Experimental analysis of the seismic response of one base-isolation building according to different levels of shaking: example of the Martinique earthquake (2007/11/29) Mw 7.3

In recent years, many studies have been focused on the use and effectiveness of passive islotaing devices for reducing the effect of seismic ground motion on buildings. Among the available methods, one consists in isolating the structure using rubber bearings, the solution certainly the most accomplished and having the most feedback. In this study, we focused on the case of Martinique earthquake (Mw=7.4) of 29 November 2007, recorded by accelerometric stations installed at the Centre de Découverte des Sciences de la Terre (Martinique), a base-isolation building with rubber bearings. Several earthquakes are used in this paper, from moderate to strong ground motion. Ambient vibration modal analysis is first described in order to understand the elastic response of the building. The earthquake data are then interpreted, in particular to understand the mechanism of vibration of the structure and its comparison with the experimental modes previously estimated using ambient vibrations.     

Determination of the 3D structure of an earthflow by geophysical methods: The case of Super Sauze, in the French southern Alps

In order to evaluate the risk associated by an earthflow to abruptly evolve into a torrential flow, the knowledge of its internal structure is necessary. Geotechnical methods are important to reach this goal. However, because of the rough topography associated with earthflows, their surface heterogeneities, and the spatial variations of the thickness of the potentially moving mass, non-intrusive geophysical methods offer a very useful tool that complements traditional geotechnical methods. We report the results of a comprehensive study covering a 150 m by 200 m area of the Super Sauze earthflow. This earthflow developed in black marls in the southern French Alps. Shallow electrical conductivity investigations, derived using low frequency domain electromagnetics, maps hidden gullies and crests and lateral variations of the clay and the water content within the first 5 m below the ground surface. Electrical resistivity tomography allows to extrapolate this information down to 10 m below the ground surface along selected transects. The vertical structure of the earthflow, down to the substratum, is defined precisely thanks to joint inversion of DC and TDEM vertical soundings along one profile: the flowing upper layer and the position of the substratum are clearly evidenced. Combining this geophysical datasets with geotechnical tests and drill holes, we provide an estimate of both the location and the volume of the potentially most dangerous areas of the earthflow.     

Responses of benthic macrofauna and biogeochemical fluxes to various levels of mussel biodeposition: An in situ “benthocosm” experiment

An in situ experiment was done to evaluate the dose-dependent response of mussel biodeposition on benthic communities and biogeochemical fluxes. Natural benthic communities were exposed to 7 different levels of mussel biodeposition (equivalent to that produced by 0-764 mussels m⁻²) over 50 days. Benthic communities responded as predicted from the Pearson, T.H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanogr. Mar. Biol. Annu. Rev. 16, 229-311 model of organic enrichment. Total abundance and species richness decreased with increasing biodeposition. The abundance and biomass of opportunistic species (Capitella spp.) increased in the mesocosms subject to the greatest biodeposition. Sensitive species Tellina agilis and Pherusa plumosa tended to decrease in abundance and biomass with increasing biodeposition. The biotic index M-AMBI responded clearly to increased biodeposition and may be a useful tool for assessing the effect of mussel biodeposition on the benthic environment. These results are important for the construction of predictive models for determining environmental carrying capacity for bivalve aquaculture.     

Influence of an oxygen minimum zone and macroalgal enrichment on benthic megafaunal community composition in a NE Pacific submarine canyon

Megafaunal diversity in the deep sea shows a parabolic pattern with depth. It can be affected by factors such as low oxygen concentration, which suppresses diversity, or the presence of submarine canyons, which enhances it. Barkley Canyon, located off the west coast of British Columbia, Canada, is a submarine canyon that extends from the continental margin (200 m) into the deep ocean (2,000 m). This canyon receives drift kelp from shoreline kelp forests and contains an oxygen minimum zone (OMZ) at 500 to 1,500 m depth. Our study investigated the abundance and diversity of epibenthic megafauna over a range of depths (200–2,000 m) and oxygen concentrations (0.5–5.0 ml/L) within Barkley Canyon, as well as changes in abundance near detrital kelp. Video was collected using the remotely operated vehicle ROPOS along seven 1‐km cross‐canyon (i.e., across the axis of the canyon) transects and three 40‐m perpendicular cross‐transects over kelp. Taxonomic groups were associated with depth, temperature, and the presence of pebbles. The OMZ restricted pennatulids, and edge effects along OMZ boundaries were observed for ophiuroids. The geomorphology of the sea floor affected the distribution of taxa across the canyon, with Porifera mainly found along the walls and Echinoidea within the canyon axis. Expected richness exhibited a bimodal pattern, peaking at 300 and 2,000 m, possibly due to the combined effect of the OMZ and the submarine canyon. Echinoidea aggregated near drift kelp at 200 and 300 m. We found that faunal communities in Barkley Canyon were influenced by several confounded factors including depth, oxygen and substrate. Understanding faunal patterns is paramount with increased exploitation and a changing climate.     

Electrical spectroscopy of porous rocks: a review—II. Experimental results and interpretation

In the frequency range from millihertz to hundreds of megahertz, many different physical and physico-chemical processes contribute to the electrical polarization of porous water-bearing rocks. This makes the interpretation of their electrical spectra a complicated problem and requires both elaborate theories and model experiments. At high frequencies, the Maxwell–Wagner–Bruggeman–Hanai (MWBH) theory of effective media, which takes into account only bulk properties, shape and partial volume of components, is very appropriate. At low frequencies, surface films, polarization of the electrical double layer (EDL) and clustering of conductive components can produce very strong polarization; corresponding theoretical models are considered in a companion paper ( Chelidze & Gueguen 1999 , hereafter referred to as Paper I). This paper is devoted to the review of experimental data and their comparison with theoretical models.
  Experiments on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water-bearing rocks and the dominance of this contribution over MWBH values at low frequencies. The effective dielectric constant of porous saturated rocks increases with the surface-to-volume ratio of the system and strongly depends on the surface charge ( ζ potential). At ζ potential, equal to zero, the low-frequency dielectric permittivity (DP) is minimal. The experimental data on relaxation times and the magnitude of the surface polarization of water-bearing porous systems can be satisfactorily explained by theories of film polarization, diffusional polarization generated by deformation of an 'open' electrical double layer (EDL) and percolation.     

The macrozoobenthos of the Karavasta lagoon system (Albania): local assemblages and geographical comparisons

The macrozoobenthic assemblage from the Karavasta lagoon system, the main wetland of Albania, was studied on soft bottoms and artificial hard substrates. Three different communities were identified: the typical ‘brackish‐water community’, an ‘outlet community’ dominated by filter‐feeders, and a typical ‘marine community’, inhabiting fine sandy bottoms, where polychaetes are dominant, together with a few species of tunicates and bivalves, which colonize hard substrates. The occurrence of build‐ups of the bryozoan Conopeum seurati, settled on the upper portion of long submerged wooden poles, was the main feature of faunistic interest. The faunistic affinity between the zoobenthic assemblage recorded in the hyperhaline lagoon of Karavasta and the assemblages from two Italian lagoons, the brackish Lake of Lesina and the euhaline Lake of Fogliano, was considered according to the different hydrological conditions and the geographical location. Hydrological confinement and salinity were likely to be the leading factors influencing the benthic community composition in the Karavasta wetland area. Therefore, on a vaster spatial scale, the isolation and geographical proximity of the ecosystems and colonizing ability and dispersal changes of the species appear to be the main factors liable to produce faunal variations.     

The influence of extraction rate on the reduced sulphur content of Aix-les-Bains’ thermal spring waters: Consequences for resource-quality monitoring

Sulphurous thermal springs account for a few percent of all thermal springs. As each degree of oxidation of elemental S corresponds to a different S species, sulphurous spring waters may contain a variety of S species. Total S content is one of the parameters measured when analysis is carried out for issuing a spa’s operating licence. Under French law these parameters must be stable over time. The two spas in Aix-les-Bains are fed by a number of natural springs and boreholes, whose waters have total reduced S concentrations of between 30 and 800 mg L⁻¹. To ensure compliance with the requirements of the spas’ operating licences, particularly in terms of total reduced S content, official analysis of the waters is carried out every month at random dates and times. Monthly analyses have revealed seasonal variations in the S content of some of Aix-les-Bains’ springs; therefore, more frequent monitoring was carried out in order to investigate the extent and causes of these fluctuations. As well as seasonal variations, this monitoring has revealed daily and hourly fluctuations that appear to be related to extraction rates. For some of the springs and boreholes, S concentrations were correlated with extraction rates; for others, an increase in extraction rate led to a reduction in total S content. Concentrations of sulphide ions (one of the species included in the total sulphur analyses) were monitored at the same time as the total S content. Variations in sulphide ion concentrations and in sulphide concentration/total S ratios did not appear to be linked to variations in flow rate. These tests show that random monthly testing is not suitable for monitoring the stability of S contents, as this parameter can only be considered stable in terms of its yearly mean value.     

Is flooding in Toronto a concern?

Toronto is the largest city in Canada with a population of about 5.5 million in the Greater Toronto Area (GTA). Being located at the shores of Lake Ontario of the Great Lakes, which is the largest surface freshwater system in the world, and affected by air masses originating from the Gulf of Mexico, the Atlantic Ocean, and the Arctic, the city is vulnerable to extreme weather phenomena in socioeconomic and geographical terms. This short paper gives a brief overview of the history of main flooding occurrences in Toronto with an emphasis on the recent flooding of July 2013. An analysis of causes and physical dynamics of the event is presented using the structure of the watersheds and weather systems in the region. Based on the flood risk vulnerability assessment carried out on the 2013 flooding, several weaknesses in critical infrastructure and critical facilities have been highlighted. Future considerations and recommendations include revisiting of the flood damage mitigation strategies (e.g., use of new and adaptive infrastructure designs, social media, crowd-sourcing information), flood zoning update, tax incentives, insurance options, and retrofitting solutions for those living in flood-prone areas.