- © 2014 by the Seismological Society of America
Online Material: Earthquake catalogs; Kolmogorov–Smirnov test results.
Northern Italy (considered as the territory located north of latitude 44° N for this paper; Fig. 1) is situated at the convergence of the northern sector of the Adriatic microplate with the Eurasian plate. It includes the deep (2–8.5 km) sedimentary basin of the Po Plain surrounded by the seismically active structures of the northern Apennines, southern Alps, and northern Dinarides. Present kinematics derived from Global Positioning System measurements (Cenni et al., 2012) indicates a movement of the central–eastern sector in the northeast direction toward the Eurasian plate at a rate of a few millimeters per year, which results in a mainly compressive tectonic style. The area is characterized by moderate–strong seismicity, with five Mw>6 earthquakes in the last century (Rovida et al., 2011). It contributes in a significant way to the overall seismic risk of the country because it is densely populated (231 inhabitants per km2, or about 28 million in total [ISTAT, 2012]) and has a large number of economically important activities.
According to the Italian Seismological Instrumental and Parametric DataBase (ISIDe; ISIDe Working Group, 2010), fifteen ML 4–5.4 mainshocks struck northern Italy between 2005 and 2010 (2.5 per year on average). After these years of scarce seismicity, between July 2011 and June 2012 the entire area was subjected to an almost simultaneous reactivation, with a series of 12 ML≥4 mainshocks (black diamonds in Figs. 2 and 3; the corresponding location parameters and magnitude are reported in Table S1, available in the electronic supplement to this paper). They originated in different, often well‐separated, …