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The prompt identification of faults responsible for moderate‐to‐large earthquakes is fundamental for understanding the likelihood of further, potentially damaging events. This is increasingly challenging when the activated fault is an offshore buried thrust, where neither coseismic surface ruptures nor GPS/InSAR deformation data are available after an earthquake. We show that on 9 November 2022, an Mw 5.5 earthquake offshore Pesaro ruptured a portion of the buried Northern Apennines thrust front (the Cornelia thrust system [CTS]). By post‐processing and interpreting the seismic reflection profiles crossing this thrust system, we determined that the activated fault (CTS) is an arcuate 30‐km‐long, NW‐SE striking, SW dipping thrust and that older structures at its footwall possibly influenced its position and geometry. The activation of adjacent segments of the thrust system is a plausible scenario that deserves to be further investigated to understand the full earthquake potential of this offshore seismogenic source. Plain Language Summary: The Northern Apennines chain is characterized by thrust faults running from the Po Plain to the Adriatic Sea on the northeastern side of peninsular Italy. These thrusts are buried below ≈2,000 m cover of Plio‐Pleistocene deposits. Controversies arose about these thrust faults' activity and earthquake potential based on their hidden geological signature and the scanty seismicity that could be associated with them. The earthquake (magnitude 5.5) that occurred on 9 November 2022, offshore Pesaro revived this argument. In this work, we analyze the geological structure of the crustal volume affected by the seismic sequence, exploiting seismic reflection profiles and well‐log data to identify the earthquake causative fault. Our results demonstrate that the earthquake ruptured a well‐known fault of the Northern Apennines' buried thrust front, supporting that it is indeed active and seismogenic. The size and architecture of this thrust front suggest that it could generate even larger earthquakes (Mw > 6.5). This type of geological study is instrumental to understanding the geometry of earthquake faults, particularly in offshore areas, because they constitute reliable inputs for earthquake hazard models and, when done promptly after an earthquake, provide key elements for other studies on the seismic source and the unfolding of the ongoing seismic sequence. Key Points: 9 November 2022, earthquake consistent with activity of the Cornelia thrust, a fault system running off the central Adriatic coastThe seismic reflection profiles in the area allowed for delineating the thrust and its earthquake potential with a much finer resolutionThe properties of the causative fault suggest that the activation of adjacent segments is a plausible scenario that deserves consideration [ABSTRACT FROM AUTHOR]

Fluid overpressure is a primary mechanism behind fault interaction and earthquakes triggering. The Apennines section within the young Alpine mobile belt is a key locus to investigate the interplay between fluids and faults. Here, seismicity develops along the extending mountain belt and the key role of fluids has been invoked in past large earthquake sequences. In this study, we use seismological data to get improved images of the Apennines normal faulting system, trying to catch evidences for the involvement of fluids in the preparatory phase of large earthquakes. We observe that extension preferentially reutilizes inherited fragments of faults which were assembled during the Mio‐Pliocene contraction, with steep segments that floor on a regional‐scale gently east dipping plane. We find evidences for wide volumes of overpressured fluids at the base of the seismogenic layer, which are connected to the activation of the recent large earthquakes. The recognition of fluids compartments with overpressuring and diffusion molding seismicity is a key to understand faulting processes and possibly develop forecasts scenarios. [ABSTRACT FROM AUTHOR]

The potential role of subsequent tectonic phases in reworking inherited geological structures is a key issue to unravel the seismotectonics of an area. This has a direct connection with fault segmentation, earthquakes maximum magnitude, and strong implications for seismic hazard assessment. The central Apennines (Italy) represent an exemplary case, since it developed because of the overprint of different deformational phases, producing potential conditions for episodic tectonic inversions and a very complex structural architecture. In this paper, we show how inherited compressional structures, still dominating the Apennines belt architecture, interfere with the active extension, having a direct connection with active seismotectonics. We present seismicity and new velocity tomograms of an 80‐km‐long section of the normal fault system activated during the 2009 and 2016–2018 seismic sequences. The joint interpretation highlights how the extensional seismic sequences partially reactivated inherited compressive structures, which have not an undisputable relationship with the surficial geological setting. Complexity deriving from the irregular geometry of normal faults and inverted thrust ramps is responsible for the observed intense fragmentation of the extensional system. Fluid overpressure seems to be a viable mechanism behind the partial remobilization of unbroken segments of the fault system. Key Points: Tectonic inversions and fault segmentations represent the main process behind the current crustal arrangement of central ApenninesSurface versus deep expression of faults: subsequent deformational stages cause complex interaction between inherited extensional and compressional structuresFluid overpressure plays a role in the partial remobilization of unbroken fault segments [ABSTRACT FROM AUTHOR]

Wastewater injection into a high-rate well in the Val d'Agri oilfield, the largest in onshore Europe, has induced swarm microseismicity since the initiation of disposal in 2006. To investigate the reservoir structure and to track seismicity, we performed a high-spatial resolution local earthquake tomography using 1,281 natural and induced earthquakes recorded by local networks. The properties of the carbonate reservoir (rock fracturing, pore fluid pressure) and inherited faults control the occurrence and spatiotemporal distribution of seismicity. A low- Vp, high- Vp/ Vs region under the well represents a fluid saturated fault zone ruptured by induced seismicity. High- Vp, high- Vp/ Vs bumps match reservoir culminations indicating saturated liquid-bearing zones, whereas a very low Vp, low Vp/ Vs anomaly might represent a strongly fractured and depleted zone of the hydrocarbon reservoir characterized by significant fluid withdrawal. The comprehensive picture of the injection-linked seismicity obtained by integrating reservoir-scale tomography, high-precision earthquake locations, and geophysical and injection data suggests that the driving mechanism is the channeling of pore pressure perturbations through a high permeable fault damage zone within the reservoir. The damage zone surrounds a Pliocene reverse fault optimally oriented in the current extensional stress field. The ruptured damage zone measures 2 km along strike and 3 km along dip and is confined between low permeability ductile formations. Injection pressure is the primary parameter controlling seismicity rate. Our study underlines that local earthquake tomography also using wastewater-induced seismicity can give useful insights into the physical mechanism leading to these earthquakes. [ABSTRACT FROM AUTHOR]

The structural architecture of a portion of the eastern side of the Tyrrhenian Sea back-arc basin has been defined reinterpreting a public data set made up by seismic reflection profiles. A detailed reconstruction of the extensional front migration trough time across the area has been achieved. Migration has been defined by identifying the generation of unconformities in the graben-like basins developed in the area, as due to the activation and deactivation of normal faults. Such phenomena are part of a tectonic process that also involved blocks rotation, crustal thinning, and stretching. Syn-rift extension affected the area since the early to middle Miocene (our estimate), principally interesting the north-westernmost sectors. During late Miocene and throughout the Plio-Quaternary the extensional front moved stepwise toward the southeastern and eastern sectors. Widespread postrift conditions established over the whole area since the late Pliocene to early Pleistocene. Since the Quaternary, the locus of active extension further migrated toward the present onshore area, where a pronounced volcanic phase developed. In this evolutionary framework the rates of observed migration could be correlated with the acceleration of Calabrian slab rollback since Pliocene. Furthermore, direct evidences of magmatism were not recognized in the offshore. Although the observed crustal thinning, the absence of volcanic bodies in the study area could be related to normal faults which were unable to sufficiently extend the crust, in association with lower crust and mantle processes unable to produce melts. [ABSTRACT FROM AUTHOR]