ALBERT

Beschreibung: 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 Mw 〉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. 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 Mw 6.3 earthquake was followed, the day after, by an Mw 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 Mw 5.8 and 5.7 that occurred within a few hours causing severe damage and destroying a school populated by children (Vallèe and Di Luccio, 2005). The 1997–1998 Umbria–Marche seismic sequence was characterized by two mainshocks breaking adjacent parts of two faults and occurring a few hours from each other (Pino and Mazza, 2000). Overall, this sequence numbered six shocks of moderate magnitude (5:2 ≤ Mw ≤ 6:0), occurring along a 40 km line. The 1980Irpinia earthquake, with surface-wave magnitude Ms 6.9, was indeed composed by the sequence of three distinct subevents, nucleating on different faults at intervals of about 20 s, resulting in a total seismic moment M0 2:6 × 1019 N·m (Pingue et al., 1993; Troise et al., 1998). This event caused about 3000 deaths and huge damage. In all the above cited sequences, the total length of the fractured fault zone was approximately the same, that is, about 50 km. In this article, we simulate a consecutive seismic sequence using the seismograms recorded during the Emilia sequence. Our hypothesis is that the design spectrum may be exceeded when the seven major (Mw 〉5) earthquakes were to occur one immediately after the other. As our results show, structures can be stressed by consecutive wavetrains, possibly characterized by an increase of acceleration and displacement amplitude due to resonance. The obtained results suggest that at least for specific design applications, such as for strategic structures (i.e., power plants, nuclear waste disposals, bridges, hospitals, etc.) seismic-hazard analyses and design spectra should take into account the possibility that several mainshocks can be triggered consecutively, resulting in a ground shaking highly increased in amplitude and duration.

Beschreibung: Published

Beschreibung: 970-976

Beschreibung: 6T. Studi di pericolosità sismica e da maremoto

Beschreibung: JCR Journal

Beschreibung: This article presents findings from two episodes of seismicity and gas emission that occurred on 7 October 2015 and 6 December 2019 in Campi Flegrei caldera. This caldera has been affected by long-term unrest since 2004. The 6 December 2019 episode, consisting of a swarm of 38 earthquakes (maximum duration magnitude 3.1, the largest between 1984 and March 2020), occurred at the end of a one month period characterized by an increase in the ground uplift rate from 0:19 0:01 to 0:72 0:05 mm= day. A sudden increase in the fumarolic tremor amplitude, which is a proxy of gas emissionrelated parameters recorded at Solfatara–Pisciarelli hydrothermal area (e.g., CO2 air concentration), was observed during the seismicity episode. The uplift rate decreased immediately after the swarm (0:10 0:01 mm= day), whereas the fumarolic tremor amplitude remained higher than that observed prior to the swarm. Through analyzing the time series of uplift recorded in Pozzuoli (central area of the caldera) from differential measurements on tide gauges, we were able to identify the 2015 episode. This episode was characterized by increasing uplift rates that culminated in a seismic swarm of 33 earthquakes on 7 October, which was followed by decreasing uplift rates. We computed double-difference locations of earthquakes from the two swarms and found that they located along a conduit-like path, coinciding with a high-resistivity contrast zone, previously identified by audiomagnetotelluric measurements. The focal mechanisms of the major earthquakes of both swarms indicate fault planes radial with respect to the maximum uplift area. These phenomena can be interpreted as episodes of the volcanic and (or) hydrothermal system pressurization that culminate in an injection of fluids along the conduit-like path, which behaves as a valve that allows fluid discharge and the temporary depressurization of the source region.

Beschreibung: Published

Beschreibung: 965–975

Beschreibung: 4V. Processi pre-eruttivi

Beschreibung: JCR Journal