Active Tectonics in the Central Apennines (Italy) – Input Data for Seismic Hazard Assessment

Quaternary tectonics and paleoseismologicalinvestigations have defined a reliable framework ofactive faults in the southern Umbria and AbruzziApennines. Two sets of NW–SE to NNW–SSE trending, 16to 33 km-long, normal and normal-oblique faults orfault systems have caused the displacement of LatePleistocene–Holocene deposits and landforms within theinvestigated sector. Available data on verticaloffsets indicate that both Late Pleistocene–Holoceneand Quaternary (since the later part of the EarlyPleistocene; 0.9–1 Ma) slip rates range between 0.4and 1.2 mm/yr (range 0.6–0.8 mm/yr preferred).Paleoseismological investigations show that recurrenceintervals for surface faulting events are alwaysgreater than 1,000 years and are usually greater than2,000 years. Both paleoseismological data andlong-term seismicity show that activation of theinvestigated faults may result in earthquakes ofM = 6.5–7.0. The extension rate across the two sets ofprimary faults ranges between 0.7 and 1.6 mm/yr.Horizontal seismic strain has been calculated to be0.5–0.6 mm/yr, based on the summation of the seismicmoment of M > 5.3 earthquakes which have affected theinvestigated area since 1200 AD. This value may belower than that inferred through geological data,probably because the seismological record reliable forthe addition of the seismic moments covers a too shorttime window (about 800 years) to be consideredrepresentative of the tectonic activity in theinvestigated area. This conclusion iscorroborated by the large recurrence intervalper fault (>1,000–2,000 years) inferred frompaleoseismological analysis. A comparison of theactive-fault framework and historical-seismicitydistribution indicates that the entire eastern set ofactive faults has likely not been activated since 1000AD, thus indicating that the elapsed time since thelast activation for several faults of the investigatedarea may be greater than 1,000 years. In terms ofhazard, the highest probability of activation isrelated to the eastern set faults, due to theobservation that the elapsed time for some of thesefaults may be similar to the recurrence interval. Asan example, paleoseismological andarchaeoseismological data indicate that the elapsedtime for the Mt. Vettore and Mt. Morrone Faults may begreater than 1,650 and 1,850 years, respectively.These data may have significant implications for riskrelated to a number of towns in central Italy and tothe city of Rome. As for the latter, in fact,monumental heritage has suffered significant damagedue to earthquakes of M > 6.5 which originated in theinvestigated Apennine sector.     

New data for the kinematic interpretation of the Alps–Apennines junction (Northwestern Italy)

Alps and Apennines are juxtaposed within an approximately 100 km-wide area covered by the Upper Eocene to Miocene successions of the Tertiary Piedmont Basin. The Upper Eocene–Oligocene evolution of this area was characterized to the north and west by the propagation of the SE-verging Southalpine thrust-fold belt that can be traced from the Po Plain subsurface until the Torino Hill-Saluzzese area, and to the south by a high-angle, broadly E–W oriented megashear zone that led to the juxtaposition of different crustal levels and controlled the development of a mosaic of partly independent sub-basins. Since the latest Oligocene the N-verging Apenninic tectonics prevailed in the collisional system and the Tertiary Piedmont Basin evolved as a wide thrust-top basin, bounded to the north by the N-verging Monferrato arc and characterized by a tectono-sedimentary evolution recording changes of subsidence and shift of depocentres in relation to crustal structures.     

Landform classification: a high-performing mapping unit partitioning tool for landslide susceptibility assessment—a test in the Imera River basin (northern Sicily,Italy)

In landslide susceptibility studies, the type of mapping unit adopted affects the obtained models and maps in terms of accuracy, robustness, spatial resolution and geomorphological adequacy. To evaluate the optimal selection of these units, a test has been carried out in an important catchment of northern Sicily (the Imera River basin), where the spatial relationships between a set of predictors and an inventory of 1608 rotational/translational landslides were analysed using the multivariate adaptive regression splines (MARS) method. In particular, landslide susceptibility models were prepared and compared by adopting four different types of mapping units: the largely adopted grid cells (PX), the typical contributing area–controlled slope units (5000_SLU), the recently optimized parameter-free multiscale slope units (PF_SLU) and a new type (LCL_SLU) of slope unit obtained by crossing classic hydrological partitioning with landform classification. At the same time, once a pixel-based model was prepared, four different SLU modelling strategies were applied to each of the obtained slope unit layers, including two different types of pixel score zoning, a pixel score re-modelling and a factor-based SLU re-modelling. According to the achieved results, LCL_SLUs produced the highest performance and reliability, offering an optimal compromise between the high-performing but scattered and the smoothed but lower-performing prediction images that were obtained from pixel-based and hydrologic SLU–based modelling, respectively. Additionally, among the four adopted SLU modelling strategies, the new proposed procedure, which uses the zoned pixel–based score deciles as the LCL_SLU predictors for a new regression, resulted in the best outstanding performance (ROC_AUC?=?0.95).

     

Tephrochronological study in the quaternary Val d’Agri intermontane basin (Southern Apennines,Italy)

In the south-eastern depocentre of the Val d’Agri basin (Southern Apennines), a volcanic ash layer crops out interbedded within poorly structured alluvial fan deposits of Late Pleistocene age. Textural, depositional and pedological features of this weathered layer suggest a primary deposition from a pyroclastic fall-out of volcanic ash. Chemical analyses of feldspars show an alkali trachytic composition and accessory minerals association allow to correlate this tephra layer with the regionally dispersed Y-7 marine tephra layer (Tufo Verde Epomeo eruption, Ischia volcano), dated at 56 ± 4 ka. The Val d’Agri tephra here described for the first time was deposited during MIS Stage 3. Its recovery and characterization permit to contribute to regional correlation of the Mediterranean climatic and volcanic events from marine to continental successions and to describe landscape evolution of the Southern Apennines during glacial–interglacial cycles.     

Upper crust “boudinage” during post-collisional Miocene extension in Tuscany: Insights from the southern part of the Larderello geothermal area (Northern Apennines,Italy)

A geological study carried out in the southern part of the Larderello geothermal area (Northern Apennines) provides new information on the development mechanism and timing of the earlier extensional structures that formed during the Miocene post-collisional tectonics which affected the orogen. Staircase low-angle normal faults (LANFs) affected a multilayered thickened upper crust after the collisional stage, producing the lateral segmentation of the Tuscan Nappe, the deeper non-metamorphic tectonic unit of the Northern Apennines in the Tuscan area. The tectonic history recorded in two Tuscan Nappe discontinuous bodies revealed that the LANFs took place during the Middle–Late Miocene, displacing collisional structures developed from the Late Oligocene. These Tuscan Nappe bodies are delimited by detachment faults located at the base, within the Tuscan evaporites, and at the top within the Ligurian Units. Their western and eastern margins coincide with east-dipping ramps. These structures and the Tuscan Nappe bodies were later dissected by Pliocene–Quaternary high-angle normal faults. The reconstructed deformation history implies that the Tuscan Nappe bodies are extensional horses developed through an earlier asymmetrical east-dipping extensional duplex system, involved in block faulting during the later, Pliocene-Quaternary, stage of extension.     

Metamorphic consequences of Neogene thermal anomaly in the northern Apennines (Radicondoli-Travale area,Larderello geothermal field – Italy)

Abstract

In the Radicondoli–Travale area of the Larderello geothermal field (Italy) new structural and petrologic data on some metamorphic units, cored from geothermal wells, reveal the existence of a wide complex of hornfels rocks. The development of the complex is related to the emplacement of Neogene magmatic rocks at a shallow depth within a Permo–Triassic terrigenous metasedimentary sequence of a low metamorphic grade. The sequence was subjected to alpine tectonic-metamorphic events. This reconstruction gives new insights in the tectonic setting of metamorphic units below the Tuscan Nappe, in southern Tuscany. Particularly, the medium and high grade metamorphic rocks seem strictly related to the development of Neogene thermal aureoles and do not represent remnants of a Paleozoic basement. Furthermore, in this sector of the Larderello geothermal system, the presence of deep geothermal reservoir at a depth of 3 000 m is mainly linked to the enhanced permeability caused by fracturing in these hornfels rocks. This fracturing is a consequence of the dehydration reaction occurring in the metapelites due to Neogene thermal metamorphism. This mechanism allowed the development of a long-lived hydrothermal system, shown by the secondary mineralogical assemblages. These testify the presence of at least two hydrothermal stages which are well preserved in the less permeable units. © 2000 Editions scientifiques et médicales Elsevier SAS     

Metamorphic consequences of Neogene thermal anomaly in the northern Apennines (Radicondoli-Travale area,Larderello geothermal field – Italy)

In the Radicondoli–Travale area of the Larderello geothermal field (Italy) new structural and petrologic data on some metamorphic units, cored from geothermal wells, reveal the existence of a wide complex of hornfels rocks. The development of the complex is related to the emplacement of Neogene magmatic rocks at a shallow depth within a Permo–Triassic terrigenous metasedimentary sequence of a low metamorphic grade. The sequence was subjected to alpine tectonic-metamorphic events. This reconstruction gives new insights in the tectonic setting of metamorphic units below the Tuscan Nappe, in southern Tuscany. Particularly, the medium and high grade metamorphic rocks seem strictly related to the development of Neogene thermal aureoles and do not represent remnants of a Paleozoic basement. Furthermore, in this sector of the Larderello geothermal system, the presence of deep geothermal reservoir at a depth of 3 000 m is mainly linked to the enhanced permeability caused by fracturing in these hornfels rocks. This fracturing is a consequence of the dehydration reaction occurring in the metapelites due to Neogene thermal metamorphism. This mechanism allowed the development of a long-lived hydrothermal system, shown by the secondary mineralogical assemblages. These testify the presence of at least two hydrothermal stages which are well preserved in the less permeable units.     

Land-use planning for natural hazards in New Zealand: the setting,barriers, ‘burning issues’ and priority actions

Land-use planners have a critical role to play in building vibrant, sustainable and hazard resilient communities in New Zealand. The policy and legal setting for natural hazards planning provides a solid foundation for good practice. But there are many examples of ‘bad practice’ that result in unnecessary risks and, in some cases, exposure to repeat events and potentially devastating impacts. Much, therefore, remains to be done to improve hazards planning policy and practice in New Zealand. This article explores the questions: What role does land-use planning play in managing hazard risks in New Zealand; and what needs to be done to reduce hazard risks and build community resilience? The article starts by describing the milieu within which natural hazards planning takes place. It goes onto outline the stakeholders and institutional and legal setting for natural hazards planning in New Zealand, including barriers to realising the potential of natural hazards planning. This synthesis reveals a number of ‘burning issues’, including the need to: (a) Improve understanding about the nature of hazards; (b) Prioritise risk avoidance (reduction) measures; (c) Provide national guidance for communities exposed to repeat events and address the relocation issue and (d) Mainstream climate change adaptation. Each ‘burning issue’ is discussed, and priority actions are recommended to realise the potential of land-use planning to reduce natural hazard risks and build community resilience in New Zealand. Ultimately, the challenge is to develop a cooperative hazards governance approach that is founded on coordinated policies, laws and institutions, cooperative professional practice and collaborative communities.     

Retrogressive fabric development during exhumation of the Voltri Massif (Ligurian Alps,Italy): arguments for an extensional origin and implications for the Alps–Apennines linkage

Geological mapping coupled with structural investigations carried out in the Voltri Massif (eastern Ligurian Alps, Italy) provide new data for the interpretation of the tectonic context controlling main fabric development during exhumation of its high-pressure core. The Voltri Massif is here interpreted as a c. 30 km-long eclogite-bearing, asymmetric dome formed by the progressive verticalisation of the regional, second-phase mylonitic foliation developed during retrogressive greenschist metamorphic conditions. In this light, the exhumation history is driven by a ductile-to-brittle extensional process, operating through low-angle, top-to-the-W multiple detachment systems. A Late Eocene–Early Oligocene age for this extensional episode is proposed on the basis of structural correlations, stratigraphic and radiometric constraints. In this scenario, the Voltri Massif is interpreted as an extensional domain developed to accommodate the Late Eocene–Early Oligocene arching of the Western Alps–Northern Apennines orogenic system.     

Formation of helictite in the cave Dragon Belly (Sardinia,Italy)—Microstructure and incorporation of Mg,Sr, and Ba

In the Dragon Belly cave helictites, a special type of irregular speleothem, are found, which grew on stalactites in all vertical and horizontal directions without any affinity to gravity. Microstructural and mineralogical analyses of this stalactite–helictite system indicate that its evolution is initiated by clogging of the central stalactite channel at its tip, probably when the cave was flooded by muddy water. Clogging caused the formation of secondary channels (≈0.2 mm in diameter) for water passage through the outer surface of the stalactite, where helictites start to grow. The secondary channel passes into the central channel of the helictite.The helictites consist of stacked idiomorphic calcite crystals with uniform orientation. Growth of calcite is essentially controlled by water transfer through the central channel and via canalicules (narrow channels of ≈0.05 mm in diameter) following the crystal boundaries of the calcite mesocrystal induced by capillary hydrostatic forces. At straight parts of the helictites calcite crystals are almost uniform in size, but at bended parts crystals are significantly smaller inside (≤0.1 mm in length) than outside of the bend (≤0.5 mm). It is proposed that the difference in calcite volume (larger crystals) vs. the inside of the bend leads to a helix form, which explains the origin of the term helictite.The Sr and Ba concentrations measured by laser ablation along helictites can be explained by cation incorporation during calcite precipitation close to equilibrium. Dilution effects caused by seasonality control the elemental distribution in the helictite, which result in a positive correlation between Sr and Ba. Variability of Mg is unrelated with Sr and Ba, and is probably due to the incongruent dissolution of Mg–calcite from the host rock.     

Mafic rocks in a deep-crustal segment of the Variscides (the Góry Sowie, SW Poland): evidence for crustal contamination in an extensional setting

Coronitic metagabbronorites (so-called hyperites) and metabasites occur within gneisses, migmatites and minor granulites in the high-grade metamorphic Góry Sowie Block in the Sudetes (SW Poland). Incompatible trace-element and )Nd data, combined with field and petrographic evidence, suggest that three groups may be distinguished: (1) "enriched" amphibolites (Zr/Nb ca. 8, )Nd₅₀₀ +1 - +2.5), (2) "depleted" amphibolites (Zr/Nb >30, )Nd₅₀₀ +5 - +6), and (3) metagabbronorites (Zr/Nb 13-19, )Nd₅₀₀ scattered between +5.3 and -1). These characteristics favour an extensional within-plate setting, consistent with their field occurrence as small bodies scattered within metasedimentary and felsic metaigneous gneisses. In that setting, enriched mantle sources were partially melted to produce a range of basic magmas, showing affinities with continental tholeiites (within plate-type basalts). Presumably, in a more advanced stage of rifting, more depleted varieties, transitional to N-MORB, were emplaced. These mafic magmas were variably contaminated during their ascent in the crust. The metagabbronorites, with their well-preserved igneous textures, were previously interpreted as having been intruded after the main deformation and after the peak of amphibolite facies metamorphism (some authors suggesting a relation to the "circum Góry Sowie ophiolites"). However, the geochemical characteristics and P-T estimates suggest that the metagabbronorites are unrelated to the ophiolitic gabbros found in the neighbourhood of the Góry Sowie Block and, in contrast to them, have experienced a complex, polybaric P-T path.     

Ground penetrating radar survey finalized to the recovery of the “S. Agata alla Badia” church in Catania (eastern Sicily,Italy)

Numerous archaeological sites dating to the greek-roman period have been found in the underground of the city of Catania (eastern Sicily, Italy). Their presence is a testimony of the several settlements that have followed in this area over time. In this work we have conducted electromagnetic surveys, consisting of ten georadar profiles, inside the church of “S. Agata alla Badia”, damaged during the earthquake occurred in eastern Sicily on 13 December 1990. The aim was to investigate the area where the church is located to obtain information useful for its structural recovery. Mechanical drillings were also carried out to reconstruct the local stratigraphy, which could be complicated by the presence of underground cavities and artefacts, as evidenced by recent excavations beneath the Catania Cathedral, in the nearby Piazza Duomo. From the interpretation of the GPR data, the presence of ancient masonry structures underlying the recent foundations was highlighted. In addition, the GPR survey allowed us to identify and locate reflective horizons in the subsurface, probably due to the presence of materials with different state of aggregation and/or to buried structures.     

The Corsica–Sardinia Massif as source area for the early northern Apennines foredeep system: evidence from debris flows in the "Macigno costiero" (Late Oligocene, Italy)

Large isolated gravity flows (debrites) are widely present in the stratigraphic record of the northern Apennines foreland-basin system. These strata may be useful for provenance signals and dispersal pathways during foreland evolution. This paper examines a cohesive debris flow bed interbedded with turbidite strata of the Macigno Formation (Late Oligocene, Tuscany, Italy), in order to obtain new data on the provenance of the clastic material. Clasts in the debris flow are predominantly plutonic (granodiorite, tonalite, and S-granite) and subordinately metamorphic (gneiss and schist) and sedimentary calcareous clasts. The composition of the clasts within the debris flow is similar to the clastic composition of the interbedded turbidite sandstones of the "Macigno costiero." The depositional features of the debris flow suggest that it traveled for a short distance within the basin before it was deposited not far from the slope. The absence of a high-pressure/low-temperature (HP/LT) paragenesis in the plutonic and metamorphic clasts of the debris flow indicates a provenance from a crystalline basement not involved in the high-pressure phases of the Alpine Orogenesis. Previous studies have indicated the Central-Western Alps as potential source areas for the Macigno Formation sediments. The lack of HP/LT metamorphic signatures in our studied samples excludes the Pennidic and Austroalpine nappes of the Western Alps as possible sources for the debris flows of the "Macigno costiero." These new data (sedimentological, petrographical, and microstructural) suggest that the Corsica-Sardinia Hercynian basement, lacking a HP/LT paragenesis, is the more accredited source area of the debris flow and of the related turbidite sandstones of the "Macigno costiero" succession. These foredeep-feeding sediments were probably before deposited within an episutural basin developed close to the northern Apennines orogenic wedge.     

(Re)constructing rural–urban spaces: gendered livelihoods,migration, and natural resources in South Africa

Critical approaches to development theory and practice provide alternative perspectives that focus on counterhegemonic and discursive dimensions of the development process. Feminist development is one such approach that opens up new spaces and opportunities to promote socially progressive and sustainable economic strategies. This paper uses feminist development geography as a framework to highlight the intersection of diverse spaces and economic strategies at the household and community levels. The analysis focuses on gendered livelihoods that are linked to circular migration and use of natural resources as a way to understand the integration of rural and urban spaces of development. The empirical section of this paper examines demographic patterns and socio-economic trends in Limpopo Province, South Africa as a context for the case study of two community-based women’s producer groups. These examples illustrate how economic strategies and social identities are embedded in and integrate both rural and urban spaces. This analysis contributes to feminist and post-structural development theory and practice by highlighting the potential for progressive forms of economic and social empowerment.     

Role of slumped beds in the genesis and evolution of huge hypogean rooms: an example in the Valle del Nosê (Como,Northern Italy)

Abstract

During a detailed structural analysis of the cave systems of the Valle del Nosê (Como, Northern Italy), a systematic occurrence of thick (metric to decametric) slumped beds in several huge rooms and in other wide underground voids was observed. The systematic control, that these structures exert on the morphologies of the karst systems, suggests that slumped beds might play a major role in the genesis and evolution of large underground voids. In fact, thanks to their very high permeability, these beds seem to be able to act as the preferential way for water flowing in the very first phases of karst development, thus guiding cave development, while their mechanical properties, different from those of unslumped beds, make them prone to break down collapse, thus increasing the possibilities of the formation of huge rooms. On the basis of the observed field data, a genetic and evolutive model is therefore suggested to explain the origin of the largest voids in this area. This model has by now a strictly local effectiveness. © 2000 Éditions scientifiques et médicales Elsevier SAS     

Studying travertines for neotectonics investigations: Middle–Late Pleistocene syn-tectonic travertine deposition at Serre di Rapolano (Northern Apennines, Italy)

Middle–Late Pleistocene tectonic activity has been inferred through studies on travertine deposits exposed in a tract of the hinterland Northern Apennines. A detailed study on the relationships between tectonics and travertine deposition coupled with ²³⁰Th/²³⁴U age determination of travertines at Cava Oliviera quarry, located close to Serre di Rapolano village (southern Tuscany, Northern Apennines), allowed us to recognise Pleistocene faults, whose activity has been referred to 157–24 ka, at least. Travertine deposition was tectonically controlled by WSW-ENE striking, oblique and normal faults, associated to a main fault (named as the Violante Fault). This structure dissected a regional normal fault (known as the Rapolano Fault) Early–Middle Pliocene in age, which bounded the eastern side of the Pliocene Siena Basin, and gave rise to space accommodation for clayey and sandy marine sediments. Hydrothermal circulation (and related travertine deposition) was favoured by the damaging enhancement due to the fault–fault intersection. Tectonic activity has been also documented by deformation recorded by travertines, which suggest a main tectonic event between 64 ± 5 and 40 ± 5 ka. The tectonic activity described for the study area agrees with the Quaternary tectonic evolution documented in the surrounding areas (e.g. Mt. Amiata and Mt. Vulsini), as well as the Tyrrhenian margin of the Central Apennines, indicating that a widespread tectonic activity affected the inner part of the Apennines until the latest Quaternary.     

Role of slumped beds in the genesis and evolution of huge hypogean rooms: an example in the Valle del Nosê (Como,Northern Italy)

During a detailed structural analysis of the cave systems of the Valle del Nosê (Como, Northern Italy), a systematic occurrence of thick (metric to decametric) slumped beds in several huge rooms and in other wide underground voids was observed. The systematic control, that these structures exert on the morphologies of the karst systems, suggests that slumped beds might play a major role in the genesis and evolution of large underground voids. In fact, thanks to their very high permeability, these beds seem to be able to act as the preferential way for water flowing in the very first phases of karst development, thus guiding cave development, while their mechanical properties, different from those of unslumped beds, make them prone to break down collapse, thus increasing the possibilities of the formation of huge rooms. On the basis of the observed field data, a genetic and evolutive model is therefore suggested to explain the origin of the largest voids in this area. This model has by now a strictly local effectiveness.     

Different types of fine-grained sediments associated with acid mine drainage in the Libiola Fe–Cu mine area (Ligurian Apennines,Italy)

Different types of fine-grained chemical precipitates were characterized in the surroundings of the pyrite-chalcopyrite mine of Libiola (Northern Italy). Both water chemistry and sediment composition were used to investigate metal mobility near the mine area. Local drainage waters were very acidic (with a pH as low as 2.5) and were rich in dissolved metals (Fe, Al, Cu, Zn, Mn, Ni). Sediments associated with low pH water (pH <4.5) were ochreous mixtures of schwertmannite and goethite with traces of jarosite. Their chemistry was dominated by Fe and they had, compared to other sediments investigated, low concentrations of other metals. When the acidity decreased gradually, other precipitates formed. At a pH of approximately 5, a poorly crystalline, whitish, Al-rich precipitate occurred. At a pH between 6 and 7, a poorly crystalline, blue, Cu (Zn) rich phase was present. These “sequential” precipitation events progressively reduced the metal loading typical of the acidic mine water when there was a gradual mixing with normal water. When a sudden mixing between normal waters (pH ∼8, Ca–HCO₃, low metal bearing) and acidic waters took place, a rapid flocculation occurred of mixed precipitates containing Fe, Al and trace elements.     

Seismotectonic versus man-induced morphological changes in a cave on the Arrábida chain (Portugal)

Abstract

Distinctions between cave morphologies originating from seismic or active tectonics and those generated by natural clastic breakdown or by human activity must be made using unambiguous interpretative criteria.

Easily accessible caves in particular, which may have been visited for centuries or millennia, or caves located near engineering works or quarries using great quantities of explosives, may have broken speleothems, breakdowns or detachment joints unrelated to seismic events or tectonic movements.

Zambujal cave lies near neotectonic and seismic structures associated with a Plio-Quatemary 200 m uplift of the Arrábida chain and has suffered impacts resulting from quarrying, followed by possible vandalism. It is thus an example for which it is difficult to decipher morphological agents as there is the possibility that identical forms have been generated by several causes, which may have repeated at different episodes of its evolution. However, a careful morphological interpretation makes it possible to accept the existence of two seismic episodes, an “ancient” one and a “modern” one. The detection of other episodes between these is only possible using absolute dating. © Elsevier, Paris