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Abstract: Presently thirteen seismological stations work in Hungary and hundreds of small earthquakes are detected yearly. The magnitude of 80% of the detected seismic events is ML≤2.0. If we compare this to the situation fifty years ago, when the catalogued events contained only the earthquakes that people felt, we understand that today in Hungary an important revolution is taking place in seismology. In this paper we investigate the statistical features of earthquakes and blasts in the Carpathian Basin and adjacent regions (16º-23ºE – 44.5º-49ºN). Three different methods were performed using data from the period 1995.01.01-2009-08.31 to investigate the existence of periodicities in the seismic events. A midday maxima is verified in the cases of earthquakes and blasts, and we found that there are fewer events on weekend and more during the summer. The increased number of earthquakes around 12 h (MET) might be attributed to the inclusion of quarry blasts among the earthquakes, however natural process might also contribute in triggering instability in a fault approaching the failure threshold around midday. Monthly variations in the distributions of seismic events might not be of physical origin, but connected to the changing sensitivity of the instruments during the seasons. The comparison of the diurnal distribution of earthquakes occurring on weekends and on weekdays indicates the contamination of the Hungarian Earthquake Bulletin with data from quarry blasts.

Keyword: earthquake, blast, seismicity, Carpathian Basin, diurnal, hodograph