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Fractures, karstic cavities, and calcite precipitates are analysed on Mesozoic, carbonate strata from the Cornicolani Mountains, central Italy, to quantify the relationships between fractures and related karstic cavities and to infer the fracture-controlled fluid pathways. The study area is characterized by active sinkholes and other karstic caves, which are among the deepest ones in the world. Results show a clear control of fractures on the process of dissolutional weathering and, therefore, on the fluid circulation. A model is proposed, in which two different modes of dissolutional weathering coexist: (i) a mode of diffuse weathering consisting in the dissolutional enlargement of closely spaced joints and bedding surfaces. This process affects the strata situated at depths of up to 5 m; (ii) a mode of more concentrated weathering active along highly permeable fault damage zones at depths of at least 70 m. These processes are mostly connected with the shallow circulation of calcite-dissolving meteoric waters, and are controlled by the disparity of permeability between the fault damage zones and the surrounding jointed strata. Some calcite precipitates along the studied fault damage zones may be connected with a dissolutional process operated by waters that interacted with the adjacent quiescent volcanic district. Such calcite-dissolving waters and the presence of high-permeable fault damage zones, along which the waters may ascent, are probably the cause for the development of some of the deep sinkholes along faults in the study area.

This study identifies units characterized by specific geomechanical behaviours within some Holocene alluvial deposits in the City of Rome. In particular, the highly compressible units, which may be responsible for subsidence and settlement phenomena below urban structures, have been identified. Investigations carried out during this study have interpreted nearly 800 stratigraphic sections and physical–mechanical features of the alluvial deposits of the Tiber and those of its right- and left-bank tributaries. The analysis allowed to define, for each investigated deposit, a representative series subdivided into lithotechnical units. When comparing the stratigraphic and geologic features among the series, a remarkable difference in geomechanical behaviour in the deposits from the Tiber's left- and right-bank tributaries and within the river's deposits themselves could be recognized. A yield hazard zoning for urban structures related to recent alluvial deposits has also been defined.

An integrated structural, anisotropy of magnetic susceptibility (AMS) and paleomagnetic study was carried out on Plio-Pleistocene sedimentary basins in eastern Sicily. These basins belong to three main tectonic domains: the Tyrrhenian hinterland domain, the Catania foredeep domain, and the Hyblean foreland domain. We sampled 329 oriented samples from 25 sites in selected areas from the different tectonic domains. The AMS is typical for weakly deformed sediments, with a magnetic foliation sub-parallel to the bedding plane, and a well-defined magnetic lineation. The orientation of the magnetic lineation is strongly controlled by the main tectonic deformation recorded in the basins. Structural and AMS data define a transition from NW–SE extension in the Tyrrhenian hinterland domain, to E–W compression in the Catania foredeep domain, to E–W extension in the Hyblean foreland domain, respectively. Reliable paleomagnetic results have been obtained in 12 out of 25 sampled sites. Data show that no significant rotations occurred in any of the studied basins at least since the middle Pleistocene. These results allow us to define an upper limit to the large rotations about vertical axes that have been previously found in the Calabria and Sicily regions.

Resurgent blocks are uplifted parts of volcanoes where most of the deformation (uplift) is accommodated along peripheral faults. The island of Ischia (Italy) has an active resurgent block uplifted ~1000 m in the last ~30 ka and thus permits to investigate the deformation associated with a strong uplift in volcanic areas. Remote sensing interpretation was matched with field work (1:5000 scale mapping and structural analysis) throughout the resurgent block. These results have been matched with a review of the seismic and hydrothermal activity at Ischia. The results show that the block has a polygonal shape in map view and is characterized by a trapdoor uplift, which results in a ~15° tilt towards SE. The northern, most uplifted part, is bordered by E-W and NE-SW trending faults, arranged in parallel segments over an area ~1.5 km wide. I0 ≥ 5 MCS degree shallow (1-2 km depth) earthquakes focused in correspondence with the outermost set of faults on the northernmost part of the block. Here systematic variations in the hydrothermal activity have been observed during seismic events. Previously performed analogue models show that resurgent blocks are bordered by inward dipping high angle reverse faults (outermost fault system) and outward dipping normal faults (innermost fault system). We propose a model of trapdoor uplift of a block which induces reverse faulting, responsible for seismicity and hydrothermal variations along the most uplifted part. Outward dipping normal faults, in the innermost part, form due to the gravitational sliding of the volumes bordered by the reverse faults. The further reactivation of the outermost reverse faults triggers a new cycle new cycle of intermittent trapdoor uplift of the block.

Field and photogeological studies were made of 90 zones of interacting fracture segments along the rift zone of Iceland. Each zone consists of a pair of extension fractures or a pair of normal faults, with lengths from metres to kilometres. These zones evolve from an underlapping stage, through an overlapping stage (the most common configuration) and, finally, to a linkage stage. Of all the zones, only 7% are underlapping, whereas 93% are overlapping, with hook-shaped fracture pairs. The length/width ratios of the overlapping zones have a mean value of 3.5. The preferred geometry of the overlapping zones depends upon the initial configuration of the interacting fractures (length, overstep) and the development of the interaction. In the overlapping zones, most fracture pairs show moderate shear (strike-slip) components, related to local variations in the extension (opening) directions. Vertical displacements on normal faults decrease as the overstep and length of overlapping zones increase; both, in turn, are proportional to the total lengths of the faults forming the pair. The geometrical and kinematic features of overlapping spreading centres at mid-ocean ridges show close similarities to those reported here. These similarities indicate that the architecture and evolution of overlapping zones are scale independent.

The volcanic island of Ischia is located on the Tyrrhenian margin of Central Italy, characterized by Plio-Quaternary NW–SE- and NE–SW-trending extensional fractures. Ischia displays a resurgent dome uplifted by at least 800 m in the last 33 ka. Remote sensing and field data have been collected to study the structural setting of the island, the deformation pattern associated with resurgence and the superimposition of the regional and the resurgence-induced stress fields. NW–SE and NE–SW extensional fracture systems predominate throughout the island and around the resurgent block, suggesting a relationship with the regional extensional structures. These systems were formed before resurgence and were partly reactivated during resurgence. The reactivation of pre-existing regional systems during resurgence confined the extent of the uplifted area. N–S- and E–W-trending systems have been found exclusively at the borders of the dome and are interpreted as being induced by resurgence. The topmost resurgent block shows an octagonal shape in map view and is tilted at an angle of 15° around a NE–SW-trending horizontal axis; the block is partly bordered by high-angle, inward-dipping regional faults. More than 90% in volume of the volcanic products coeval with resurgence on Ischia have been erupted outside the resurgent block area, suggesting that the resurgence process locally replaced volcanic activity in the last 33 ka.

Results are presented of structural analysis and anisotropy of magnetic susceptibility (AMS) analysis of Plio-Pleistocene clayey units from the extensional Tyrrhenian margin of central Italy. Data have been collected in different tectonic settings, mainly strike-slip and transverse extensional structures. At the sites with major evidence of Plio-Pleistocene tectonics, there appears a close relationship between magnetic lineations and stretching directions. Stretching processes that were able to modify the original magnetic fabric pre-dated significant normal-fault-related tilting, and therefore were active at the very first stage of extensional deformation. The relationships between AMS and structural trends in an extensional regime seem distinctively different from those reported in compressional regimes. This kind of analysis may be useful in the geodynamic interpretation of ambiguous structures.