areas in our territory. In the same way, the whole of Slovakia is relatively tectonically active from a geological point of view.

Most of the recent earthquakes in our country were considered weak on a global scale. However, in the past, our ancestors also faced earthquakes that toppled buildings and took human lives. Seismologists reassure us that we do not have to fear an earthquake similar to the one in Turkey, but such tremors as occurred near Komárno 260 years ago can be repeated here.

Since the earthquake in Turkey and Syria, reports of similar, albeit milder, events have begun to appear somewhat more frequently around the world. The media reported on the earthquake in Croatia, Romania, New Zealand and Wales. Are they somehow related, or are they separate phenomena that just happened at a time close to the devastating event in Turkey?

– AC: All mentioned are areas where the occurrence of earthquakes is not unusual and I assume that they are not related. The area of ​​New Zealand is part of the so-called Pacific Ring of Fire, which surrounds the base of the Pacific Ocean. About 90 percent of all earthquakes occur on it. Its total length is more than 40,000 kilometers.

In Europe, the wider area of ​​the Mediterranean Sea is the most seismically active. The aforementioned areas of Croatia and Romania belong to this zone, which continues through Turkey and then roughly southeast to Iraq, Iran, and the northern edge of India to the Himalayas.

Great Britain is not so seismically active, but it is still more active than the territory of Slovakia. About 300 to 400 earthquakes occur annually on its territory, while the most active part is North-West and South Wales.

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Earthquakes most often occur at the edges of large tectonic plates, as was the case in Turkey. At the same time, the largest magnitudes were also measured in these places. However, the Earth also shakes inside the plates. What is the cause?

– AC: The vast majority of earthquakes are of tectonic origin. This means that they occur at tectonic interfaces, that is, at faults due to the mutual movement of tectonic plates. People usually think of tectonic plates, if at all, of the 12 main ones that are in constant mutual movement. When comparing the location of the epicenters of earthquakes with the locations of tectonic interfaces, we see a significant agreement.

However, these main tectonic plates are further internally broken into smaller plates up to microplates. There are quite a lot of them, their mutual movement is often much more complicated than with the main plates, but earthquakes also occur at their interfaces. These are usually the ones “inside the plates”, but they happen on smaller local faults, which tend to be much more difficult to identify.

Seismologist and your colleague Kristián Csicsay said loudly in the morning podcast that earthquakes can be expected where they have already happened before. But does it also happen that the epicenter appears in a place where it has never been before?

– AC: We have to realize that compared to geological time, we only have a relatively short window of time for earthquake data. Instrumental seismology has been working for about a hundred years, we have historical data on earthquakes for about 1,000 to 1,500 years. If the tectonic movements are large, such as in the subduction zones of the Pacific Ring of Fire at about two to ten centimeters per year, the stress between the tectonic plates needed to cause an earthquake builds up quickly and earthquakes occur more frequently.

It is precisely during those “intra-plate” earthquakes, however, that it often happens that the tectonic movements are very small, and it can take hundreds to thousands of years before sufficient tension accumulates in the location of the wedge to cause an earthquake. Then, when an earthquake occurs, it may seem that there has never been one in that place before. But it could have been there a long time ago, we just don’t have information about it so long ago. In that case, it is possible that the tectonic fault operates in such a slow mode and further earthquakes will occur with a similarly long periodicity.

The second possibility is that as a result of the complicated mutual movement of tectonic plates, a new active fault has really been created. In that case, it is possible that we will start to observe earthquakes more often in the given area.

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Let’s go back to Croatia. The recent earthquake on the island of Krk had a magnitude of 4.8. Even in previous years, tremors were recorded in the country, they even damaged buildings, and in 2020 victims were also reported. From this point of view, is Croatia considered a dangerous country?

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