The mechanism of earthquake occurrence in the Pannonian Basin is not clear in most cases (in other words, it is often not possible to find a relationship between the location of epicenters and the elements of the maps of recent tectonic movements), hence a GIS has been created in order to clarify the origin of these events. The special seismological GIS includes all relevant information (maps and joint database) concerned with earthquakes covering the whole territory of Hungary. GIS contains the following maps: special macro- and microseismic epicenters and their parameters; different active tectonic fault maps; digital terrain model of the recent relief; digital terrain models of different geological basements; appropriate geophysical anomaly maps; Quaternary sediment thickness; recent rivers, water streams and settlements. GIS enables us to carry out special operations between different layers by applying its tools in order to reveal the recent tectonic movements and to throw light upon the generation of possible earthquake occurrences. Results of the present investigation in GIS revealed that significant relation exists between the earthquake foci and recent tectonic lines. Some foci, however, can not be related to fracture lines. One part of earthquakes showed agreement with Pre-Tertiary basement areas of considerable slope, with the recent tectonic elements of Geomorphological maps and with the piedmonts of the North Hungarian Range. Some traces of recent movements have been found with the help of the multiplication map of Quaternary sediment thickness map and Recent relief (Digital Elevation Model).
In this paper, a theory describing the possible origin of shallow depth earthquakes occurring within the sedimentary depressions of the Pannonian Basin is presented. In addition, the seismicity of Budapest is re-evaluated by synthetic seismogram based deterministic seismic hazard estimation.
Analysing the areal distribution of earthquakes produced in the Carpathian Basin the conclusion can be drawn that only certain parts can be considered active along fracture lines, namely those parts which separate individually moving blocks. Generally accepted working theory states that if one fracture line ever generated an M-magnitude earthquake then at any point of the same line a similar or larger tremor may happen again. However, this principle is not supported by domestic experiences. In accordance with focal depths analysis we are going to verify that earthquakes were produced within more or less consolidated layers inside subsiding basins. Our analysis is aimed to explain the possible origin of earthquakes within small depth range and to point out the practical benefit of these investigations. We present also an analysis on the possible origin of „basin tremors” not taken so far into consideration and we offer a plausible explanation. Uncertainties of focal depth (hypocenter) determinations will also be given and we define relations between the focal depth (h), the magnitude (M), and the epicentral intensity (Io). The result will be presented in tables and comparison will be given between the focal depth data determined by us and by others. Finally viewpoints will be presented to help the recognition of earthquake foci and to set earthquake hazard determination on a real basis.
Authors:Gy. Szeidovitz, R. Gutdeutsch, and Péter Varga
The seismicity of the Pannonian Basin is not yet understood. To improve our knowledge in this field the geological position as well as the damages caused by the biggest known earthquake of the inner part of the Pannonian Basin, i.e. the Komárom earthquake of 1763 was investigated. It is shown that this earthquake had probably an epicentral intensity of 9.5 MSK, and its origin was in connection with the Rába-Hurbanovo tectonic line.
Authors:Gy Szeidovitz, I. Paskaleva, K. Gribovszki, K. Kostov, G. Surány, P. Varga, and G. Nikolov
Karst regions are very vulnerable with respect to natural and human-activity related hazards. Some of them with beautiful caves were proposed to be of national value. The examination of broken and slim intact speleothems in Bulgarian caves (Varteshkata and Elata caves, western part of Balkan Mountain Range, North-West Bulgaria) allows estimating an upper limit for horizontal peak ground acceleration (PGA) generated by paleo-earthquakes.The density, the Young’s modulus and the tensile failure stress of the samples originating from broken speleothems have been measured in a laboratory.The fundamental frequency and damping of speleothems have been measured in cavity by in situ observations.The value of the upper limit horizontal ground acceleration resulting in failure and the natural frequency of speleothems were assessed by theoretical calculations using mechanical parameters — the density, the Young’s modulus and the tensile failure stress — of the samples originating from a broken speleothem from Elata cave.The ages of the samples taken from the investigated stalagmites have been determined by alpha spectrometry.The pure elastic behaviour in analytical modeling and calculations have been used.According to our modeling results the investigated speleothem has not been excited by a horizontal acceleration higher than 0.144 g in case of Varteshkata cave, and 0.326 g in case of Elata cave during the last few thousand years. These results can serve to improve the present seismic risk policy for karst regions, too.
Authors:Z. Wéber, Z. Bus, K. Gribovszki, B. Süle, Gy Szeidovitz, and P. Varga
In this paper, research activities at the Theoretical Division of the Seismology Department of GGRI (in short: Seismological Observatory) are summarized. The reported investigations have been carried out since 1999, when the division was founded with three members. Detailed discussions of the presented results can be found in various national and international scientific journals.