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We investigated the eastern corner of northeastern Italy, where a system of NW–SE-trending dextral strike-slip faults of western Slovenia intersects the south-verging fold and thrust belt of the eastern Southern Alps. The area suffered the largest earthquakes of the region, among which are the 1511 (Mw 6.3) event and the two major shocks of the 1976 seismic sequence, with Mw = 6.4 and 6.1. The Colle Villano thrust and the Borgo Faris–Cividale strike-slip fault have been here first analyzed by interpreting industrial seismic lines and then by performing morphotectonic and paleoseismological analyses. These different datasets indicate that the two structures define an active, coherent transpressive fault system that was activated twice in the past two millennia, with the last event occurring around the 15th–17th century. The chronological information and the location of the investigated fault system suggest its activation during the 1511 earthquake.

The general basin and range Apennine topographic characteristic is generally attributed to the presently active normal fault systems, whose long-term activity (throughout the Quaternary) is supposed to have been responsible for the creation of morphological/structural highs and lows. By coupling field geological survey and geophysical investigations, we reconstructed the 3-D geological model of an inner tectonic basin of the central Apennines, the Subequana Valley, bounded to the northeast by the southern segment of one of the major active and seismogenic normal faults of the Apennines, known as the Middle Aterno Valley–Subequana Valley fault system. Our analyses revealed that, since the late Pliocene, the basin evolved in a double half-graben configuration through a polyphase tectonic development. An early phase, Late Pliocene–Early Pleistocene in age, was controlled by the ENE–WSW-striking and SSE-dipping Avezzano–Bussi fault, that determined the formation of an early depocentre towards the N–NW. Subsequently, the main fault became the NW–SE-striking faults, which drove the formation during the Quaternary of a new fault-related depocentre towards the NE. By considering the available geological information, a similar structural evolution has likely involved three close tectonic basins aligned along the Avezzano–Bussi fault, namely the Fucino Basin, the Subequana Valley, and the Sulmona Basin, and it has been probably experienced by other tectonic basins of the chain. The present work therefore points out the role of pre-existing transverse tectonic structures, inherited by previous tectonic phases, in accommodating the ongoing tectonic deformation and, consequently, in influencing the structural characteristics of the major active normal faults. This has implications in terms of earthquake fault rupture propagation and segmentation. Lastly, the morpho-tectonic setting of the Apennine chain results from the superposition of deformation events whose geological legacy must be considered in a wider evolutionary perspective. Our results testify that a large-scale basin and range geomorphological feature – often adopted for morpho-tectonic and kinematic evaluations in active extensional contexts, as in the Apennines – just led by range-bounding active normal faults may be actually simplistic, as it could not be applied everywhere, owing to peculiar complexities of the local tectonic histories.

Since the beginning of the ongoing Amatrice seismic sequence on August 24, 2016, initiated by a Mw 6.0 normal faulting earthquake, the EMERGEO Working Group (an INGV team devoted to earthquake aftermath geological survey) set off to investigate any coseismic effects on the natural environment. Up to now, we surveyed about 750 km2 and collected more than 3200 geological observations as differently oriented tectonic fractures together with intermediate- to small- sized landslides, that were mapped in the whole area. The most impressive coseismic evidence was found along the known active Mt. Vettore fault system, where surface ruptures with clear vertical/horizontal offset were observed for more than 5 km, while unclear and discontinuous coseismic features were recorded along the Laga Mts. Fault systems.

Active faulting and deep-seated gravitational slope deformation (DGSD) are common geological hazards in mountain belts worldwide. In the Italian central Apennines, kilometer-thick carbonate sedimentary sequences are cut by major active normal faults that shape the landscape, generating intermontane basins. Geomorphological observations suggest that the DGSDs are commonly located in fault footwalls. We selected five mountain slopes affected by DGSD and exposing the footwall of active seismogenic normal faults exhumed from 2 to 0.5 km depth. Field structural analysis of the slopes shows that DGSDs exploit preexisting surfaces formed both at depth and near the ground surface by tectonic faulting and, locally, by gravitational collapse. Furthermore, the exposure of sharp scarps along mountain slopes in the central Apennines can be enhanced either by surface seismic rupturing or gravitational movements (e.g., DGSD) or by a combination of the two. At the microscale, DGSDs accommodate deformation mechanisms similar to those associated with tectonic faulting. The widespread compaction of micro-grains (e.g., clast indentation), observed in the matrix of both normal faults and DGSD slip zones, is consistent with clast fragmentation, fluid-infiltration, and congruent pressure-solution active at low ambient temperatures (<60°C) and lithostatic pressures (<80 MPa). Although clast comminution is more intense in the slip zones of normal faults because of the larger displacement accommodated, we are not able to find microstructural markers that allow us to uniquely distinguish faults from DGSDs., (© Wiley Periodicals LLC. The Authors.)

We measured ground displacements before and after the 2009 L'Aquila earthquake using multi-temporal InSAR techniques to identify seismic precursor signals. We estimated the ground deformation and its temporal evolution by exploiting a large dataset of SAR imagery that spans seventy-two months before and sixteen months after the mainshock. These satellite data show that up to 15 mm of subsidence occurred beginning three years before the mainshock. This deformation occurred within two Quaternary basins that are located close to the epicentral area and are filled with sediments hosting multi-layer aquifers. After the earthquake, the same basins experienced up to 12 mm of uplift over approximately nine months. Before the earthquake, the rocks at depth dilated, and fractures opened. Consequently, fluids migrated into the dilated volume, thereby lowering the groundwater table in the carbonate hydrostructures and in the hydrologically connected multi-layer aquifers within the basins. This process caused the elastic consolidation of the fine-grained sediments within the basins, resulting in the detected subsidence. After the earthquake, the fractures closed, and the deep fluids were squeezed out. The pre-seismic ground displacements were then recovered because the groundwater table rose and natural recharge of the shallow multi-layer aquifers occurred, which caused the observed uplift.