Accounting for directionality as a function of structural typology in performance‐based earthquake engineering design

For the seismic design of a structure, horizontal ground shaking is usually considered in two perpendicular directions, even though real horizontal ground motions are complex two‐dimensional phenomena that impose different demands at different orientations. While the issue of ground motion dependence on the orientation of the recording devices has been the focus of many significant developments during the last decade, the effects of directionality on the characteristics of the structure have received less attention. This work presents a proposal to calculate the probability of exceedance of elastic spectral displacements accounting for structural typology and illustrates its relevance by means of its application to two case‐study buildings. In order to ease its implementation in seismic design codes, a simplification is developed by means of a detailed statistical analysis of the results obtained using four sets of real hazard curves. The framework presented herein is considered to represent an important contribution to the field of performance‐based earthquake engineering, permitting improved treatment of directionality effects within seismic risk design and assessment. Copyright © 2016 John Wiley & Sons, Ltd.     

The Mediterranean intercalibration exercise on soft‐bottom benthic invertebrates with special emphasis on the Italian situation

The intercalibration exercise is an important step in the building process of the surface water ecological quality assessment, which is required by the Water Framework Directive (WFD). Its aim is to apply the water quality classification in a uniform manner to all the Member States belonging to the same eco‐region. Cyprus, France, Greece, Italy, Slovenia and Spain participated in the soft‐bottom benthic invertebrate subgroup for the Mediterranean coastal region. The methodologies proposed by Member States were applied and tested; the results were compared and harmonized to establish agreed and comparable boundaries for the benthic invertebrate ecological status classes. The national methods used in the intercalibration process were: for Cyprus and Greece, the Bentix Index; for Slovenia, a combination of AZTI Marine Biotic Index (AMBI), richness and diversity with the use of factor and discriminant analysis (Multimetric AMBI); for Spain, a new index, named MEDOCC, which is an adaptation of the AMBI index to the Western Mediterranean area. Italy and France tested different methods, none of which have been officially adopted. Final class boundary values for the different official classification systems were obtained and compared. Besides describing methods and results obtained by the different countries, the Italian situation is examined in more detail. All the above methods have been applied to Italian data, but the results were not conclusive. Major causes for concern are related to insufficient sites and data, to the lack of real non‐impacted reference sites, and to the difficulties in validating the ecological status classification in sites not showing a pollution gradient.     

The spreading of eutrophication in the eastern coast of the Gulf of Bothnia,northern Baltic Sea – An analysis in time and space

In the Baltic Sea, the Gulf of Bothnia is the only sub-basin with only minor effects of eutrophication mainly due to physical factors. Most evaluations of the state of the Gulf of Bothnia are based on offshore investigations. In the present study the coastal zone of the eastern Gulf of Bothnia is analysed. Long-term data (1980–2007) of total nitrogen and phosphorus, turbidity and oxygen are analysed using principal component analysis (PCA) for spatial and temporal patterns in the trophic situation. The coastal zone is divided into six regions: inner and outer areas of the Bothnian Sea and the Quark, and the outer areas of the southern and northern Bothnian Bay. The results show a degradation of water quality from north to south, and from outer to inner coastal areas. Eutrophication changes from an almost non-existing problem in the Bothnian Bay in the north to clear signs of nutrient over-enrichment in the Bothnian Sea. This shows that even if eutrophication in the Gulf of Bothnia is not serious, the increasing trends in nutrient levels should be seen as warning signals for the future, and remedies to combat eutrophication should be taken rapidly.     

Melting and cataclastic features in shatter cones in basalt from the Vista Alegre impact structure,Brazil

Shatter cones are one of the most widely recognized pieces of evidence for meteorite impact events on Earth, but the process responsible for their formation is still debated. Evidence of melting on shatter cone surfaces has been rarely reported in the literature from terrestrial impact craters but has been recently observed in impact experiments. Although several models for shatter cones formation have been proposed, so far, no one can explain all the observed features. Shatter cones' from the Vista Alegre impact structure, Brazil, formed in fine‐grained basalt of the Jurassic‐Cretaceous Serra Geral Formation (Paraná large igneous province). A continuous quenched melt film, consisting of a crystalline phase, mica, and amorphous material, decorates the striated surface. Ultracataclasites, containing subrounded pyroxene clasts in an ultrafine‐grained matrix, occur subparallel to the striated surface. Several techniques were applied to characterize the crystalline phase in the melt, including Raman spectroscopy and transmission electron microscopy. Results are not consistent with any known mineral, but they do suggest a possible rare or new type of clinopyroxene. This peculiar evidence of melting and cataclasis in relation with shatter cone surfaces is interpreted as the result of tensile fracturing at the tip of a fast propagating shock‐induced rupture, which led to the formation of shatter cones at the tail of the shock front, likely during the early stage of the impact events.     

Paleomagnetic and rock-magnetic survey of eocene dike swarms from the Tecalitlan area (Western Mexico): Tectonic implications

For long time the western-central Mexico has been affected by oblique subduction caused by Farallon plate beneath North America. As result, smaller plates (e.g. Cocos Plate), several fault systems outlining crustal blocks (e.g. Michoacán block) and magmatic arcs (e.g. Paleocene-Early Oligocene magmatism and the Trans-Mexican Volcanic Belt) were developed. Still, no paleomagnetic data are available for Oligocene and Miocene. The principal aim of this study is to evaluate whether the tectonic rotations and relative motions of these blocks occurred before the Miocene. Here, we report a detailed rock-magnetic and paleomagnetic results from Tecalitlan area, located in the Michoacán block. Sixteen sites (about 150 oriented samples) were collected including one radiometrically dated diabase dike (35.0 ± 1.8 Ma). Rock-magnetic experiments permitted identification of magnetic carriers and assessment of the paleomagnetic stability. Continuous susceptibility measurements vs temperature in most cases yield reasonably reversible curves with Curie points close to that of magnetite. Reliable paleomagnetic directions were obtained for 12 sites. Inclination I and declination D of the mean paleomagnetic direction obtained in this study are I = 33.1°, D = 345.0°, and Fisherian statistical parameters are k = 25, α₉₅ = 8.9°. The corresponding mean paleomagnetic pole position is P_lat = 75.7°, P_long = 166.6°, K = 31, A₉₅ = 8.0°. The mean inclination is in reasonably good agreement with the expected value, as derived from reference poles for the stable North America. Magnetic declination is not significantly different from that expected which is in disagreement with a counterclockwise tectonic rotation of about 20° previously reported for the studied area. Based on paleomagnetic results obtained in this study compiled with those currently available from the Michoacán Block, we propose a simple model suggesting that sometime in Eocene epoch the convergence vector of the Farallon plate relative to North America plate was normal to the trench before reaching an actual oblique convergence.     

Shifts in an epibenthic trophic web across a marine frontal area in the Southwestern Atlantic (Argentina)

Marine benthic trophic relationships and food web structures may be influenced by benthic–pelagic coupling processes, which could also be intensified by the physical dynamics of marine fronts. In this work, we employed stable isotope (δ¹³C and δ¹⁵N) analysis to investigate the influence of the Southwest (SW) Atlantic shelf-break front (SBF; 38–39°S, 55–56°W; Argentina) on an epibenthic trophic web. Epibenthic organisms were sampled, at depths of ~ 100 m, with a non-selective dredge from a sandy bottom community located in frontal (F) and marginal (M) areas. The SBF position and the chlorophyll-a (chl-a) concentrations were inferred using satellite data of the sea surface temperature (SST) and satellite chl-a concentration, respectively. The most noticeable shifts in stable isotopes between the sampled areas were those of the Patagonian scallop, Zygochlamys patagonica (δ¹³C), and those of the sea urchin, Sterechinus agassizi (δ¹⁵N). Diet analyses inferred from stable isotopes and mixing models demonstrated that the dominant component of this community, Z. patagonica, had variable contributions to higher trophic levels between areas. More importantly, the epibenthic assemblage in F areas showed δ¹³C-enriched and δ¹⁵N-depleted isotopic signatures with respect to the M areas. Collectively, this evidence suggests that frontal dynamics promotes the accumulation of δ¹³C-enriched phytoplankton in the seabed in F areas, while in M areas the more degraded organic matter becomes more important in the trophic web, decreasing the δ¹⁵N isotopic signature of the assemblage. Therefore, the trophic web was sustained by fresher food in F areas than in M areas, demonstrating the role of frontal dynamics in the shaping of these communities.     

Assembly of Pampia to the SW Gondwana margin: A case of strike-slip docking?

Different hypotheses have been proposed to account for the geologic evolution of the southwestern margin of Gondwana in the Early Paleozoic, involving accretion and displacement of different terranes in a protracted convergent margin. In order to constrain and understand the kinematic and paleogeographic evolution of the Pampia terrane a paleomagnetic study was carried out in different Cambrian to Devonian units of the Eastern Cordillera (Cordillera Oriental) and the Interandean Zone (Interandino) of NW Argentina. Paleomagnetic poles from the Campanario Formation (Middle to Upper Cambrian): 1.5°N 1.9°E A₉₅ = 9.2° K = 37.46 N = 8; and Santa Rosita Formation (Lower Ordovician): 8.6°N 355.3°E A₉₅ = 10.1° K = 26.78 n = 9, representative of the Pampia terrane, are interpreted to indicate a Late Cambrian significant displacement with respect to the Río de la Plata and other Gondwana cratons. A model, compatible with several geological evidences that explains this displacement in the framework of the final stages of Gondwana assembly is presented. We propose a simple dextral strike-slip kinematic model in which Pampia and Antofalla (? Arequipa?) blocks moved during Late Cambrian times from a position at the present southern border of the Kalahari craton into its final position next to the Rio de la Plata craton by the Early Ordovician.     

Presence of plastic debris in loggerhead turtle stranded along the Tuscany coasts of the Pelagos Sanctuary for Mediterranean Marine Mammals (Italy)

This work evaluated the presence and the frequency of occurrence of marine litter in the gastrointestinal tract of 31 Caretta caretta found stranded or accidentally bycaught in the North Tyrrhenian Sea. Marine debris were present in 71% of specimens and were subdivided in different categories according to Fulmar Protocol (OSPAR 2008). The main type of marine debris found was user plastic, with the main occurrence of sheetlike user plastic. The small juveniles showed a mean ± SD of marine debris items of 19.00 ± 23.84, while the adult specimens showed higher values of marine litter if compared with the juveniles (26.87 ± 35.85). The occurrence of marine debris observed in this work confirms the high impact of marine debris in the Mediterranean Sea in respect to other seas and oceans, and highlights the importance of Caretta caretta as good indicator for marine litter in the Marine Strategy Framework Directive (MSFD) of European Union.     

Is net ecosystem production higher in natural relative to constructed wetlands?

Ecosystem metabolism is an important measure of wetland restoration efficiency, and serves to indicate if the system is capable of processing energetic resources. Despite its value, ecosystem metabolism has rarely been included in monitoring programs. In this study, we aimed to achieve the following objectives: (i) compare net ecosystem production (NEP) rates of constructed vs. natural wetlands; (ii) identify the highest NEP rate habitats; and (iii) define the main environmental factors regulating NEP in different wetland types. Pelagic and benthic NEP rates and physicochemical features were measured in three natural and five constructed wetlands in the middle Ebro River floodplain (NE Spain). Statistical analyses showed pelagic NEP rates peaked in natural wetlands, which produced up to 187.5 mg C m^?3 h^?1 compared to lower rates in constructed wetlands (up to 46.2 mg C m^?3 h^?1). Pelagic NEP responded positively to temperature, total dissolved solids, and nutrients. Benthic NEP rates were 3 to 30-fold greater than pelagic in natural (up to 994.9 mg C m^?3 h^?1) and constructed (up to 1,551.5 mg C m^?3 h^?1) wetlands, and were heavily influenced by habitat type, with NEP peaking in areas dominated by submerged vegetation and fine organic sediment. Rapid recovery in aquatic communities (i.e. macroinvertebrate diversity) has been previously reported for the studied wetlands; however, our study suggests a slower recovery of functional processes (i.e. pelagic NEP) in constructed habitats. We therefore strongly advocate the inclusion of ecosystem function in the design and evaluation of restoration projects to optimise long-term wetland ecosystem sustainability.