The seismotectonic characteristics of Slovenia

Slovenia with its neighbouring areas lies at the junction of the Alps, the Dinarides and the Pannonian basin. These belong to the three plates: Europe, Adria and Tisza. On the Slovenian territory itself converge the External Dinarides NW-SE oriented right lateral strike-slip faults, the Transdanubian Range NE-SW oriented left lateral strike-slip faults, and the Southern Alps E-W oriented thrusts. The direction of the principal stress a, (azimuth = 6 degrees, dip = 8 degrees) is determined under the assumption of uniform stress throughout the region. Dip of the least principal stress sigma(3) of 5 degrees is consistent with the regional strike-slip regime. Listed structures form a pure shear structural mechanism on a regional scale. In spite of geologic evidence of tectonic displacements along mentioned structures in the past, there is no surface expression of their recent activity. The lithospheric units of the investigated area were amalgamated together during Tertiary. The seismicity is not concentrated along the primary plate boundaries but is rather spread in a broad zone along their deformed rims. The seismicity is moderate with the average depth of earthquakes in Slovenia of 6.5 km, and 9 to 20 km for stronger earthquakes (M(LH) > 4.2). No surface rupture related to an earthquake has been detected to date in Slovenia. The territory of Slovenia and its neighbouring regions has been delineated into five seismogenic areas, i.e., the areas with similar and among themselves differentiable tectonic and seismological characteristics. They are the Eastern Alps, the Southern Alps, with the Friuli region as a separate unit, the External Dinarides, and the Transdanubian Range.