Author: M. Kiszely 1
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  • 1 Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences Meredek u. 18 H-1112 Budapest Hungary
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The Carpathian Basin is situated in the territory between the Mediterranean area, which is seismically one of the active regions and the Carpathian Mountains belt. The temporal variation of seismicity is investigated on the example of three seismo-tectonically different regions: the Carpathian Basin, the Vrancea region and the Dinarides. The seismicity is analyzed since 1900 in order to investigate the existence of diurnal periodicities using hodographs. There are two different diurnal distributions opposing each other: maximum early morning dominates until the year 1963, followed by a period of time when earthquakes seem to occur more often around 13h local time mainly concerning the weak M M < 3.2 events. The midday maximum in the number of minor events may be caused by the inclusion of quarry blasts, but the diurnal geomagnetic variations correlate well with diurnal changes in earthquake activity. Duma and Rhuzin (2003) suppose that the current vortices induced by Sq variations in the lithospheric layer, flowing across the horizontal component of the geomagnetic field generate a torque which can be added to the tectonic loading stress (which have a maximum about noon) and may help trigger instability in a fault approaching the failure threshold.The spatial and temporal fractal structures of earthquakes were analyzed using the box counting method. The regions were divided into different size r of a square box and were counted the minimum number N ( r ) of boxes necessary to cover all the data. The recurrence times of earthquakes are shown to be a clustering process and are much higher in the Carpathian Basin. The earthquakes in these regions have self-similar structures. The slope of log N -log r function for Carpathian Basin breaks at about 20 km, which divides the range into two bands. This breaking at about 20 km maybe connected to the intrinsic weakness of the Carpathian Basin lithosphere.