The northern coast of Sicily and its offshore area represent a hinge zone between a sector of the Tyrrhenian Basin, characterized by the strongest crustal thinning, and the sector of the Sicilian belt which has emerged. This hinge zone is part of a wider W-E trending right-lateral shear zone, which has been affecting the Maghrebian Chain units since the Pliocene. Seismological and structural data have been used to evaluate the seismotectonic behavior of the area investigated here. Seismological analysis was performed on a data set of about 2100 seismic events which occurred between January 1988 and October 2002 in the Southern Tyrrhenian Sea. This paper focuses in particular on a set of data relating to the period from 6th September 2002, including both the main shock and about 540 aftershocks of the Palermo seismic sequence. The distribution of the hypocenters revealed the presence of two main seismogenic zones. The events of the easternmost zone may be related to the Ionian lithospheric slab diving beneath the Calabrian Arc. The seismicity associated with the westernmost zone is closely clustered around a sub-horizontal regression plane contained within the thinned Southern Tyrrhenian crust, hence suggesting that this seismogenic zone is strictly connected to the deformation field active within the hinge zone. On the basis of both structural and seismological data, the brittle deformation pattern is characterized by high-angle faults, mainly represented by transcurrent synthetic right-lateral and antithetic left-lateral systems, producing both restraining/uplifting and releasing/subsiding zones which accommodate strains developing in response to the current stress field (characterized by a maximum axis trending NW-SE) which has been active in the area since the Pliocene. The cluster of the seismic sequence which started with the 6th September 2002's main shock is located within the hinge zone. The distribution of the hypocenters relative to this sequence emphasizes the presence of a high-angle NE-SW-oriented deformation belt within which several shear surfaces are considered to be found sub-parallel to that established for the main shock. The kinematics of all these structures is consistent with a compressive right-lateral focal mechanism.

The main structural characteristics of the Caggiano and Polla faults, exposed in the epicentral area of the 1561 earthquake (Mw = 6.4), southern Italy, have been investigated in detail to assess their spatial and temporal properties, and to evaluate their seismogenic potential. These right stepping normal faults show an overlap of about 7 km and an across strike separation of about 4 km. The geometric relationships between the Caggiano and Polla faults, but also the displacement distribution along each fault, demonstrate that they have been strongly interacting throughout the Pleistocene. Nevertheless, geological evidence of Holocene tectonic activity was mainly recognized along the Caggiano Fault (faulted late glacial deposits) and in the southernmost part of the Polla Fault (faulted deposits of probably Late Pleistocene age). This suggests that the Caggiano Fault can be considered as the most tectonically active fault in the Vallo di Diano Fault System. By calculating Coulomb stress changes, we have constrained modes of mechanical interactions between the two faults in a scenario compatible with the 1561 earthquake. This approach allows us to argue that both the Caggiano and the Polla Faults are probably linked at depth, and part of the same seismogenic structure which may be potentially responsible for composite ruptures with magnitude >= 6.5. (C) 2008 Elsevier B.V. All rights reserved.

Detailed geological mapping and new stratigraphic and structural data collected in the Lucania area of the southern Apennines allowed us to assess the deformation history of 11 Monte-Corleto Perticara zone, in the High Agri Valley (Lucanian Apennines, southern Italy) where red and green shales (known as Argille Varicolori or Argille scagliose) crop out. Our observations suggest that: (1) 'chaotic' facies within the Argille Varicolori may be attributed to a broken formation generated by overthrusting of Apenninic Platform units onto already deformed Lagonegro basin strata; (2) gravity sliding phenomena at the thrust front enhanced the development of debris flow and the emplacement of olistostromes at distances of up to tens of kilometres from the leading edge of the Apenninic Platform thrust; (3) the above processes probably ended in mid-Miocene time, as suggested by observed structural and stratigraphic relationships among accreted terranes and synorogenic deposits. The evolutionary model envisaged here could also be relevant in other active convergent zones, where seismic and drilling data are sparse, and in subaerial fossil margins where broken formations occur.

Abstract In this paper we report on the results of a systematic study carried out on the fault and fracture systems exposed in the Majella Mountain, in the central Apennines fold and thrust belt of mainland Italy. The focus of our work was to assess the dimensional, spatial, and scaling properties of fault and fractures in carbonate rocks, in order to set up appropriate flow models for these types of potential geofluid reservoirs. The results provide information on (1) orientation, size distribution, density variations, and fractal characteristics of the fault and fracture networks affecting the Majella anticline; (2) the scaling properties and the overall architecture of different fault zone components; (3) the overprinting relationships between fault and fracture sets and the Majella fold structure. These data were used to elaborate a three-dimensional discrete fault and fracture model (DFFN model) of a ∼100 m3 geological volume, and for this to (1) evaluate the transport and storage properties of the reservoir; and (2) assess the degree of vulnerability and any possible hazard related to the exploitation and management of geofluids hosted in carbonate rock volumes.

Two independent active faults, capable of generating medium-sized earthquakes in the San Vito to Capo peninsula, northwestern Sicily (Italy) have been identified as a result of detailed field studies. In western Sicily, instrumental seismicity is low; in fact, except for the 1968 Belice earthquake (Ms = 5.4), historical records indicate that this area is relatively quiescent. Most of the seismicity is in the offshore sector of the Sicilian Maghrebian Chain, which is characterized by several medium- to low-magnitude events. The main shock of the 2002 Palermo seismic sequence (Mw = 5.9) represents the largest earthquake felt in the area in recent years. The deformation pattern characterizing the most recent faults mapped in northwestern Sicily includes a grid of high-angle faults consisting of major east-west-striking right-lateral and north-south-striking left-lateral features. This fault grid is related to a regional transcurrent right-lateral shear zone, here named the UEKA shear zone, bounded to the north by the Ustica-Eolie fault and to the south by the Kumeta-Alcantara fault. The UEKA shear zone accommodates the regional strain induced by the current stress field acting in the area, which, as emerges from both structural and seismological data, is characterized by a NW-SE-striking main compression.

In this paper we document deformation processes in porous carbonate grainstones of Cretaceous age in Majella Mountain in the central Apennines of Italy by detailed mapping of meso- and microstructural features as well as thin section observations and image analyses. We distinguished three main deformation mechanisms: (i) deformation bands developed by compaction and shear strain localization, (ii) stylolites formed by pressure solution, and (iii) subsequent shearing of stylolites. The deformation bands occur in six sets: five sets are compactive shear bands at high angles to bedding and one, which is the oldest, occurs parallel to bedding and is interpreted to be a compaction band. Stylolites localize along and within all six sets of deformation bands and are commonly sheared, as evidenced by striated surfaces and detectable offsets. These sheared stylolites are in many cases associated with one or two sets of subsidiary stylolites, oblique to the major set. The band-parallel sheared stylolites, together with the associated oblique sets of stylolites, form a tabular zone of fine grained cataclastic material within the compactive shear bands and accommodate slip in the range of 5-75 cm.The bed-parallel compaction bands and bed-parallel stylolites, which are kinematically compatible, are interpreted to be pre-tilting structures developed in response to the overburden, whereas the five sets of compactive shear bands and the associated stylolites and sheared stylolites likely occurred during the syn- and post-tilting deformation phases recorded in the Majella anticline. (C) 2006 Elsevier Ltd. All rights reserved.

Fault data from the central Apennines (Italy) were integrated with earthquake information from seismic catalogues in order to derive an empirical relation between the magnitude of the strongest historical earthquake and the fractal dimension of active fault patterns. We show that the assessment of earthquake magnitude from fault data has given good results, hence suggesting that the relation may be used to evaluate the potential hazard of seismic source areas in the Apennines using a low-cost methodology. We also suggest that a similar approach may be used in other seismic belts worldwide, provided that the basic seismological and geological information needed is adequate to constrain the appropriate relation between these two size parameters.

In the Earth sciences, the concept of fractals and scale invariance is well recognized in many natural objects. However, the use of fractals for spatial and temporal analyses of natural hazards has been less used (and accepted) in the Earth sciences. This book brings together 12 contributions that emphasize the role of fractal analyses in natural hazard research, including andslides, wildfires, floods, catastrophic rock fractures and earthquakes. A wide variety of spatial and temporal fractal-related approaches and techniques are applied to ‘natural’ data, experimental data and computer simulations. These approaches include probabilistic hazard analysis, cellular-automata models, spatial analyses, temporal variability, prediction and self-organizing behaviour. The main aims of this volume are (a) to present current research on fractal analyses as applied to natural hazards and (b) to stimulate the curiosity of advanced Earth science students and researchers in the use of fractals analyses for the better understanding of natural hazards.

We present here some new evidence for the occurrence of both right-lateral and left-lateral motion along the Mattinata Fault System (MAFS), a seismogenic structure in the southern sector of the Gargano promontory (Apulia, southern Italy). Right-lateral motion along the MAFS is recorded by geomorphic and structural features which suggest that dextral shear characterizes the most recent kinematic behaviour of the structure. Earlier left-lateral motion along the MAFS has been inferred mainly from the occurrence of localized pervasive pressure solution surfaces that are consistent with sinistral shear and by the presence of the Pantano di Sant' Egidio pull-apart, located in the left-stepping overlap zone between two major fault segments of the MAFS.Observed displacement values and computed slip-rates also allowed us to estimate, for the late dextral motion along the MAFS, a chronological interval of activity which is not less than 200 ka. (c) 2005 Elsevier Ltd. All rights reserved.

The Sila Grande Massif (SGM), in the northern sector of the Calabrian Arc, consists of a thrust-pile of metamorphic and non-metamorphic Paleozoic rocks (Fig. 1). The most representative tectonics structures of this area are NW-trending high angle faults, characterized by oblique transpressive and transtensional cinematics, which acted since middle Miocene (Van Dijk et al., 2000). Regionally, the definition of their activity was derived from the evolution of complex basin-margins, along which transtensional and transpressional faulting dominated (i.e. the Crotone Basin; Van Dijk, 1994).

Abstract The processes of brittle-ductile shear zone evolution and fault initiation by the coalescence of en echelon arrays of tensile cracks are quantitatively analysed in terms of displacement and temperature conditions at which they took place in very low-grade, well bedded micritic limestones from the southern Apennines, Italy. Three different types of structures are distinguished: (i) conjugate arrays of en echelon, calcite-filled tension gashes, showing extensional shear offsets; (ii) en echelon vein arrays showing incipient development of discontinuous shear-parallel fractures cutting through the tension gashes; and (iii) faulted vein arrays, in which vein array breaching by a continuous, discrete normal fault has occurred. Fluid inclusion microthermometry from vein calcite sampled from the different sets of structures (i) to (iii) above indicates that environmental conditions remained roughly constant during the different stages of vein array evolution and fault development, with average homogenization temperatures from primary fluid inclusions being in the range 130–140°C. Our results show how displacement accumulation and shear strain essentially control vein array evolution by rotation of en echelon tension gashes, fracture linkage and, eventually, fault nucleation, at approximately constant temperature.

The study of some major fault zones in the Apennines was mostly focused on the acquisition of quantitative data in situ aimed at deriving input parameters for modelling faulted rock volumes. Structural data collected in the Monte Alpi area (southern Italy) and in the central Apennines allowed us to: (i) estimate the fractal dimension characterizing the geometric complexity and size distribution of different fault and fracture patterns; (ii) assess the appropriate parameters defining the overall architecture, anisotropy and related permeability structure of the mapped fault zones; and (iii) constrain the scaling properties of some of the attributes (i.e. length, spacing, map pattern, fracture density, etc.) of both fault-related and regional fracture sets.The results of our work suggest that the above data are appropriate for extrapolating field based information at different scales, and for producing 3D models of fault and fracture networks.

In this paper we illustrate the state of the art of the European Co-operation in the Field of Scientific and Technical Research, COST Action 625 “3-D Monitoring of Active Tectonic Structures” in Italy. The project is mainly focused on detecting strain variations and/or any phenomena that may precede future seismic events, in order to evaluate the time evolution and modes of deformation of seismogenic structures during the inter-coseismic cycles. We selected two note seismic areas, (i) the Gargano promontory (southern Italy) and (ii) the Norcia basin (central Italy), for the installation of a monitoring equipment consisting of: (a) local networks of geodetic stations (benchmark for GPS and total station measurements with micrometric sensitivity) and (b) 3D monitoring devices (TM71; capable of recording micrometric displacements). In this paper we show the geo-structural analysis and detailed morphostructural studies, including high-resolution seismic reflection profiles and paleoseismological investigations, carried out across the main active faults of selected areas, which allowed us to assess the main spatial and dimensional properties of faults. As concerns the monitoring experiment, available data are not yet adequate to be used for convincing tectonic interpretations because the installation of local GPS stations and that of TM71 extensometers has been carried out only very recently. Accordingly, we only show a few examples of microdisplacement measurements carried out in both areas.

A variety of models show that crustal deformation is a self-organized process on long (geologic) timescales. In this paper, we analyse an active seismogenic crustal-scale fault system (the Central Apennines Fault System or CAFS) with the aim of assessing the spatial and temporal characteristics of fault development and related earthquake activity. The basic properties of the CAFS, as derived from our study, are then compared with those of other fault systems worldwide in order to validate/constrain the results of available statistical physics models based on self organized criticality (SOC).

The 1857 Basilicata earthquake (Imax=XI° MCS; Me=6.9) is one of the most destructive events that occurred in peninsular Italy; shaking effects and ground breaks were recorded over a large area extending from the Vallo di Diano (Campania) to the Val d'Agri (Basilicata) for a length of about 60 km and with a width of more than 10 km. Within this seismogenic belt, only another strong earthquake, with maximum intensities in the range of X° MCS (Me=6.4), occurred in 1561. In the epicentral area of the 1857 earthquake, two regional fault systems (i.e. the Val d'Agri and the Vallo di Diano fault systems) offset the main features of the southern Apennines fold and thrust belt; both systems show evidence of activity during Pleistocene times. The Vallo di Diano Fault System (DIFS) includes mostly NW–SE and WNW–ESE trending faults displaying long-term displacements of a few hundred meters; slip data from the latter faults record a kinematic transition from almost pure normal motion to dextral/oblique motion, whereas the NW–SE oriented faults are mostly dominated by normal/transtensional (sinistral) motion. The Val d'Agri Fault System (VAFS) is characterized by fault zones of different size; it is a kinematically coherent system including roughly N120° trending left-lateral strike-slip faults and N090°–N100° trending left-lateral transtensional faults. Inversion of fault slip data indicates that the stress field conditions responsible for the genesis and evolution of the two fault systems are quite different, with σ1 being: (1) sub-horizontal and WSW–ENE trending, in the case of the VAFS, and (2) sub-vertical, in the case of the DIFS. However, the two fault systems are characterized by a roughly N–S oriented extension, and by R-values indicating that σ1≌σ2>>σ3. This suggests the possibility that, in these areas, permutations between the principal maximum and intermediate axes of the stress ellipsoid may have frequently occurred during the faulting process. In this paper, we present new data for both the VAFS and DIFS and discuss the inferred modes of interaction between the two fault systems; this, in turn, suggests possible implications for seismic hazard analyses (SHA) in this sector of the southern Apennines.

Thrust propagation through previously faulted continental margins may result in fold and thrust belts whose structure is strongly controlled by the inherited basin archi- tecture. A detailed geological study has been carried out in the external zone of the Umbria-Marche Apennines, from Monte San Vicino to the north, to Montagna dei Fiori to the south. Stratigraphic and structural data, together with the construction of a series of balanced and restored geological sections, point out the fundamental role played by the pre- orogenic basin architecture in controlling the geometry and evolution of the fold and thrust belt. Pre-thrusting structures include not only those inherited from the Mesozoic rifted continental margin, but also synsedimentary faults associated with Miocene extension which occurred ahead of the advanc- ing thrust front. The latter structures produced important fa- cies and thickness variations in the units deposited during the late Burdigalian-early Messinian, pre-evaporitic stages of foredeep development. In the southern sector (Montagna dei Fiori), high values of Messinian regional subsidence, bathymetry and sedimentation rate overcome the effects of synsedimentary extensional tectonics, which is best recorded in pre-Messinian sequences. On the other hand, Messinian regional subsidence was significantly less in the northern sec- tor (Monte San Vicino). Here, several minor sub-basins de- veloped within the foredeep, generally reaching evaporitic conditions during the middle Messinian (marked by the de- position of the Gessoso-solfifera Fm). In this area, a ma- jor control by pre-thrusting normal faults on sedimentation is recorded in the foredeep siliciclastic sequences. Late Burdigalian-early Messinian extension, possibly associated with flexure of the foreland lithosphere, peripheral bulge up- lift and/or foreland tectonic activity, was followed by a late Messinian (post-evaporitic) contractional episode of regional extent. During shortening, inversion of preexisting Miocene

Thrust propagation through previously rifted continental margins may result in fold and thrust belts whose structure is strongly controlled by the inherited basin architecture, as it occurs in southern Italy. The Lagonegro units of the southern Apennines comprise a deformed pelagic basin succession showing variable stratigraphic characteristics, mainly lateral variations in both facies and thickness, interpreted to be due to a complex basin topography related to a Triassic rifting event. In contrast to previous studies, cross-section balancing and restoration indicate that the Lagonegro units exposed in the high Agri Valley area suffered relatively limited internal shortening (8 km, i.e. 35%). Early deformation of these rocks, later incorporated into a large-displacement thrust sheet, was dominated by folding around (present-day) roughly north–south-trending axes. The attainment of a regional décollement level was favoured by an early mild inversion of the basin, producing a roughly similar structural elevation of both hanging-wall and footwall successions to Mesozoic faults. Most of the contractional deformation was accommodated by buckling of the Mesozoic syn-rift strata between synsedimentary faults, which represented major mechanical interfaces. Early strain localization in the Lagonegro Basin ahead of the active thrust front was most probably mechanically controlled by a faulted crustal segment which originally lay, within the continental margin, between two massive carbonate platforms.

The study of Quaternary fault zones in the High Agri Valley (southern Italy) and in the axial zones of the central Apennines, allowed us to collect information on the permeability structure, fluid characteristics, and scaling properties of the main fault zones exposed in the area.Detailed structural mapping allowed us to derive the appropriate values of the fractal dimension characterising different active fault zone patterns and to evaluate the basic parameters needed for assessing the architecture and related permeability structure of the mapped faults. Scan line and scan area analysis helped in constraining the scaling properties of some of the attributes (i.e. fault zone thickness, fracture spacing etc.) of the main fault zones and in defining their validity range. Our results suggest that, in the Apennines, (i) extrapolation of the architectural indices of a fault zone is admissible over three orders of magnitude, and (ii) the composition of the analysed fluid inclusions and related homogenisation temperatures are associated with fault-driven fluid circulation from both superficial and deep (4-6 km) levels. (C) 2001 Elsevier Science B.V. All rights reserved.

In this paper we present the results of a geostructural study on active faults in central Italy, where seismogenic fault zones occur as part of a Quaternary network dissecting and/or inverting earlier tectonic features of the central Apennines fold and thrust belt. In our work we focus on the possibility of using structurally-oriented quantitative analysis of fault fabrics and fluid inclusion studies for assessing the hydraulic properties and scaling relations of fault zones in order to evaluate the role and effects of the interaction between rock and fluids in the brittle deformation of strained crustal rock volumes. The results of our study show that this approach is appropriate for (i) assessing the structural permeability of faulted and fractured rock volumes, (ii) defining the conduit/barrier behaviour of fault zones to fluid flow, (iii) mapping spatial variations of the fluid pressure across different fault segments, (iv) evaluating the maturity of a structural network and the degree of interaction of linked structural discontinuities, (v) assessing fluid composition and the conditions of deformation by means of microstructural and fluid inclusion data.