Multi-segment rupture of the 2016 Amatrice-Visso-Norcia seismic sequence (central Italy) constrained by the first high-quality catalog of Early Aftershocks

Abstract

We present the first high-quality catalog of early aftershocks of the three mainshocks of the 2016 central Italy Amatrice-Visso-Norcia normal faulting sequence. We located 10,574 manually picked aftershocks with a robust probabilistic, non-linear method achieving a significant improvement in the solution accuracy and magnitude completeness with respect to previous studies. Aftershock distribution and relocated mainshocks give insight into the complex architecture of major causative and subsidiary faults, thus providing crucial constraints on multi-segment rupture models. We document reactivation and kinematic inversion of a WNW-dipping listric structure, referable to the inherited Mts Sibillini Thrust (MST) that controlled segmentation of the causative normal faults. Spatial partitioning of aftershocks evidences that the MST lateral ramp had a dual control on rupture propagation, behaving as a barrier for the Amatrice and Visso mainshocks, and later as an asperity for the Norcia mainshock. We hypothesize that the Visso mainshock re-activated also the deep part of an optimally oriented preexisting thrust. Aftershock patterns reveal that the Amatrice Mw5.4 aftershock and the Norcia mainshock ruptured two distinct antithetic faults 3–4 km apart. Therefore, our results suggest to consider both the MST cross structure and the subsidiary antithetic fault in the finite-fault source modelling of the Norcia earthquake.

Heterogeneous Behavior of the Campotosto Normal Fault (Central Italy) Imaged by InSAR GPS and Strong-Motion Data: Insights from the 18 January 2017 Events

“…This swarm of moderate-size events is part of the 2016-2017 central Italy seismic sequence that affected the central Apennines starting on 24 August 2016 with a M W 6.0 event in the Amatrice area ( Figure 1), and then culminated with the 30 October 2016 M W 6.5 largest event [11]. The geodetic, seismological, and geological studies published so far (e.g., [11][12][13][14][15][16][17][18][19][20]) agree in attributing the bulk of the 2016-2017 central Italy seismic sequence to the progressive rupture of different segments of two main NW-SE striking extensional structures of the central Apennines, the Laga Mts., and Mt. Vettore-Mt.…”

Three dimensional Gravity Local Inversion Across the Area Struck by the 2016–2017 Seismic Events in Central Italy

“…A view of the meshes used for the inversions is provided as supporting information ( Figure S1), while parameters used in the GRAV3D algorithm are provided in Table 1. To improve discussion and contribute in validation of the resulting volumes after the inversions, we compare these volumes with catalogs of seismic events from Chiaraluce, Di Stefano, et al (2017) and from Improta et al (2019). In the local volume, the first catalog counts over 18,700 events with M ≥ 0.1 registered between 24 August 2016 and 29 November 2016 and located between depths of 21 and − 1.9 km.…”

“…It is interesting to compare the geometries and densities obtained after the inversion, with the spatial distribution of seismic events within the local volume (Figures 4(b), 4(c), and 5). In particular, we use events with seismic magnitude M ≥ 3 from the catalog of Chiaraluce, Di Stefano, et al (2017) and the relocated aftershocks catalog of Improta et al (2019). We note that the large majority of data from both catalogs locates in the intermediate volume (i.e., carbonates and evaporites) with deeper events located in the upper basement.…”

“…The 2016-2017 seismic sequence that occurred in the area counted several tens of thousands of events with M ≤ 6.5 between depths of 0 and 15 km (Chiaraluce, Di Stefano, et al, 2017;Improta et al, 2019) and two relevant mainshocks on 24 August 2016 with M w 6.0 and on 30 October 2016 with M w 6.5 (Figure 1(a)). Similar to northern areas along the active extension in the Apenninic belt (Barchi, 2002;Latorre et al, 2016;Mirabella et al, 2008), the majority of the events in the 2016-2017 sequence was located within the sedimentary units, above the basement sensu lato (e.g., Mancinelli et al, 2019;Porreca et al, 2018) strengthening the hypothesis that the basement, or the lithological change at the base of the sedimentary units, could exert a significant role in controlling the depth distribution of seismicity (Barchi, 2002;Mirabella et al, 2008).…”

Recognizing the waveform of a foreshock

“…confirms the sawtooth profile as a distinctive feature of foreshock activity. 1 Visso foreshock belong to this situation 31,34 . In this case a fraction of the stress is redistributed within the "no-aftershock" red zone but the remaining stress is concentrated within the green zone, leading to normal aftershock activity.…”