The Earthquake of 13 April 1850 near Ston, Croatia: Macroseismic Analyses

The earthquake that occurred near the city of Ston, Croatia, on 13 April 1850 is, together with the one from 1996, the strongest known event in the northwest part of the Dubrovnik epicentral area. This is the region with the highest seismic hazard in Croatia with a rich history of damaging earthquakes. Although listed in the relevant catalogs, this earthquake has never been addressed by a dedicated study. Herewith, we present analyses of a wealth of newly found material related to the damage and postearthquake actions of the authorities of the Province of Dalmatia, then a part of the Austrian Empire. We were able to estimate intensity at five localities, with a further six where the data were sufficient only to constrain the minimum intensity value. By far, most of the data refer to Ston and Dubrovnik. Intensity data points were inverted for the source parameters by two different methods, each of which yielded similar results. The focus is macroseismically located about 7 km east-southeast from Ston, at a depth of 9 km. Estimated epicentral intensity of 8.2 on the European macroseismic scale is equivalent to macroseismic local magnitude MmL=6.0 or the moment magnitude Mmw=5.9. The location of focus and the epicentral intensity are practically identical to those of the Ston–Slano earthquake of 1996. This is why we propose that these two earthquakes share the same composite seismogenic source consisting of a set of imbricated mostly reverse faults related to the basal thrust of the Dalmatian tectonic unit. The reliable location and quantification of the 1850 earthquake should contribute to a better understanding of the active dynamics of the set of large seismogenic faults in the Dubrovnik epicentral area.