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.

We present high‐resolution Vp and Vp/Vs models of the southern Apennines (Italy) computed using local earthquakes recorded from 2006 to 2011 with a graded inversion scheme that progressively resolves the crustal structure, from the large scale of the Apennines belt to the local scale of the normal fault system. High‐Vp bodies defined in the upper crust and midcrust under the external Apennines are interpreted as extensive mafic intrusions revealing anorogenic magmatism episodes that broadened on the Adriatic domain during Paleogene. Under the mountain belt, a low‐Vp region, annular to the Neapolitan volcanic district, indicates the existence of a thermal/fluid anomaly in the midcrust, coinciding with a shallow Moho and diffuse degassing of deeply derived CO₂. In the belt axial zone, low‐Vp/Vs gas‐pressurized rock volumes under the Apulian carbonates correlate to high heat flow, strong CO₂‐dominated gas emissions of mantle origin, and shallow carbonate reservoirs with pressurized CO₂ gas caps. We hypothesize that the pressurized fluid volumes located at the base of the active fault system influence the rupture process of large normal faulting earthquakes, like the 1980 Mw6.9 Irpinia event, and that major asperities are confined within the high‐Vp Apulian carbonates. This study confirms once more that preexisting structures of the Pliocene Apulian belt controlled the rupture propagation during the Irpinia earthquake. The main shock broke a ~30 km long, NE dipping seismogenic structure, whereas delayed ruptures (both the 20 s and the 40 s subevents) developed on antithetic faults, reactivating thrust faults located at the eastern edge of the Apulian belt.

The Campi Flegrei caldera is a large volcanic complex lying in the Campanian Plain, Southern Italy. During its history the caldera experienced episodes of bradyseism and intense swarm seismicity. The mechanism leading to unrest episodes is still debated, and great efforts are ongoing to improve the knowledge of this structure and its evolution due to the high volcanic risk in such a densely populated area. Here we present a resistivity model from a two‐dimensional inversion of audiomagnetotelluric data acquired along an approximately 5.6‐km long profile crosscutting the Solfatara‐Pisciarelli district and the Agnano plain. The resistivity model shows (1) very low resistivity values confined in the first 500 m of depth both in correspondence of the Solfatara‐Pisciarelli districts and the Agnano depression; (2) a resistive plume that extends underneath the Solfatara crater down to 2,000‐ to 3,000‐m depth, and (3) an adjoining relative conductive unit eastward. We discuss the resistivity structures in a multidisciplinary framework integrating inedited geochemical and seismological observations with existing surface geology and subsurface information. The Solfatara‐Pisciarelli district and the Agnano plain, both being expression of intense hydrothermal activity, show different characteristics. Below the Solfatara‐Pisciarelli area, the shallow conductive zone is interpreted as a faulted clay cap that overlies a highly active vapor‐dominated reservoir characterized by a convective mechanism. Conversely, below the Agnano plain, a liquid phase seems to prevail in the reservoir. The spatiotemporal variations of seismicity imply a combined action of preexisting tectonic lineaments and fluid interaction between the gas/steam reservoir and the outflow zone.

The Val d'Agri basin in the Apennines seismic belt hosts the largest oil field in onshore Europe. High‐quality recordings from a temporary dense network unravel a swarm of 111 small‐magnitude events (M_L ≤ 1.8) occurred in June 2006 during the first stage of wastewater injection into a high‐rate well. High‐precision relative locations define a preexisting blind fault located 1 km below the well inside fractured and saturated carbonates where wastewater is reinjected. Seismicity begins 3 h after the initiation of injection. The seismicity rate strictly correlates with injection curves and temporal variations of elastic and anisotropic parameters. Seismicity is induced by rapid communication of pore pressure perturbations along a high‐permeability fault zone favorably oriented with respect to the local extensional stress field. Our accurate 3‐D locations of 219 events (M_L ≤ 2.2) detected by the local operator network after June 2006 concentrate on the preexisting fault measuring 5 km along dip. Over the following 7.5 years, the seismicity rate correlates with short‐term increases in injection pressure.