Geodynamic evolution of ophiolites from Albania and Greece (Dinaric-Hellenic belt): one, two, or more oceanic basins?

All the geological constraints for an exhaustive reconstruction of the Triassic to Tertiary tectonic history of the southern Dinaric-Hellenic belt can be found in Albania and Greece. This article aims to schematically reconstruct this long tectonic evolution primarily based on a detailed analysis of the tectonic setting, the stratigraphy, the geochemistry, and the age of the ophiolites. In contrast to what was previously reported in the literature, we propose a new subdivision on a regional scale of the ophiolite complexes cropping out in Albania and Greece. This new subdivision includes six types of ophiolite occurrences, each corresponding to different tectonic units derived from a single obducted sheet. These units are represented by: (1) sub-ophiolite mélange, (2) Triassic ocean-floor ophiolites, (3) metamorphic soles, (4) Jurassic fore-arc ophiolites, (5) Jurassic intra-oceanic-arc ophiolites, and (6) Jurassic back-arc basin ophiolites. The overall features of these ophiolites are coherent with the existence of a single, though composite, oceanic basin located east of the Adria/Pelagonian continental margin. This oceanic basin was originated during the Middle Triassic and was subsequently (Early Jurassic) affected by an east-dipping intra-oceanic subduction. This subduction was responsible for the birth of intra-oceanic-arc and back-arc oceanic basins separated by a continental volcanic arc during the Early to Middle Jurassic. From the uppermost Middle Jurassic to the Early Cretaceous, an obduction developed, during which the ophiolites were thrust westwards firstly onto the neighboring oceanic lithosphere and then onto the Adria margin.     

Impact of the magnitude and frequency of debris‐flow events on the evolution of an alpine alluvial fan during the last two centuries: responses to natural and anthropogenic controls

The dynamics and the surface evolution of a post‐LGM debris‐flow‐dominated alluvial fan (Tartano alluvial fan), which lies on the floor of an alpine valley (Valtellina, Northern Italy), have been investigated by means of an integrated study comprising geomorphological field work, a sedimentological study, photointerpretation, quantitative geomorphology, analysis of ancient to modern cartography and consultation of historical documents and records. The fan catchment meteoclimatic, geological and geomorphological characteristics result in fast rates of geomorphic reorganization of the fan surface (2 km²). The dynamics of the fan are determined by the alternation of low‐return period catastrophic alluvial events dominated by non‐cohesive debris flows triggered by extreme rainstorms which caused aggradation and steepening of the fan and avulsion of its main channel, with periods of low to moderate streamflow discharge punctuated by low‐ to intermediate‐magnitude flood events, causing slower but steady topographic reworking. The most ancient parts of the fan surface date back at least to the first half of the 19th century, but most of the fan surface has been restructured after 1911, mainly during the debris‐flow‐dominated events of 1911 and 1987. Phases of rapid fan toe incision and fan degradation have been recognized; since the 1930s or 1940s, the Tartano fan has been subjected to a state of deep entrenchment and narrowing of the main trunk channel and distributary area. Post‐Little Ice Age climate change and present‐day surface uplift rates have been considered as possible explanations for the observed geomorphic evolution, but tectonic or climatic controls cannot account for the order of magnitude of the erosional pace. Anthropogenic controls plausibly override the natural ones: in particular, the building of a dam in the late 1920s, about 2 km upstream of the fan, seems to have triggered fan dissection, having altered the sediment discharge through sediment retention. Copyright © 2011 John Wiley & Sons, Ltd.     

A novel insight into vertical ground motion modelling in earthquake engineering

Recent observations of failure and damage of buildings and structures under seismic action has led to an increasing interest for an in-depth analysis of the vertical component of site ground motion. In particular, when dealing with saturated soils, the current engineering practice does not usually go beyond the simplified $u$–$p$ formulation of the Biot's equations describing the coupled hydro-mechanical behaviour, thus neglecting some terms of fluid inertial forces, despite the presence of more refined formulations, for example, the $u$–$U$ formulation. Therefore, a theoretical and numerical validation of the $u$–$p$ formulation as compared with the $u$–$U$ formulation is proposed in this work, where the numerical simulations are compared with the analytical solution for the $u$–$p$ formulation, which is also derived and illustrated in this text. The comparison between the two formulations and the analytical solution is provided for different levels of permeability and dynamic actions, which are representative of a wide scenario of site ground properties and seismic hazard in the vertical direction. In particular, the soil response is analysed in terms of acceleration and pore pressure time history, frequency content, acceleration response spectrum, and amplification ratio of acceleration. This study extends the discussion of the limits of applicability of the $u$–$p$ formulation with respect to the rigorous solution of Biot's equations (obtained here with $u$–$U$ formulation) to the context of a complex dynamic regime provided by the vertical components of real earthquake records, and paves the way for further investigations.