Applying rock mass classifications to carbonate rocks for engineering purposes with a new approach using the rock engineering system

Classical rock mass classification systems are not applicable to carbonate rocks,especially when these are affected by karst processes.Their applications to such settings could therefore result in outcomes not representative of the real stress-strain behavior.In this study,we propose a new classification of carbonate rock masses for engineering purposes,by adapting the rock engineering system(RES) method by Hudson for fractured and karstified rock masses,in order to highlight the problems of implementation of geomechanical models to carbonate rocks.This new approach allows a less rigid classification for carbonate rock masses,taking into account the local properties of the outcrops,the site conditions and the type of engineering work as well.

Analysis of the Low-Energy Seismic Activity in the Southern Apulia (Italy)

In this paper we analysed the historical and instrumental seismicity of the seismic district “Penisola Salentina” (Salento peninsula) in the southern part of the Apuliaregion, making use of the most recent seismological database. Relocation of available dataset points out that the events are spatially distributed over a belt of deformation that approximately corresponds to Soglia Messapica (Taranto-Brindisi depression). Besides, computed source characteristics indicate dextral strike-slip solutions with an approximately E-W orientation that seismologically confirm previous geodynamic studies indicating a NE-SW extension in the Taranto-Brindisi depression. In particular, the tensional stress associated to the present seismic activity could be the consequence of the relaxation of the buckling process following the extensional re-arrangement of the Apenninic belt masses. Moreover attenuation QPvalues obtained in this study are much greater than those inferred in other parts of Italian peninsula;this result agrees with previous macroseismic investigations and indicates a greater efficiency of the studied area in the transmission of body waves.

Restrictions to the application of 'diagnostic'criteria for recognizing ancient seismites

Soft-sediment deformation structures induced by seismic liquefaction and/or fluidization receive much attention in sedimentological,structural and palaeoseismic studies.The direct record of larger earthquakes is restricted to instrumental and historical data; the recognition of prehistoric earthquakes requires criteria to recognize seismites in the geological record.The areal distribution of seismites can sometimes be related to active faults since distances to the epicenter(for a given magnitude) tend to be related to the liquefaction effects of seismic shocks.The use of soft-sediment deformation structures for palaeoseismic studies has limitations,however.Hardly anything is known,for instance,about the effects that modern seismic events have on the sediments in most environments.Moreover,criteria for the recognition of seismites are still under discussion.The following characteristics seem,particularly in combination,the most reliable:(1) Soft-sediment deformation structures should occur in laterally continuous,preferably recurring horizons,separated by undeformed beds;(2) These deformation structures should be comparable with structures known to have been triggered by modern seismic activity;(3) The sedimentary basin should have experienced tectonic activity at the time when the deformations were formed; and(4) The intensity or abundance of the soft-sediment deformation structures in a presumed seismite should change laterally,depending on the distance to the epicenter.It turns out that all of these four criteria have important exceptions.(1) Soft-sediment deformation structures occurring over large lateral distances in a specific layer can be triggered also by other processes.Moreover,in environments with a low sedimentation rate,the time between successive earthquakes is often too short to allow accumulation of beds that remain undisturbed.Furthermore,total liquefaction of a sandy bed may result in the absence of deformation features.(2) No truly diagnostic soft-sediment deformation structures exist to prove seismic activity.Moreover,the final configuration of a soft-sediment deformation structure is independent of the type of trigger.(3) Seismites occur frequently in areas where seismic activity is low today.(4) The lateral changes in the intensity of soft-sediment deformation structures in seismites as a factor presumed to depend on the distances to the epicenter,pose a complicated problem.The 2012 Emilia earthquakes,for instance,affected sandy fluvial channels but not the fine-grained floodplains.It must thus be deduced that specific soft-sediment deformation structures cannot be used without additional evidence to identify seismites.In particular,the magnitude of seismic shocks and the recurrence time of main events(the most important features that allow recognition of seismites) seem to be sedimentological in nature:facies changes in space and time seem theparameters that most strongly control the occurrence,morphology,lateral extent and the vertical repetition of seismites.

The sedimentary dynamics of Sabellaria alveolata bioconstructions (Ostia,Tyrrhenian Sea, central Italy)

Sabellaria alveolata(Linnaeus 1767)is a polychaete able to build bioconstructions of different thickness,size and patchiness,in intertidal and subtidal environments.Its biological features have been the object of numerous studies worldwide.The worm reefs are formed by millions of tubes built by sand and shells(whole or in fragments)bonded together with a strong glue produced by the worm itself.Hence,Sabellaria alveolata represents a sedimentological asset for the coastal protection,since it contributes to create natural barriers against storm waves and erosion,and supplies the beach with new sandy deposits.This work shows a multidisciplinary approach to studying a bioconstruction of Sabellaria alveolata along the Latium coast(Ostia,Tyrrhenian Sea,central Italy),proposing image analysis as a novel technique to investigate worm reefs,along with classical sedimentological/ecological tools.The Sabellaria bioconstructions have been analysed at different scales of observation,suggesting the more appropriate strategies to develop a reliable model illustrating the different growth steps of these bioconstructions.

Sediment provenance of a carbonate bioclastic pocket beach—Le Dune(Ionian Sea,South Italy)

This study focuses on the analysis of a carbonate bioclastic pocket beach located along a coastal sector of the Apulia Ionian Sea,Le Dune beach,South Italy.The beach develops for about 800 m and it is exposed to the south-westerly and southerly seas.Coastal sediments range from very coarse to medium-fine sands and they are mainly composed of bioclasts(more than 90%)which include molluscs,foraminifers,echinoderms,algae branched,bryozoans,spicules of sponges and arthropods.The study area is one part of a marine protected reserve characterised by 15 different habitats of the typical Mediterranean submerged populations and the presence of Posidonia oceanica meadows.The aim of our research is to highlight the correlation between physical and biological processes influencing Le Dune beach dynamics and its sediment provenance by analysing the textural and compositional characteristics of beach sands,which is fundamental for pocket beach conservation.The beach sand analysis,deriving from textural,compositional and bioclast investigations,underlines that one of the main indicators of the beach dynamics is the bioclast component,which provides relevant information about sand provenance and sediment transport.The beach constitutes a semi-close system only nourished by the shells of organisms and by the erosion of headlands and dunes without important sediment interchange with adjacent littoral sectors.

A Second Order Finite-Difference Ghost-Point Method for Elasticity Problems on Unbounded Domains with Applications to Volcanology

We propose a finite-difference ghost-point approach for the numerical solution of Cauchy-Navier equations in linear elasticity problems on arbitrary unbounded domains.The technique is based on a smooth coordinate transformation,which maps an unbounded domain into a unit square.Arbitrary geometries are defined by suitable level-set functions.The equations are discretized by classical nine-point stencil on interior points,while boundary conditions and high order reconstructions are used to define the field variables at ghost-points,which are grid nodes external to the domain with a neighbor inside the domain.The linear system arising from such discretization is solved by a multigrid strategy.The approach is then applied to solve elasticity problems in volcanology for computing the displacement caused by pressure sources.The method is suitable to treat problems in which the geometry of the source often changes(explore the effects of different scenarios,or solve inverse problems in which the geometry itself is part of the unknown),since it does not require complex re-meshing when the geometry is modified.Several numerical tests are successfully performed,which asses the effectiveness of the present approach.