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We investigate the preparatory phase of the 2009, Mw 6.1 L'Aquila earthquake in central Italy by analyzing the temporal evolution and spatial distribution of the seismic moment, M0, to radiated energy, ES. Our approach focuses on monitoring the deviations of the scaling between M0 and ES with respect to a model calibrated for the background seismicity. The temporal evolution of these deviations, defined as Energy Index (EI), identifies the onset of the activation phase 1 week before the mainshock. We show that foreshocks are characterized by a progressive increase in slip per unit stress, in agreement with the diffusion of highly pressurized fluids before the L'Aquila earthquake proposed by previous studies. Our results suggest that the largest events occur where energy index (EI) is highest, in agreement with the existing link between energy index (EI) and the mean loading stress. Plain Language Summary: Understanding how the machine generating large earthquakes works is one of the fundamental challenging scientific questions. Pioneering studies have shown that large magnitude earthquakes are sometimes anticipated by foreshocks and slip instabilities. Until now, retrospective analyses of foreshocks during the preparatory phase of large earthquakes have focused mainly on their distribution in space, time and magnitude. In this study, we show that also the dynamic properties of the rupture process associated to foreshocks evolve both in time and space. Our results indicate that the temporal evolution of radiated energy and size of small magnitude earthquakes provide useful information to identify the begin of the final activation phase of the 2009 Mw 6.1 L'Aquila, Italy, earthquake, in agreement with seismicity rate information. Our study suggests that, for the investigated case, foreshocks had dynamic characteristics distinct from those of normal rate (background) seismicity. Thus, it can contribute with new evidence to the open debate whether foreshocks are different phenomena from background seismicity. Key Points: We observe foreshocks dynamic characteristics before the 2009, Mw 6.1 L'Aquila earthquake in central ItalyDeviations of radiated energy over seismic moment from a reference model highlight the preparatory phase of the main eventForeshocks are characterized by a progressive increase in slip per unit stress, in agreement with diffusion of highly pressurized fluids [ABSTRACT FROM AUTHOR]

Three devastating earthquakes of MW ≥ 5.9 activated a complex system of high‐angle normal, antithetic, and sub‐horizontal detachment faults during the 2016–2017 central Italy seismic sequence. Waveform cross‐correlation based double‐difference location of nearly 400,000 aftershocks illuminate complex, fine‐scale structures of interacting fault zones. The Mt. Vettore–Mt. Bove (VB) normal fault exhibits wide and complex damage zones, including a system of bookshelf faults that intersects the detachment zone. In the Laga domain, a comparatively narrow, shallow dipping segment of the deep Mt. Gorzano fault progressively ruptures through the detachment zone in four subsequent MW ∼ 5.4 events. Reconstructed fault planes show that the detachment zone is fragmented in four sub‐horizontal, partly overlaying shear planes that correlated with the extent of the mainshock ruptures. We find a new, deep reaching seismic barrier that coincides with a bend in the VB fault and may play a role in controlling rupture evolution. Plain Language Summary: In 2016–2017, a sequence of three devastating earthquakes with magnitudes ∼6 near the towns of Amatrice, Visso, and Norcia in central Italy triggered hundreds of thousands of aftershocks. We compute high‐precision locations for these aftershocks that have the power to illuminate the fine‐scale structure of the complex system of intersecting and interacting faults that were activate during the sequence. The normal faults that ruptured during the three mainshocks are capped at ∼9 km depth by a sub‐horizontal detachment zone. The normal faults intersect the detachment at an acute angle, causing complex fault zone structures and fragmentation of the detachment where they intersect. We observe a deep reaching seismic barrier that we conclude may play a role in controlling rupture extent and evolution of large earthquakes along this section of the Apennines. In general, fault complexity here is higher than in similar sequences in 2009 near L'Aquila to the south and in 1997 near Colfiorito to the north. Key Points: Precise locations of 390,334 aftershocks of the 2016–2017 Central Italy sequence illuminate the complex normal fault systemA system of high‐angle bookshelf faults accommodates slip at the intersection between normal and detachment faultsA deep‐reaching seismic barrier is identified north of the Sibillini Thrust that may control the ruptures of large earthquakes [ABSTRACT FROM AUTHOR]

Terra Nova, 24, 52-61, 2012 Abstract We have analysed the history of seismic activity in the region of L'Aquila to compare the 2009 sequence with previous ones. Historical catalogues are exhaustive for large shocks, but not for small earthquakes and swarms. Our original compilation highlights repeated seismic sequences from 1315 ad to present. In the 20th century, at least 23 sequences affected the Abruzzi region, 8 of which were very close to L'Aquila. In previous centuries, we found evidence of at least 13 sequences around L'Aquila, with maximum magnitude ∼4 to ∼5. Only three sequences were followed by stronger shocks (1461, 1703 and 2009). However, many strong events of the region (1349, 1762, 1915, 1950) were not preceded by foreshocks. We describe here the last of these sequences (1985) showing its strong similarity with the 2009 one, except its final evolution (no large event in 1985). Our analysis suggests that seismic sequences alone cannot be considered straight forerunners of incoming strong events. [ABSTRACT FROM AUTHOR]

Terra Nova, 00, 1–7, 2009 Using the non-extensive statistics, the analysis of the magnitude distribution of the 2005–2009 seismicity of L'Aquila area (Central Italy), struck by a strong earthquake ( ML = 5.8) on 6 April 2009 (1:32 UTC), was performed. This was the strongest event of the sequence. The analysis of the frequency magnitude distribution of three time intervals – (1) from 16 April 2005 to 30 March 2009, (2) from 30 March 2009 to 6 April 2009, and (3) from 6 April 2009 to 1 July 2009 – reveals that the non-extensivity parameter q increases in the seismic interval (2), before the occurrence of the strongest L'Aquila event, indicating an increase in the degree of out-of-equilibrium state before the occurrence of the strongest event. [ABSTRACT FROM AUTHOR]