Macroseismic investigations of the geological site effects on intensities of selected earthquakes in greater Ljubljana area

Abstract

Ljubljana is one of three regions with the highest seismic hazard in Slovenia. In addition soft sediments in the Ljubljana basin have a strong influence on seismic ground motion. We used macroseismic data to investigate the influence of local geological structure on earthquake intensities in greater Ljubljana area. We determined intensities for eleven earthquakes according to ground classification based on Eurocode 8 standard (EC8). The results showed a systematic increase in observed seismic intensities, determined according to European Macroseismic Scale (EMS-98), as the seismogeological characteristics of the ground deteriorated. Only one ground type (D) showed slightly lower intensities than expected. This may be due to some unrevealed geological and other factors, or because of very limited macroseismic data available for this particular ground type.