History of Hungarian earthquake's observation
In Hungary, the first seismometers were bought in 1891: The 10 seismoscopes were made by Lepsius, notes about their placement do not remain. The progressive instrumental registration started at 1 May 1902 in Budapest with a mounted seismograph made by Omori-Gablovitz in the basement of the Institute of Geology promoted and organized by The Seismic Committee.
Later the Central Observatory was placed in the basement of the National Museum, where one of the most modern seismographs (made by Wiechert) was set going in 1906 and worked without any mistakes through 60 years. The Hungarian network had 5 stations at this time (Budapest, Fiume, Ógyalla, Temesvár and Zagreb), and expanded with 5 more stations (Kalocsa, Kecskemét, Cluj (Kolozsvár), Szeged and Ungvár).
World War I broke this rapid development; our technical backwardness grew year by year in the situation formed after the World War II. This situation got to the point that in the 1990s we came to hear of an earthquake arisen in Hungary when people felt this. In 1995, we managed to set up a modern observation network with 10 stations, mainly for seismological monitoring of the settlement of the nuclear power-station in Paks. In 1999, this network expanded with three more measuring stations, to observe the projected place of the radioactive junkyard at Üveghuta. The secondary product of this project with industrial purposes recently we have a kind of measuring network, which makes the recording of less than perceptible quakes determination of their hypocentre in the expressive part of Hungary. Mutual exchanging data with seismological stations of neighbouring countries greatly helps this work.
At the end of 1990, 17 seismograph stations work in Hungary. With the help of this sensitive seismograph-network we measure an average 50-100 smaller (M<2) earthquakes, which knowledge helps a lot to recognize the source-regions of potential larger earthquakes.
The seismicity of Hungary
Until now, in Hungary earthquakes greater than M=6 Richter-magnitude, or 9o Mercalli intensity have not been noted, for this reason according to the definition we reckon Hungary's territory as aseismic area. At the same time in Hungary, there have been about 10 such earthquakes in this century, which have the intensity of 7o < I0 < 9o on Mercalli's scale. Although these not too many quakes, but if we have a look at the scale, which indicates the damage's level, then it will excel, that such strong quakes have serious destroying effect. In Hungary, the number and the strength of quakes are smaller, than to the South from Hungary, on the Balkan Peninsula, but larger than the areas, which are lying to the North from the Carpathian-basin. If we analyse the frequency of the earthquakes, we can find out, that on Hungary's territory there are quakes occurring with the intensity of 6o in average 4-5 yearly, with the intensity of 7o in average 11 yearly and quakes with the intensity of 8o in average 30 yearly.
The Alp-Himalayan active zone is lying nearest to Hungary. One part of the quakes, which have occurred in the Carpathian-basin, is probably connected to the pushing of the African plate towards Europe, but there are also other reasons for Hungarian earthquakes.
Focal-mechanisms of the Hungarian earthquakes
In Hungary big quakes occur rarely. The decisive majority of its quakes can only be registered by nearby stations (Hungarian and the neighbouring countries' stations). The condition of the focal-mechanisms' definition is, that as much as possible stations record quake. In this manner, we aren't able to determinate the focal-mechanism of most Hungarian quake with the above method, or the authenticity of the result is questionable.
However, in this way it was possible to successfully calculate the focal-mechanism solution of not a few quakes. The result is visible on the lower illustration. There are the lower hemispheres of the focal spheres in stereographic projection. The compressional space quarters (the direction of the maximal tension) are white, the dilatationals are dark. On the basis of the picture that is unambiguous, there is no indicatable characteristic tension direction to the whole Pannon-basin.
Mouse by its side: Characteristic compression space quarters of quakes.
From the focal-mechanism solutions an other physical amount is also deducable: the largest horizontal direction of tension (SHmax). You can see the SHmax directions if you take the mouse over the image. On the illustration, we can notice more regularity than the previous. The SHmax's ruling direction has turned from the experienced north-to-south on the west side of the country to the direction of northeast-to-southwest on the east side of the country, but there are many places, which don't follow this trend.
Based on the quakes' frequency in the time range from the middle of XIX. century till nowadays, practically there are four-five quakes, yearly, in the country with 2.5-3.0 magnitude, which are well perceptible in the surroundings of the epicentre, but they don't cause damage. Quakes, which cause significant damages occur every 15-20 years, while strong quakes, which cause very great damage occur every 40-50 years, they have the magnitude of 5.5-6.0.
Hungarian earthquake predicting
Earthquake can occur anywhere and at any time, but the inhabitants of the following settlements and those environs would sense them most frequently: Berhida, Dunaharaszti, Eger, Kecskemét, Komárom, Várpalota.
Hungary is not the part of the far and away earthquake-dangerous areas, but despite strong quakes can occur occasionally. In the course of these, the life of those who stay in non-convenient planned buildings could be endangered. However, the probability of occurring casualties as a result of an earthquake is negligible considering to the danger-sources of the everyday life.
A long time ago...
For examining the cause of the earthquake in 1810 at Mór's surrounding - which claimed human life and heavy building damages -, the Royal council of governor-general sent Kitaibel, Tomtsányi and Fabrici university teachers from Budapest. They expounded two ideas, according to the one the subsurface coals fire and vapour formed in the holes, which pressure suddenly pushed out the layers above it. According to the other idea, the subsurface electronic discharges called the quakes into being.
There weren't instrumental watchings, they didn't know, that the quakes could occur in 10-20 kilometres and below depth. They didn't find enough proof beside of either theory. Therefore, it's not surprising, that for their study's motto, they chose a quotation from Seneca: "Maybe our scions will be amazed, that we don't know such simple things." Since then almost two hundred years passed by. However, the earthquake science grew many, but we feel the truth of this quotation even now.
Hungarian earthquake history
The earthquakes' focal depth could expand from some kilometre to 600-700 kilometres, but the decisive majority of the quakes occur in 30 kilometres depth at most. Luckily the quakes are rare in Hungary, and the strength of them - according to experiences until now - does not exceed the IX. degree on the intensity scale. The first earthquake occurred in 456 in the environment of Savaria (Szombathely). According to the chronicles, the quake devastated the city. Unfortunately, we know little about the next, more than 1000 years' earthquake history. The earthquake of Komárom in 1763 considerably promoted Hungarian earthquake research. In the quake, 63 people died, 102 people were wounded and 7 churches, 279 dwelling fully and 353 partially collapsed. The hypocentre of Komárom is preserved its greater activity, and until 1857 on the average of each 20 years it generates quakes, which cause larger building damage. Grosszinger, a Jesuit priest probably wrote the first Hungarian earthquake-catalogue because the effect of this earthquake-series. Fortunately, the source calmed down, and only smaller quakes sign the activity of subsurface powers. In the course of the quake of Mór in 1810, heavy building damages were originated firstly in Mór and in Isztimér, here the intensity of the quake reached the VIII. degree. Two very strong quakes occurred in 1829 and in 1834 at Érmellék (Romania). The quake in 1834 also caused building damages in Kassa, Eger and Békéscsaba. The Hungarian studies show, that usually after the main quake, there are only smaller aftershocks, but exactly these two quake in Érmellék with almost same strength shows, that we can't give satisfying answer to the question, in spite of the fact, that we would like to satisfy the people. In the XX. century, firstly the sources of Kecskemét, Eger, Dunaharaszti and Berhida are activated. Although fortunately these quakes are caused heavy building damages, but they didn't claimed human life. The essence of present predicting methods is, that they follow closely the accompanying processes of tension's accumulation. It is possible to show the rearranging and moving of masses with geodetical and gravity measurements in one part of cases. The subsurface movements could open, close the aquifer layers in different depths, because of these the depth of ground water or the water output of wells could change. The unusual behaviour of animals also could warn to the approach of a huge earthquake.
The earthquake of Dunaharaszti in 1956
Similar, but lesser changes have been experienced in Hungary. In case of the earthquake of Dunaharaszti in 1956, in the 70-80 kilometres environment of the quake. Before the eruption of the quake, they just re-measured the upper-class levelling network and there were 4-5 cm closing mistakes in certain areas. In the beginning, they suspected errors of measurement, but the quake of Dunaharaszti in 1956 made the cause clear. Before the eruption of the earthquake, there were different transformations in the earth's crust, near the epicentre. Namely, this is why the assembled levelling polygons (made from the levelling lines, in the near surroundings of the epicentre of Dunaharaszti) are closed badly. In accordance with the elastic rebound's hypothesis, the experienced height-changes till then, suddenly have the opposite meaning after the earthquake and they changed back to the state before the deformation within a short time, moreover the level changes exceed the dimension of the deformations before the quake at some place near the epicentre.