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Records of the magnetometers responding to the effects of big earthquakes were noticed more than a hundred years ago. Even then began to dispute what caused these effects: mechanical vibrations of instruments or electric or magnetic oscillations generated by the earthquakes. In Panagjurishte (PAG) observatory we have great opportunity to shed light on this issue because we have four important instruments installed on the site - three different types of magnetometers and one seismometer. Three large earthquakes wit...

Global seismic risk and vulnerability to earthquakes are increasing steadily as urbanization and development occupy more areas that a prone to effects of strong earthquakes. The assessment of seismic hazard and generation of earthquake scenarios is the first link in the prevention chain and the first step in the evaluation of the seismic risk. The territory of Bulgaria represents a typical example of high seismic risk area in the eastern part of the Balkan Peninsula. Over the centuries, Bulgaria has experienced st...

Records of the magnetic variations are different at every observatory. They depend mainly on the latitude of the observatory and the local time. To give a quantitative measure of the amount of magnetic disturbance at any time, we need to rely on magnetic indices. Usually, local K-index is preferred as indicator of the geomagnetic activity in a specific area. Each observatory assigns a digit ranging from 0 to 9 to both H and D, for every three-hour interval starting at midnight, universal time (UT). Recently, in De...