PATTERNS OF EARTHQUAKE DAMAGE IN STON: A 146-YEAR COMPARISON

The medieval town of Ston in southern Dalmatia (Croatia) has experienced several significant earthquakes since the mid-19th century, notably the ones in 1850 and 1996. While the macroseismic parameters as well as classification of damage to buildings in Ston related to the 1996 event are available from previous studies, the 1850 earthquake has only recently undergone detailed macroseismic analysis. It revealed clear similarities between the two events, including their epicenters, focal depths, and epicentral intensities. To enable comparison of the spatial distribution of damage from these twin earthquakes, we combined historical damage reports from 1850 with cadastral records from 1837. This allowed us to geolocate most of the damaged buildings, despite challenges in identifying individual structures due to changes in ownership and building modifications over the intervening years. Our study indicates that both earthquakes caused the most significant damage in the plain area below Bartolomija Hill, characterized by a sedimentary cover 10–30 m thick, with expected ground motion amplification by factors between 3 and 5. In contrast, the hillsides of Bartolomija in the northern part of the city, with their shallow or outcropping bedrock, experienced minimal damage from both events. To our knowledge, this observation of the shaking effects for two strong similar earthquakes in a city that has changed little in the 146 years between them is unique in Croatia. It demonstrates consistency of spatial pattern of earthquake ground motion amplification for comparable input earthquake motion.