The 2012 Emilia, Italy, Quasi-Consecutive Triggered Mainshocks: Implications for Seismic Hazard

Abstract

The 2012 Emilia seismic sequence in central Italy represents an illustrative example of quasi‐consecutive triggering with several mainshocks occurring within a few hours or a few days. The sequence was characterized by seven earthquakes of moment magnitude M w>5, rupturing adjacent fault segments of the buried fold arc of the northern Apennines, for a total length of about 50 km (Scognamiglio et al. , 2012; Fig. 1). The occurrence of so many large earthquakes, in such a short time window, suggests a possible interpretation in terms of mutual, static (Ganas et al. , 2012), or dynamic (Convertito et al. , 2013) triggering. In this article, we discuss the consequences of a consecutive succession of earthquakes, that is, a succession of close earthquakes that occur almost simultaneously. Figure 1. Geographic representation of the area interested by the Emilia sequence. The figure shows the epicenters and magnitudes of the seven major events analyzed in this study (black stars). Gray stars represent the aftershocks of the whole sequence, whereas the black triangles identify the stations used to compute the response spectra. Multiple triggering—with variable time delays—has been observed in several damaging earthquake sequences of the Italian Apennine belt. In the central Apennines, the 2009 L’Aquila M w 6.3 earthquake was followed, the day after, by an M w 5.6 event occurred at the southeast edge of the main fault. This seismic sequence has been the deadliest one in Italy, with almost 300 victims, since 1980. The seismicity of the whole sequence spread over a 40 km long fault system (Chiarabba et al. , 2009). The 2002 Molise seismic sequence is remembered for two major shocks M w 5.8 and 5.7 that occurred within a few hours causing severe damage and destroying a school populated by children (Vallee and Di Luccio, 2005). The 1997–1998 Umbria–Marche seismic sequence was characterized by …