Optimizing interpolation of shoot density data from a Posidonia oceanica seagrass bed

A case study on the optimization of Posidonia oceanica density interpolation, using a data set from a large meadow at Porto Conte Bay (NW Sardinia, Italy), is presented. Ordinary point kriging, cokriging and a weighted average based on inverse square distance were used to interpolate density data measured in 36 sampling stations. The results obtained from different methods were then compared by means of a leave‐one‐out cross‐validation procedure. The scale at which interpolation was carried out was defined on the basis of the Hausdorff dimension of the variogram. Optimizing spatial scale and data points search strategy allowed obtaining more accurate density estimates independently of the interpolation method.     

Growth of the Mediterranean Gorgonian Lophogorgia ceratophyta (L., 1758)

Abstract. Growth of the shallow-water gorgonian Lophogorgia ceratophyta was investigated in an infralittoral station located in La Spezia Gulf, Ligurian Sea. Mean annual height growth rate was estimated to be 2.57 cm · a^-1. The fractal dimension of the colonies was found to gradually evolve in complexity, exhibiting a simpler branching pattern in younger specimens. The maintenance of a low, invariable ramification complexity as an optimal choice in managing relationships between water and the colony's living tissues is also discussed.     

Magnetic anisotropy produced by magma flow: theoretical model and experimental data from Ferrar dolerite sills (Antarctica)

Volcanic rocks forming sills, dykes or lava flows may display a magnetic anisotropy derived from the viscous flow during their emplacement. We model a sill as a steady-state flow of a Bingham fluid, driven by a pressure gradient in a horizontal conduit. The magma velocity as a function of depth is calculated from the motion and constitutive equations. Vorticity and strain rate are determined for a reference system moving with the fluid. The angular velocity and the orientation of an ellipsoidal magnetic grain immersed in the fluid are calculated as functions of time or strain. Magnetic susceptibility is then calculated for a large number of grains with a uniform distribution of initial orientations. It is shown that the magnetic lineation oscillates in the vertical plane through the magma flow direction, and that the magnetic foliation plane changes periodically from horizontal to vertical. The results are compared with the magnetic fabric of Ferrar dolerite sills (Victoria Land, East Antarctica) derived from low-field susceptibility measurements.     

Fluid flow and pore pressure development throughout the evolution of a trough mouth fan,western Barents Sea

Using a combination of geophysical and geotechnical data from Storfjorden Trough Mouth Fan off southern Svalbard, we investigate the hydrogeology of the continental margin and how this is affected by Quaternary glacial advances and retreats over the continental shelf. The geotechnical results show that plumites, deposited during the deglaciation, have high porosities, permeabilities and compressibilities with respect to glacigenic debris flows and tills. These results together with margin stratigraphic models obtained from seismic reflection data were used as input for numerical finite element models to understand focusing of interstitial fluids on glaciated continental margins. The modelled evolution of the Storfjorden TMF shows that tills formed on the shelf following the onset of glacial sedimentation (ca. 1.5 Ma) acted as aquitards and therefore played a significant role in decreasing the vertical fluid flow towards the sea floor and diverting it towards the slope. The model shows that high overpressure ratios (up to λ ca. 0.6) developed below the shelf edge and on the middle slope. A more detailed model for the last 220 kyrs accounting for ice loading during glacial maxima shows that the formation of these aquitards on the shelf focused fluid flow towards the most permeable plumite sediments on the slope. The less permeable glacigenic debris flows that were deposited during glacial maxima on the slope hinder fluid evacuation from plumites allowing high overpressure ratios (up to λ ca. 0.7) to develop in the shallowest plumite layers. These high overpressures likely persist to the Present and are a critical precondition for submarine slope failure.     

A note on climate change adaptation for seaports: a challenge for global ports, a challenge for global society

With 80 % of world trade carried by sea, seaports provide crucial linkages in global supply-chains and are essential for the ability of all countries to access global markets. Seaports are likely to be affected directly and indirectly by climatic changes, with broader implications for international trade and development. Due to their coastal location, seaports are particularly vulnerable to extreme weather events associated with increasing sea levels and tropical storm activity, as illustrated by hurricane “Sandy”. In view of their strategic role as part of the globalized trading system, adapting ports in different parts of the world to the impacts of climate change is of considerable importance. Reflecting the views of a diverse group of stakeholders with expertise in climate science, engineering, economics, policy, and port management, this essay highlights the climate change challenge for ports and suggests a way forward through the adoption of some initial measures. These include both “soft” and “hard” adaptations that may be spearheaded by individual port entities, but will require collaboration and support from a broad range of public and private sector stakeholders and from society at large. In particular, the essay highlights a need to shift to more holistic planning, investment and operation.     

The Central-Western Mediterranean: Anomalous igneous activity in an anomalous collisional tectonic setting

The central-western Mediterranean area is a key region for understanding the complex interaction between igneous activity and tectonics. In this review, the specific geochemical character of several ‘subduction-related’ Cenozoic igneous provinces are described with a view to identifying the processes responsible for the modifications of their sources. Different petrogenetic models are reviewed in the light of competing geological and geodynamic scenarios proposed in the literature.Plutonic rocks occur almost exclusively in the Eocene–Oligocene Periadriatic Province of the Alps while relatively minor plutonic bodies (mostly Miocene in age) crop out in N Morocco, S Spain and N Algeria. Igneous activity is otherwise confined to lava flows and dykes accompanied by relatively greater volumes of pyroclastic (often ignimbritic) products. Overall, the igneous activity spanned a wide temporal range, from middle Eocene (such as the Periadriatic Province) to the present (as in the Neapolitan of southern Italy). The magmatic products are mostly SiO₂-oversaturated, showing calcalkaline to high-K calcalcaline affinity, except in some areas (as in peninsular Italy) where potassic to ultrapotassic compositions prevail. The ultrapotassic magmas (which include leucitites to leucite-phonolites) are dominantly SiO₂-undersaturated, although rare, SiO₂-saturated (i.e., leucite-free lamproites) appear over much of this region, examples being in the Betics (southeast Spain), the northwest Alps, northeast Corsica (France), Tuscany (northwest Italy), southeast Tyrrhenian Sea (Cornacya Seamount) and possibly in the Tell region (northeast Algeria).Excepted for the Alpine case, subduction-related igneous activity is strictly linked to the formation of the Mediterranean Sea. This Sea, at least in its central and western sectors, is made up of several young (< 30 Ma) V-shaped back-arc basins plus several dispersed continental fragments, originally in crustal continuity with the European plate (Sardinia, Corsica, Balearic Islands, Kabylies, Calabria, Peloritani Mountains). The bulk of igneous activity in the central-western Mediterranean is believed to have tapped mantle ‘wedge’ regions, metasomatized by pressure-related dehydration of the subducting slabs. The presence of subduction-related igneous rocks with a wide range of chemical composition has been related to the interplay of several factors among which the pre-metasomatic composition of the mantle wedges (i.e., fertile vs. refractory mineralogy), the composition of the subducting plate (i.e., the type and amount of sediment cover and the alteration state of the crust), the variable thermo-baric conditions of magma formation, coupled with variable molar concentrations of CO₂ and H₂O in the fluid phase released by the subducting plates are the most important.Compared to classic collisional settings (e.g., Himalayas), the central-western Mediterranean area shows a range of unusual geological and magmatological features. These include: a) the rapid formation of extensional basins in an overall compressional setting related to Africa-Europe convergence; b) centrifugal wave of both compressive and extensional tectonics starting from a ‘pivotal’ region around the Gulf of Lyon; c) the development of concomitant Cenozoic subduction zones with different subduction and tectonic transport directions; d) subduction ‘inversion’ events (e.g., currently along the Maghrebian coast and in northern Sicily, previously at the southern paleo-European margin); e) a repeated temporal pattern whereby subduction-related magmatic activity gives way to magmas of intraplate geochemical type; f) the late-stage appearance of magmas with collision-related ‘exotic’ (potassic to ultrapotassic) compositions, generally absent from simple subduction settings; g) the relative scarcity of typical calcalkaline magmas along the Italian peninsula; h) the absence of igneous activity where it might well be expected (e.g., above the hanging-wall of the Late Cretaceous–Eocene Adria–Europe subduction system in the Alps); i) voluminous production of subduction-related magmas coeval with extensional tectonic régimes (e.g., during Oligo-Miocene Sardinian Trough formation).To summarize, these salient central-western Mediterranean features, characterizing a late-stage of the classic ‘Wilson Cycle’ offer a ‘template’ for interpreting magmatic compositions in analogous settings elsewhere.     

Addressing non-uniqueness in linearized multichannel surface wave inversion

The multichannel analysis of the surface waves method is based on the inversion of observed Rayleigh-wave phase-velocity dispersion curves to estimate the shear-wave velocity profile of the site under investigation. This inverse problem is nonlinear and it is often solved using 'local' or linearized inversion strategies. Among linearized inversion algorithms, least-squares methods are widely used in research and prevailing in commercial software; the main drawback of this class of methods is their limited capability to explore the model parameter space. The possibility for the estimated solution to be trapped in local minima of the objective function strongly depends on the degree of nonuniqueness of the problem, which can be reduced by an adequate model parameterization and/or imposing constraints on the solution.
In this article, a linearized algorithm based on inequality constraints is introduced for the inversion of observed dispersion curves; this provides a flexible way to insert a priori information as well as physical constraints into the inversion process. As linearized inversion methods are strongly dependent on the choice of the initial model and on the accuracy of partial derivative calculations, these factors are carefully reviewed. Attention is also focused on the appraisal of the inverted solution, using resolution analysis and uncertainty estimation together with a posteriori effective-velocity modelling. Efficiency and stability of the proposed approach are demonstrated using both synthetic and real data; in the latter case, cross-hole S-wave velocity measurements are blind-compared with the results of the inversion process.     

Simplified seismic performance assessment and implications for seismic design

The last decade or so has seen the development of refined performance-based earthquake engineering(PBEE) approaches that now provide a framework for estimation of a range of important decision variables,such as repair costs,repair time and number of casualties. This paper reviews current tools for PBEE,including the PACT software,and examines the possibility of extending the innovative displacement-based assessment approach as a simplified structural analysis option for performance assessment. Details of the displacement-based s+eismic assessment method are reviewed and a simple means of quickly assessing multiple hazard levels is proposed. Furthermore,proposals for a simple definition of collapse fragility and relations between equivalent single-degree-of-freedom characteristics and multi-degree-of-freedom story drift and floor acceleration demands are discussed,highlighting needs for future research. To illustrate the potential of the methodology,performance measures obtained from the simplified method are compared with those computed using the results of incremental dynamic analyses within the PEER performance-based earthquake engineering framework,applied to a benchmark building. The comparison illustrates that the simplified method could be a very effective conceptual seismic design tool. The advantages and disadvantages of the simplified approach are discussed and potential implications of advanced seismic performance assessments for conceptual seismic design are highlighted through examination of different case study scenarios including different structural configurations.