Acoustic emission during swelling and contraction tests

An expansive clayey rock belonging to the Asturias Carboniferous of NW Spain has been petrophysically characterized before, during and after swelling tests. The evolution of the microfissuring and the induced deterioration have been studied by acoustic emission during tests and by ultrasonic techniques before and after swelling/contraction cycles. A good correlation has been found between the AE curves and swelling strain. Damage due to the generation and growth of microfissures is most important during the first moments of each swelling/contraction cycle. Microfissures mainly develop in the direction of the foliation planes, as can be shown by linear crack density and measurements of the propagation velocity of longitudinal waves.     

Le complexe filonien de Fuerteventura (Iles Canaries)

Two sectors in the island have been distinguished which depend on the intensity of the penetration of the dyke swarm: the central-western sector, where the proportion of dykes in relation to the host rocks is — in some cases — more than 90% and all the rest of the island, where the dykes are in less proportion. In the central-western sector the predominant direction varies from N-10^o-E to N-20^o-E, whilst in the rest of the island a clear constant direction does not exist, although there are some directional trends more or less well defined. Most dykes are of basaltic composition, but there are also salic dykes (trachytic and phonolitic) and camptonites. The dykes from the western sector have suffered intense transformation processes (albitization and amphibolization), so that it is frequent to find dykes that do not preserve practically any one of their primary minerals. As the albitization process also affects the host rocks and has a regional development; we can speak of a regional metamorphism equivalent in its intensity to the Green Schist. Three main generations of dykes have been established: 1st) those of an approximately N-S direction, forming the older generation, constituted by multiple injections, 2nd) those genetically related to the Basaltic Series I, 3rd) those of salic composition, closely related with the syenitic-trachytic intrusions.     

Measurement of copper release rates from antifouling paint under laboratory and in situ conditions: implications for loading estimation to marine water bodies

The release of biocides, such as copper (Cu), from antifouling (AF) coatings on vessel hulls represents a significant proportion of overall Cu loading in those harbors and estuaries where substantial numbers of small craft or large vessels are berthed. Copper release rates were measured on several self-polishing, tin-free coatings and an ablative Cu reference coating applied to steel panels using three measurement methods. The panels were exposed in natural seawater in San Diego Bay, and release rates were measured both in the laboratory and field over 2 years. Results with the static (20 cm x 30 cm) panels indicated that Cu release rates were initially high (25-65 microg Cu cm(-2)day(-1)), with a large range of values between paint types. Release rates declined to substantially lower rates (8-22 microg cm(-2)day(-1)) with reduced variability within 2 months. Release rates continued to decrease over time for approximately 6 months when relatively constant release rates were observed for most coatings. Over time, relative differences in Cu release rates measured by three exposure methods decreased, with all coatings exhibiting similar behavior toward the end of the study. Lowest overall Cu release rates were observed with the self-polishing experimental paint no. 7 in static-dynamic and in situ treatments. The highest periodic release rates were measured from panels that experienced periods of both static and dynamic exposure (8.7 ms(-1) rotation). The lowest release rates were measured from panels that experienced static, constant depth exposure, and where release rates were evaluated in situ, using a novel diver-deployed measurement system. Results from this in situ technique suggests that it more closely reflects actual Cu release rates on vessel hulls measured with intact natural biofilms under ambient conditions than measurements using standardized laboratory release rate methods. In situ measurements made directly on the AF surface of vessels demonstrated typically lower release rates than from the panel studies, averaging 8.2 microg cm(-2)day(-1) on pleasure craft, and 3.8 microg cm(-2)day(-1) on Navy vessels. The data suggest that the presence of an established biofilm likely serves to moderate the release of Cu from field-exposed antifouling coatings both on panels and hull surfaces.     

Loss on ignition: a qualitative or quantitative method for organic matter and carbonate mineral content in sediments?

Since the publication of the paper of , loss on ignition (LOI) has been widely used as a method to estimate the amount of organic matter and carbonate mineral content (and indirectly of organic and inorganic carbon) in sediments. The relationships between LOI at 550 °C (LOI₅₅₀) and organic carbon (OC) content and between LOI at 950 °C (LOI₉₅₀) and inorganic carbon (IC) content are currently accepted as a standard. However, the comparison of 150 analyses of samples of diverse lithologies, collected from a single core, reveals that these relationships are affected by sediment composition (presence of clays, salts, and the variable content of organic carbon). This results in an incremental error on the estimation of carbon content from LOI values that invalidates the use of LOI values as a quantitative method for estimating carbon content. Conversely, the general trends of LOI₅₅₀ and LOI₉₅₀ show a good correlation with carbon content (both organic and inorganic) allowing use of LOI as a qualitative test for carbon content. Similarly, in our case, LOI at 105 °C (LOI₁₀₅) is a good qualitative proxy for the trends in gypsum content.     

Cu isotopic fractionation in the supergene environment with and without bacteria

The isotopic composition of dissolved Cu and solid Cu-rich minerals [δ⁶⁵Cu (‰) = (⁶⁵Cu/⁶³Cu_sample/⁶⁵Cu/⁶³Cu_std) - 1)*1000] were monitored in batch oxidative dissolution experiments with and without Thiobacillus ferrooxidans. Aqueous copper in leach fluids released during abiotic oxidation of both chalcocite and chalcopyrite was isotopically heavier (δ⁶⁵Cu = 5.34‰ and δ⁶⁵Cu = 1.90‰, respectively, [±0.16 at 2σ]) than the initial starting material (δ⁶⁵Cu = 2.60 ± 0.16‰ and δ⁶⁵Cu = 0.58 ± 0.16‰, respectively). Isotopic mass balance between the starting material, aqueous copper, and secondary minerals precipitated in these experiments explains the heavier isotopic values of aqueous copper. In contrast, aqueous copper from leached chalcocite and chalcopyrite inoculated with Thiobacillus ferrooxidans was isotopically similar to the starting material. The lack of fractionation of the aqueous copper in the biotic experiments can best be explained by assuming a sink for isotopically heavy copper present in the bacteria cells with δ⁶⁵Cu = 5.59 ± 0.16‰. Consistent with this inference, amorphous Cu-Fe oxide minerals are observed surrounding cell membranes of Thiobacillus grown in the presence of dissolved Cu and Fe.Extrapolating these experiments to natural supergene environments implies that release of isotopically heavy aqueous Cu from oxidative leach caps, especially under abiotic conditions, should result in precipitates in underlying enrichment blankets that are isotopically heavy. Where iron-oxidizing cells are involved, isotopically heavy oxidized Cu entrained in cellular material may become associated with leach caps, causing the released aqueous Cu to be less isotopically enriched in the heavy isotope than predicted for the abiotic system. Rayleigh fractionation trends with fractionation factors calculated from our experiments for both biotic and abiotic conditions are consistent with large numbers of individual abiotic or biotic leaching events, explaining the supergene chalcocites in the Morenci and Silver Bell porphyry copper deposits.     

Visualization of Volcanic Rock Geochemical Data and Classification with Artificial Neural Networks

An unsupervised neural network technique, Growing Cell Structures (GCS) was used to visualize geochemical differences between four different island arc volcanic rock types: basalts, andesites, dacites and rhyolites. The output of the method shows the cluster structure of the dataset clearly, and the relevant geochemical patterns and relationships between its variables. The data can be separated into four clusters, each associated with a specific volcanic rock type (basalt, andesite, dacite and rhyolite), according to a unique combination of major element concentrations. Following clustering, performance of the trained GCS network as a classifier of volcanic rock type was tested using two test datasets with major element concentration data for 312 and 496 island arc volcanic rock samples of known volcanic type. Preliminary classification results are promising. In the first test dataset 94% of basalts, 76% of andesites, 83% of dacites and 100% of the rhyolites were classified correctly. Successful classification rates in the second dataset were 100%, 80%, 77%, and 98% respectively. The success of the analysis suggests that neural networks analysis constitutes a useful analytical tool for identification of natural clusters and examination of the relationships between numeric variables in large datasets, and that can be used for automatic classification of new data.     

Seismic activity at the western Pyrenean edge

The present-day seismicity at the westernmost part of the Pyrenean domain reported from permanent networks is of low to moderate magnitude. However, it is poorly constrained due to the scarce station coverage of the area. We present new seismic data collected from a temporary network deployed there for 17 months that provides an enhanced image of the seismic activity and its tectonic implications. Our results delineate the westward continuity of the E–W Pyrenean band of seismicity, through the Variscan Basque Massifs along the Leiza Fault, ending up at the Hendaya Fault. This seismicity belt is distributed on a crustal scale, dipping northward to almost 30 km depth. Other relevant seismic events located in the area can be related to the central segment of the Pamplona fault, and to different E–W thrust structures.     

Evaluation of residual drift demands in regular multi‐storey frames for performance‐based seismic assessment

This paper summarizes results of a comprehensive analytical study aimed at evaluating the amplitude and heightwise distribution of residual drift demands in multi‐storey moment‐resisting frames after earthquake excitation. For that purpose, a family of 12 one‐bay two‐dimensional generic frame models was subjected to an ensemble of 40 ground motions scaled to different intensities. In this investigation, an inelastic ground motion intensity measure was employed to scale each record, which allowed reducing the record‐to‐record variability in the estimation of residual drift demands. The results were statistically processed in order to evaluate the influence of ground motion intensity, number of stories, period of vibration, frame mechanism, system overstrength, and hysteretic behaviour on central tendency of residual drift demands. In addition, a special emphasis was given to evaluate the uncertainty in the estimation of residual drift demands. Results of incremental dynamic analyses indicate that the amplitude and heightwise distribution of residual drift demands strongly depends on the frame mechanism, the heightwise system structural overstrength and the component hysteretic behaviour. An important conclusion for performance‐based assessment is that the evaluation of residual drift demands involves significantly larger levels of uncertainty (i.e. record‐to‐record variability) than that of maximum drift demands, which suggests that this variability and corresponding uncertainty should be explicitly taken into account when estimating residual drift demands during performance‐based seismic assessment of frame buildings. Copyright © 2006 John Wiley & Sons, Ltd.     

Ground Water Replenishment with Reclaimed Water in the City of Los Angeles

A two-year pilot study involving the recharge of a ground water basin with reclaimed water was completed in the city of Los Angeles. The city's Department of Water and Power is planning to initiate several ground water recharge projects using reclaimed water in the near future. One such project is the Headworks Recharge Project, the focus of this paper, Approximately 1 cfs of the Los Angeles (LA) River water comprised of 70% tertiary treated reclaimed water was recharged on a two-day wet and five-day dry cycle. The recharge water was then extracted from the basin approximately 1000 feet downgradient. Results showed greater than 4-log removal of coliform bacteria, up to 87% reduction in TOC, and compliance of the product water with federal and state drinking water standards. Model simulation showed after 15 years of recharging 3000 acre-feet per year of the LA River water and extracting about 10,000 acre-feet from the basin, the product water would contain from 5% to 15% reclaimed water. This is well below the maximum allowable limit of 20% stipulated by the California regulation.     

Nd-Sr isotope composition of lower crustal xenoliths — Evidence for the origin of mid-tertiary felsic volcanics in Mexico

Isotopic data were collected on lower crustal xenoliths to constrain the Mexican lower crust as source material for the mid-Tertiary Sierra Madre Occidental, which is one of the largest silicic volcanic piles known. The xenoliths are predominantly pelitic gneisses and mafic orthogneisses that were brought to the surface on the eastern edge of the Sierra Madre Occidental by recent alkalic basalts. The pelitic gneisses are uniform in mineral assemblage and contain garnet+quartz+plagioclase+sanidine+rutile +sillimanite/kyanite+graphite. The orthogneisses are plagioclase, garnet and/or spinel bearing two pyroxene granulites. Available geothermometric and geobarometric data show that the xenoliths equilibrated at temperatures and pressures consistent with those of the mantle/crust boundary in those areas.The xenoliths range from 46.2 to 67.2 SiO₂. Paragneisses are in general more silicic than the orthogneisses. The xenoliths have Rb concentrations between 0.4 and 97 ppm but most samples are very low, with less than 3 ppm Rb. The Sr isotopic ratios of orthogneisses from the lowermost crust throughout most of northern Mexico are very similar and range from ca. 0.705 to 0.706. Previous studies indicate that these rocks have measured (inNd) values between+2 and –5. Paragneiss xenoliths are generally more radiogenic in Sr isotopic ratio, up to 0.730, and have lower _Nd values of–11.The Nd and Sr isotopic characteristics of the orthogneisses are similar to those of the voluminous mid-Tertiary ignimbrites of the Sierra Madre Occidental. The xenoliths cannot represent cumulate material produced during the mid-Tertiary volcanism because they are Paleozoic or older. Consequently, based on Sr and Nd isotopic data, the silicic ignimbrites could comprise up to 100% lower crustal material.