A class-oriented mechanical approach for seismic damage assessment of RC buildings subjected to the 2009 L’Aquila earthquake

The simplified mechanical method POST (PushOver on Shear Type models) for seismic vulnerability assessment of RC buildings is used in this study to derive damage scenarios for a database of 7597 RC buildings subjected to the 2009 L’Aquila earthquake. POST allows the evaluation of fragility curves through the determination of the non-linear static response of RC buildings in closed form, assuming the hypothesis of shear type behaviour, and considering the influence of infill panels both in the derivation of structural response and in assessment of building damage, which is defined according to the European Macroseismic Scale EMS-98. The aim of the present study is to provide a much more significant and reliable validation of the methodology, thanks to a much wider database compared to previous studies, and based on a different application of the methodology, i.e. at building class-level instead of single building-level. To this aim, the main geometrical-typological characteristics of the analysed buildings (number of storeys, age of construction, building area) have been statistically characterized based on data collected from post-earthquake AeDES survey forms, considering both the variability of each single parameter and the correlation that exists between one parameter and the other. This also allows to analyse the effectiveness of the adopted analytical procedure in predicting the general trends of observed damage with these parameters, showing a good agreement between observed and predicted trends. The overall predicted damage scenarios are compared with the corresponding observed ones, collected from AeDES survey forms, highlighting, again, a good agreement. Finally, the assumed mechanical interpretation of damage classification of EMS-98 is validated through the comparison between the distributions of damage to vertical structures and infill panels and the corresponding observed post-earthquake damage data.     

Delineating coastal groundwater discharge processes in a wetland area by means of electrical resistivity imaging, 224Ra and 222Rn

Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and ²²²Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (²²⁴Ra, ²²²Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.     

Noble gas systematics of the Réunion mantle plume source and the origin of primordial noble gases in Earth’s mantle

New noble gas data of ultramafic xenoliths from Réunion Island, Indian Ocean, further constrain the characteristics of primordial and radiogenic noble gases in Earth’s mantle plume reservoirs. The mantle source excess of nucleogenic ²¹Ne is significantly higher than for the Hawaiian and Icelandic plume reservoirs, similar to excess of radiogenic ⁴He. ⁴⁰Ar/³⁶Ar of the Réunion mantle source can be constrained to range between 8000 and 12 000, significant ¹²⁹Xe and fission Xe excess are present. Regarding the relative contribution of primordial and radiogenic rare gas nuclides, the Réunion mantle source is intermediate between Loihi- and MORB-type reservoirs. This confirms the compositional diversity of plume sources recognized in other radioisotope systematics. Another major result of this study is the identification of the same basic primordial component previously found for the Hawaiian and Icelandic mantle plumes and the MORB reservoir. It is a hybrid of solar-type He and Ne, and ‘atmosphere-like’ or ‘planetary’ Ar, Kr, Xe (Science 288 (2000) 1036). ²⁰Ne/²²Ne ratios extend to maximum values close to 12.5 (Ne-B), which is the typical signature of solar neon implanted as solar corpuscular radiation. This suggests that Earth’s solar-type noble gas inventory was acquired by small (less than km-sized) precursor planetesimals that were irradiated by an active early sun in the accretion disk after nebular gas dissipation, or, alternatively, that planetesimals incorporated constituents irradiated in transparent regions of the solar nebula. Previously, such an early irradiation scenario was suggested for carbonaceous chondrites which follow common volatile depletion trends in the sequence CI–CM–CV–Earth. In turn, CV chondrites closely match Earth’s mantle composition in ²⁰Ne/²²Ne, ³⁶Ar/²²Ne and ³⁶Ar/³⁸Ar. This indicates that mantle Ar could well be a planetary component inherited from precursor planetesimals. However, a corresponding conclusion for mantle Kr and Xe is less convincing yet, but this may be just due to the lack of appropriate ‘meteoritic’ building blocks matching terrestrial composition. Alternatively, heavy noble gases in Earth’s mantle could be due to admixing of severely fractionated air, but this effect must have affected all mantle sources to a very similar extent, e.g. by global subduction before the last homogenization of the mantle reservoirs.     

Diffuse Emission of Hydrogen from Poás Volcano,Costa Rica,America Central

We report the results of four soil H₂ surveys carried out in 2000–2003 at Poás volcano, Costa Rica, to investigate the soil H₂ distribution and evaluate the diffuse H₂ emission as a potential surveillance tool for Poás volcano. Soil gas H₂ contents showed a wide range of concentration from 0.2 to 7,059 ppmV during the four surveys. Maps of soil gas H₂ based on Sequential Gaussian Simulation showed low H₂ concentration values in the soil atmosphere (<0.7 ppmV) for most of the study area, whereas high soil gas H₂ values were observed inside the active crater of Poás. A significant increase in soil gas H₂ concentration was observed inside the active crater during 2001 and 2002 with respect to year 2000, followed by a decrease in 2003. The observed spatial and temporal variations of soil H₂ concentration have been well correlated with seismicity, microgravimetry and fumarolic chemistry changes which occurred during this study. These observations evidence changes in the shallow magmatic-hydrothermal system of Poás, and it might be related to a potential magmatic intrusion during the period 1998–2004. Therefore, monitoring diffuse H₂ emission of Poás has become an important geochemical tool for the monitoring of its volcanic activity.     

Landslide detection in the Himalayas using machine learning algorithms and U-Net

Landslides - Event-based landslide inventories are essential sources to broaden our understanding of the causal relationship between triggering events and the occurring landslides. Moreover,...     

Phytoplankton,protozooplankton and nutrient dynamics in the Bornholm Basin (Baltic Sea) in 2002–2003 during the German GLOBEC Project

From March 2002 to until April 2003 we investigated the seasonal nutrient and phytoplankton dynamics in the central Bornholm Basin (Baltic Sea) within the framework of the German GLOBEC Project. We choose a nested approach consisting of vertical fluorescence profiles, phytoplankton counts and nutrient analyses. The Fluoroprobe (MultiProbe, BBE Moldaenke) is capable of distinguishing four algal groups (Cryptophyceae, Cyanophyceae, Chlorophyceae, Bacillariophyceae + Dinophyceae). Winter nutrient concentrations were about 5 μM NO₃ and 0.5 μM PO₄ in the central Basin. The spring phytoplankton bloom was dominated by the diatom Skeletonema sp. and reached a maximum of about 270 μg C/l before the onset of the seasonal stratification. Protozooplankton was dominated by the Mesodinium rubrum (a phototrophic ciliate = Myrionecta rubra) and reached a maximum biomass of about 200–300 μg C/l about 2 weeks after the demise of the diatom spring bloom. During summer, the water column was stratified and a subsurface maximum developed near the thermocline consisting of Bacillariophyceae, Cryptophycea and other phototrophic flagellates. Phytoplankton and protozooplankton biomass was generally low. Nutrient concentrations point towards a nitrogen limitation during this period. The stratification period ended during September and surface nutrient concentrations increased again. Protozooplankton reached a second maximum during September. With the Fluoroprobe small scale structures in the plankton community could be detected like a subsurface Cryptophyceae maximum near the thermocline that however, could not be confirmed by cell counts. The chlorophyll a estimate of the Fluoroprobe was in good agreement with the phytoplankton biomass estimated from counts. We conclude that only by combining modern sensing technology with microscopy, the small-scale dynamics and taxonomic spectrum of the plankton can be fully captured.     

Adaptations of araphid pennate diatoms to a planktonic existence

Pennate diatoms are monophyletic. Their principal cell wall elements, called valves, are shaped like a ship's hull. Within the pennates, the araphids are paraphyletic; they possess rimoportulae and pore fields located at the valve apices. The pore fields exude mucilage pads with which cells attach to one another to form chains. Many taxa use the pads also for attachment to substrata. Only a few genera are truly planktonic. The main question addressed in this study is whether the planktonic lifestyle is ancestral or derived. Phylogenies inferred from nuclear SSU rDNA gene sequences of diatoms indicated that the attached lifestyle is ancestral among the araphids, whereas a typically planktonic lifestyle seems to have developed at least three times and possibly four times independently. Acquisition of a planktonic lifestyle from benthic ancestry was accompanied by a reduction in the silicification of cell-wall elements, but changes in morphological characters shared by all four clades were not detected. The reason why only three or four araphid pennate clades have adopted a planktonic lifestyle may be related to constraints associated to their sexual reproduction mode. Partner cells of opposite mating type align with one another and produce isogametes. These gametes lack flagella; they move to one another in an amoeboid fashion, which functions well on surfaces, but seems a liability in a turbulent water column. The planktonic lineages must have overcome this constraint, e.g. by sinking to the bottom, or aggregating, to perform sexual reproduction. Members of the four araphid pennate lineages are now common constituents of the plankton, suggesting that they are ecologically successful.     

An overview on the seismicity of Cuba

The seismicity of Cuba is briefly presented together with a few fundamental neotectonic elements of the adjacent Caribbean region. The Cuban seismicity catalogue has been extended back to 1528 and it shows that the largest earthquakes occurred in 1766 and 1852 (I = IX MSK). Two types of seismicity (intraplate and interplate) can be distinguished in Cuba. Western and Eastern Seismotectonic Units correspond to intraplate type and the Southeastern Seismotectonic Unit to interplate type. Western Cuba is characterized by a low frequency of earthquake occurrence. Distribution of epicenters is not regular and the most important events mainly concentrate along two regional active fault system (Nortecubana and Surcubana). Due to the lack of seismic stations in this region, the characterization of seismicity is frequently done on the grounds of historical data available from 1693. The main seismogenic source for Cuba is the Bartlett-Cayman fault system, but inland there are other active structures. Some issues about historical and present day Cuban seismological research are also showed.