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.
Highlights
In recent years, three earthquakes of magnitude between 6.1 and 6.3 struck northern and central Italy, causing more than 600 victims and heavy socio-economic consequences in the epicentral areas: the 2009 L’Aquila earthquake; the 2012 Emilia earthquake (Mw 6.1, 26 deaths) and the 2016 Central Italy earthquake (Mw 6.2, 299 deaths)
Having identified a geographical divide in earthquake mortality, we explored its possible dependence on the systematic differences of the physical properties of the earthquakes occurring in northern and southern Italy
During the last century we have observed a progressive reduction of the number of victims caused by earthquakes in Italy: from tens of thousands at the beginning of the 20th century (1908, Calabria-Messina; 1915, Marsica), to thousands in the seismic cycle of around 1970 (1968, Belice; 1976, Friuli; 1980, Irpinia), to hundreds in the last seismic cycle of the last decade (2009, L’Aquila,; 2012, Emilia; 2016, Central Italy)
Summary
Three earthquakes of magnitude between 6.1 and 6.3 struck northern and central Italy, causing more than 600 victims and heavy socio-economic consequences in the epicentral areas: the 2009 L’Aquila earthquake (moment magnitude Mw 6.3, 309 deaths); the 2012 Emilia earthquake (Mw 6.1, 26 deaths) and the 2016 Central Italy earthquake (Mw 6.2, 299 deaths). 3274 the entire national territory was reclassified into four areas of decreasing danger, enumerated from 1 to 4 In this case, the introduction of a new seismic building code was accelerated by the occurrence of an earthquake (2002, Molise earthquake, magnitude Mw 5.7) and its tragic impacts (the collapse of a school killing 26 schoolchildren and one teacher). They lead to a discussion on the quality of buildings in Italy and its evolution over time. For the events from 1800 to 1997 we used the catalog CFTIMed5 [Guidoboni et al, 2018, 2019] that collects, for each earthquake, both the seismological parameters (time of the earthquake, epicentral coordinates and moment magnitude Mw) and the number of casualties. It has a time correspondence with the volcanic activity in Italy, especially in the area of Naples [Bragato, 2015, 2018], and has been interpreted as the expression of large-scale triggering processes, possibly related to the increased atmospheric precipitation during the Little Ice Age [Bragato and Holzhauser, 2019]
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