Tectonic structure and post-Hercynian evolution of the Serre, Calabrian Arc, southern Italy: Geological, petrological and radiometric evidences

Conflicting opinions exist concerning the structure and the post-Hercynian evolution of the Serre. The present paper deals with these topics on the basis of new geological, petrological and radiometric evidence. The composition of the so-called Stilo and Polia-Copanello units has been redefined. The above domains—former sections of upper and lower Palaeozoic continental crust respectively—came into contact, due to transcurrent movements 130–140 Ma ago. A significant vertical component during the transcurrent movements, probably, exhumed the former section of lower crust. The above domains, juxtaposed, were successively involved as a single kinematic body in the Alpine orogenesis. The results enable us to make inferences for the Calabrian Arc evolution and call attention to similarities between an Austro-Alpine element (Stilo + Polia-Copanello) of the Calabrian chain and a South-Alpine sector of the Alps (Ivrea + Ceneri zones).     

Parallel inexact constraint preconditioning for ill-conditioned consolidation problems

Constraint preconditioners have proved very efficient for the solution of ill-conditioned finite element (FE) coupled consolidation problems in a sequential computing environment. Their implementation on parallel computers, however, is not straightforward because of their inherent sequentiality. The present paper describes a novel parallel inexact constraint preconditioner (ParICP) for the efficient solution of linear algebraic systems arising from the FE discretization of the coupled poro-elasticity equations. The ParICP implementation is based on the use of the block factorized sparse approximate inverse incomplete Cholesky preconditioner, which is a very recent and effective development for the parallel preconditioning of symmetric positive definite matrices. The ParICP performance is experimented with in real 3D coupled consolidation problems, proving a scalable and efficient implementation of the constraint preconditioning for high-performance computing. ParICP appears to be a very robust algorithm for solving ill-conditioned large-size coupled models in a parallel computing environment.     

Ensemble smoothing of land subsidence measurements for reservoir geomechanical characterization

Geomechanical models are often used to predict the impact on land surface of fluid withdrawal from deep reservoirs, as well as investigating measures for mitigation. The ability to accurately simulate surface displacements, however, is often impaired by limited information on the geomechanical parameters characterizing the geological formations of interest. In this study, we employ an ensemble smoother, a data assimilation algorithm, to provide improved estimates of reservoir parameters through assimilation of measurements of both horizontal and vertical surface displacement into geomechanical model results. The method leverages the demonstrated potential of remote sensing techniques developed in the last decade to provide accurate displacement data for large areas of the land surface. For evaluation purposes, the methodology is applied to the case of a disk‐shaped reservoir embedded in a homogeneous, isotropic, and linearly elastic half space, subject to a uniform change in fluid pressure. Multiple sources of uncertainty are investigated, including the radius, R, the thickness, h, and the depth, c, of the reservoir; the pore pressure change, Δp; porous medium's vertical uniaxial compressibility, c_M, and Poisson's ratio, ν, and the ratio, s, between the compressibilities of the medium during loading and unloading cycles. Results from all simulations show that the ensemble smoother has the capability to effectively reduce the uncertainty associated with those parameters to which the variability and the spatial distribution of land surface displacements are most sensitive, namely, R, c, c_M, and s. These analyses demonstrate that the estimation of these parameters values depends on the number of measurements assimilated and the error assigned to the measurement values. Copyright © 2014 John Wiley & Sons, Ltd.     

Mathematical identification of diffuse and localized instabilities in fluid‐saturated sands

The mathematical properties of diffuse and localized failure modes in fluid‐saturated sands are investigated. The granular medium is modeled as an elastoplastic solid, and a recently proposed set of scalar indices, here referred to as moduli of instability, is used to identify the onset of potential bifurcations of the incremental response. First, the analytical properties of these moduli are discussed, stressing their dependence on the kinematic constraints associated with the imposed deformation modes. Then, by using an elastoplastic model for sands, drained and undrained loading paths are simulated under axisymmetric, plane‐strain and simple shear conditions. For each deformation mode, the instability moduli are computed and monitored throughout the simulations, with the purpose of elucidating the consequences of changes in control conditions. In addition, it is illustrated that suitable linear transformations allow the same strategy to be used to perform drained or undrained shear band analyses and predict the interval of possible band inclinations. The final comparison against literature experiments on loose Hostun sand shows that the instability moduli are indicators of the loss of resistance against specific modes of deformation. As a result, they can be used to identify and explain a number of failure mechanisms that can be commonly observed in experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Potential loading damage to industrial storage tanks due to volcanic ash fallout

The phenomenon of volcanic fallout ash from Mt. Etna in Sicily (Italy) is well known and frequent in recent years, as in the period 2001–2004. As a consequence, significant problems for the population, road, rail and air traffic and production activities have occurred. The industrial areas of Catania and Augusta-Priolo, located in south eastern Sicily, might be involved during particular weather conditions. This paper aims at determining the potential scenarios of damage to industrial facilities caused by volcanic ash fallout. The work has been focused on the study of both fixed and floating roof storage tanks, containing flammable liquids, and examines extreme failures damage causing the greatest loss of containment for these facilities. To include scenarios arising from natural phenomena (Na-Tech events) in the standard risk assessment procedure, the estimation of the vulnerability of these facilities is necessary. The study has been applied to the area surrounding Mt. Etna, and the procedure can also be extended to other case studies.     

Measuring the north–south coseismic displacement component with high‐resolution multi‐aperture InSAR

Earthquake source inversions based on space‐borne Synthetic Aperture Radar interferometry (InSAR) are used extensively. Typically, however, only the line‐of‐sight (LoS) surface displacement component is measured, which is mainly sensitive to the vertical and E–W deformations, although well‐established methods also exist to estimate the flight‐path component, which is highly sensitive to the N–S displacement. With high‐resolution sensors, these techniques are particularly appealing, because accuracies in the order of 3 cm can be achieved, while retaining spatial resolutions between 45 m and a few km, depending on the required level of filtering. We discuss the application to COSMO‐SkyMed SAR imagery of the Spectral Diversity or Multi Aperture Interferometry technique, presenting the first SAR flight‐path displacement field associated with the Mw 6.3, 2009 L'Aquila event (central Apennines). Finally, we observe and characterize a previously unknown misregistration pattern.