The Ljubljana 1895 earthquake: source parametres from the inversion of macroseismic data

The 14 April 1895 earthquake (Mw 6.1, in the Ljubljana area, Slovenia) is still not fully explained. The aim of this paper is to derive information on its source from the inversion of an updated dataset of intensities (evaluated using EMS-98). This was done by the KF-NGA automatic non-linear geophysical inversion, with a Niching Genetic Algorithm technique, already presented in other articles. The distribution of damage caused by this earthquake is not homogeneous, often with significant differences of intensity between neighboring sites. The statistical analysis of intensities, epicentral distances and sites geology suggests some site effects. Despite this, the resulting solution is compatible with the regional seismotectonics, i.e. an almost pure dip-slip mechanism: strike angle 282°5°, dip 38°±7°, rake 86°±9° (±180° because of the intrinsic ambiguity of the KF-NGA inversion). Since the rake angle is close to 90°, there is an almost perfect ambiguity between the two planes of the focal mechanism. Thus, our solution has a Dinaric direction and could be associated with either a fault plane dipping NE or with one dipping SW.