Time-invariance and geographical divide of earthquake mortality in Italy since 1800

Abstract

We considered the mortality data of the earthquakes which occurred in Italy since 1800 and investigated their spatial-temporal characteristics. For this purpose, we developed a log-linear regression model relating the number of deaths to the magnitude of the earthquakes and analyzed the distribution of the residuals from the model. We found that, for fixed magnitude, the mortality of the earthquakes of the last decades is almost identical to that of the 19th century despite the fact that the population is decreasing in the small municipalities with high seismic hazard. There is also a geographical divide: for the same magnitude, an earthquake in southern Italy causes 2.9 times the number of victims than in northern Italy. The gap is partially justified by the higher population density in the seismic areas of southern Italy, while it does not seem to depend on seismological factors (seismic source, regional attenuation and site effects). The north/south divide increases to a factor of 8.3 for the earthquakes occurring between 00:00 and 05:00 a.m., when most people are sleeping and rely almost entirely on the strength of their houses for survival. We suggest that differences in the quality and maintenance level of the residential buildings are the primary factors determining this geographic divide, supported by data from a survey taken in 1934 and from the last general national census of 2011. Our results indicate that the situation of residential buildings in Italy requires a strict application of the seismic regulations as well as their extension to stimulate the correct maintenance and retrofitting of the existing buildings.