Forced oscillation measurements of seismic wave attenuation and stiffness moduli dispersion in glycerine-saturated Berea sandstone

Fluid pressure diffusion occurring on the microscopic scale is believed to be a significant source of intrinsic attenuation of mechanical waves propagating through fully saturated porous rocks. The so-called squirt flow arises from compressibility heterogeneities in the microstructure of the rocks. To study squirt flow experimentally at seismic frequencies the forced oscillation method is the most adequate, but such studies are still scarce. Here we present the results of forced hydrostatic and axial oscillation experiments on dry and glycerine-saturated Berea sandstone, from which we determine the dynamic stiffness moduli and attenuation at micro-seismic and seismic frequencies (0.004–30 Hz). We observe frequency-dependent attenuation and the associated moduli dispersion in response to the drained–undrained transition (∼0.1 Hz) and squirt flow (>3 Hz), which are in fairly good agreement with the results of the corresponding analytical solutions. The comparison with very similar experiments performed also on Berea sandstone in addition shows that squirt flow can potentially be a source of wave attenuation across a wide range of frequencies because of its sensitivity to small variations in the rock microstructure, especially in the aspect ratio of micro-cracks or grain contacts.     

Sparse Bayesian linearized amplitude-versus-angle inversion

The technique of seismic amplitude-versus-angle inversion has been widely used to estimate lithology and fluid properties in seismic exploration. The amplitude-versus-angle inversion problem is intrinsically ill-posed and generally stabilized by the use of L2-norm regularization methods but with drawback of smoothing important boundaries between adjacent layers. In this study, we propose a sparse Bayesian linearized solution for amplitude-versus-angle inversion problem to preserve the sharp geological interfaces. In this regard, a priori constraint term with two regularization functions is presented: the sparse constraint regularization and the low-frequency model information. In addition, to obtain high-resolution reflectivity estimation, the model parameters decorrelation technique combined with dipole decomposition method is employed. We validate the applicability of the presented method by both synthetic and real seismic data from the Gulf of Mexico. The accuracy improvement of the presented method is also confirmed by comparing the results with the commonly used Bayesian linearized amplitude-versus-angle inversion.     

Chemical defenses against generalist fish predators and fouling organisms in two invasive ahermatypic corals in the genus Tubastraea

The introduction of exotic marine species has caused considerable economic and ecological damage around the world. Some of these species possess adaptations such as secondary metabolites which facilitate their successful invasion into new areas. In this study we tested two hypotheses: (i) crude extracts produced by two invasive hard corals Tubastraea coccinea and Tubastraea tagusensis, introduced to the southwest Atlantic, inhibit predation by generalist fish; (ii) substances found in the crude extracts of both species reduce or enhance the settlement of other organisms. In an in situ palatability bioassay the extract of T. tagusensis reduced predation by generalist fish. The extracts of both species of coral showed species‐specific effects on fouling organisms in in situ gel plate bioassays. Control and extract plates had similar total cover, although plates with extracts had significantly fewer Cladophora sp., and Lithophyllum sp. was only detected on control gels. In contrast, a hydrozoan was only found on plates with extracts and overall community ordination demonstrated clear differences in the fouling communities between treatments. These results demonstrate that both coral species have chemical substances which can bring about a negative interaction with potential fish predators and competitors such as algal and invertebrate foulers and the advantage gained could explain their success in invading new regions to the detriment of local fauna and flora.     

Assessing rheological properties of fluid mud samples through tuning fork data

Ocean Dynamics - At the nautical bottom approach, part of the fluid mud layers can be included in the available depth if they present favorable rheology. As it is difficult to perform in situ...     

Impacts of Holocene and modern sea-level changes on estuarine mangroves from northeastern Brazil

Projections of the impacts of modern Relative Sea Level (RSL) rise on estuarine mangroves should be supported by coastal topographic data and records of mangrove dynamics under past RSL change. This work identified inland and seaward mangrove migrations along the Jucuruçu River (Bahia, Northeastern Brazil), during the Holocene based on sedimentary features, palynological and geochemical (δ¹³C, δ¹⁵N, C/N) data integrated with digital elevation models. During the Middle Holocene, in response to RSL rise, the estuary saw mangrove forest establish up to ~37 km inland. RSL stood between -1.4 (+0.36/-2.2 m) and +1 (2.19/0.2 m) around 7400 cal yr BP, and rose to a highest position of +3.25 (4.22/2.45 m) reached around 5350 cal yr BP. That marine incursion caused the inland replacement of freshwater vegetation by mangroves on tidal flats. Since then, the estuary experienced RSL fall, reducing inland tidal water salinity towards the Late Holocene, making that the mangroves were replaced by freshwater floodplain vegetation. Today, in the seaward part of the estuary near its mouth, mangroves occupy an area of ~10 km² along tidal channels. Considering a RSL rise of 98 cm up to the end of the 21^st century, at a rate significantly higher than that of Middle Holocene RSL rise (1.5 mm/yr) and fall (0.6 mm/yr), the current mangrove substrates are expected to drown and/or eroded near the coast, while new mangroves may establish inland, at topographically higher tidal flats in nowadays freshwater-tidal zones. Mangrove area could expand over 13 km² of coastal and flood plain. Following the same interaction between RSL/climate changes and Holocene mangrove dynamics, such upstream mangrove migration may be attenuated or intensified by changes in fluvial discharge. © 2019 John Wiley & Sons, Ltd.     

Homogeneous Catalytic Ozonation of Lipids Involving Fe2+ and Mn2+: An Experimental and Modeling Study

Given the issue of lipids in effluent treatment systems and their negative impact on the environment, this study aimed to examine lipid degradation by homogenous catalytic ozonation with the aid of iron and manganese ions. This technology presents the possibility of completely mineralizing pollutants using hydroxyl radicals. Milk is chosen as the lipid source because of the high concentration of triglycerides in its matrix, this kind of lipid being the one found most frequently in food and, consequently, in effluent treatment systems. The milk pH value is controlled, and acidic, neutral, and basic conditions are evaluated. The rates of pseudo‐first‐order reactions and the effective value are estimated. It is shown that under acidic conditions low catalyst dosages are enough to cause the complete degradation of lipids. Under neutral conditions, a similar behavior is observed. Under basic conditions, higher catalyst dosages give higher reaction rates. The order of effectiveness of the catalysts under acidic and basic conditions is Fe²⁺ > Mn²⁺, with Mn²⁺ > Fe²⁺ under neutral conditions. Homogeneous catalytic ozonation is therefore efficient at lipid degradation. This technique is viable economically, since the lipid removal occurred at low ozone levels. In addition, the ions used as catalysts are naturally abundant.     

Burial metamorphic episodes in the Andean geosyncline,Central Chile

The burial metamorphism of the Andean geosynclinal deposits of Central Chile is studied. The stratigraphic units under consideration, Lower Jurassic to Upper Cretaceous and/or Lower Tertiary in age, have an accumulated thickness of 15,000 to 28,000 m, cover an area of nearly 2,500 km², and consist predominantly of basic and acid lavas, ignimbrites and volcanic-clastic sediments, deposited in marine and continental environments. Unconformities break up the sequence into several stratigraphic-structural units.A specific burial metamorphic pattern, or series, characterizes each of the units. Each series consists of a succession of mineral assemblages, the metamorphic grade increasing downwards. The isograds are essentially parallel to the bedding planes. The grade range in each series covers different intervals between the zeolite and greenschist facies. Each unconformity corresponds to a mineralogie break in the alteration, higher grade assemblages generally overlying lower grade assemblages. The downward increase in metamorphic grade as well as the mineralogie breaks seem to be unrelated to the volcanic versus sedimentary character and to the continental versus marine depositional environment of the rocks.The repeated pattern of burial metamorphism between unconformities suggests a history consisting of several burial metamorphic episodes, each taking place prior to a folding period and leaving unaffected the underlying units, which were apparently sealed up by the previous episode. This mechanism provides an explaination for the presence of such low-grade burial metamorphic facies at the bottom of a stratigraphic column as thick as that of the Andean Geosyncline.

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Zusammenfassung Die Auswirkungen der Versenkungsmetamorphose auf die Ablagerungen der andinen Geosynklinale in Mittel-Chile wurden untersucht. Die betrachteten stratigraphischen Einheiten, unterer Jura bis obere Kreide und/oder unteres Tertiär, haben eine kumulative Mächtigkeit von 15 000 bis 28 000 m; sie bedecken ein Gebiet von fast 2500 km² und bestehen in der Hauptsache aus basischen und sauren Laven, Ignimbriten und vulkanoklastischen Sedimenten, die unter marinen und kontinentalen Bedingungen abgelagert wurden. Diskordanzen unterteilen die Abfolge in mehrere stratigraphisch-strukturelle Einheiten.Jede Einheit ist in einer besonderen, für die Versenkungsmetamorphose typischen Abfolge von Mineralgesellschaften geprägt. Der Grad der Metamorphose steigt mit zunehmender Tiefe. Die Isograden verlaufen im wesentlichen parallel zu den Schichtflächen. Die Bandbreite jeder der metamorphen Mineralgesellschaften bedeckt verschiedene Intervalle zwischen der Zeolith- und Grünschiefer-Fazies. Jeder Diskordanz entspricht auch ein Sprung in der mineralogischen Zusammensetzung, wobei die höhergradigen Mineralgesellschaften in der Regel die tiefergradigen überlagern. Der mit der Tiefe zunehmende Grad der Metamorphose und die Sprünge in der mineralogischen Zusammensetzung scheinen von dem vulkanischen bzw. sedimentären Charakter der Gesteine ebenso unabhängig zu sein wie von deren marinen bzw. kontinentalen Bildungsbedingungen.Die sich wiederholenden Muster der Versenkungsmetamorphose zwischen den Diskordanzen lassen vermuten, daß mehrere Metamorphosen stattfanden, wobei jede einzelne Umwandlung vor einer Faltungsperiode ablief und die unterlagernden Einheiten unverändert ließ, die anscheinend durch die vorangegangene Metamorphose versiegelt wurden. Dieser Mechanismus liefert eine Erklärung für die niedriggradigen Fazies der Versenkungsmetamorphose im Liegenden einer so mächtigen stratigraphischen Abfolge wie der der andinen Geosynklinale.

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Resumen En este trabajo se describe el metamorfismo de sepultamiento en los depósitos del Geosinclinal Andino. Las unidades estratigráficas estudiadas son de edad jurásica inferior a cretácica superior y/o terciaria inferior, tienen un espesor acumulado de 15.000 a 28.000 m, cubren un area de aproximadamente 2.500 km² y consisten predominantemente de lavas básicas y ácidas, ignimbritas y rocas sedimentario-volcánicas, depositadas en ambiente marino y continental.Cada una de las unidades estratigráficas está caracterizada por una serie metamórfica de sepultamiento específica. Cada serie consiste de una sucesión de asociaciones minerales con un grado de metamorfismo que aumenta hacia abajo. Las isogradas son esencialmente paralelas a los planos de estratificación. El rango de grado metamórfico de cada serie abarca diferentes intervalos entre las facies de zeolita y esquistos verdes. Cada discordancia corresponde a una discontinuidad mineralógica en la alteración en la que generalmente las asociaciones de mayor grado metamórfico cubren asociaciones de menor grado. El aumento de grado hacia abajo, lo mismo que las discontinuidades mineralógicas, parecen ser independientes tanto del carácter sedimentario o volcánico como del ambiente continental o marino de la depositación.La repetición de series metamórficas de sepultamiento entre discordancias, indica varios episodios metamórficos, cada uno de ellos anterior al plegamiento de la unidad afectada; al mismo tiempo, cada episodio metamórfico dejó sin afectar las unidades subyacentes, las que aparentemente habrían sido selladas por el episodio anterior.Este mecanismo explicaría la presencia de una facies metamórfica tan baja como la que existe en el fondo de una columna estratigráfica tan potente como la del Geosinclinal Andino.

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Rain-fall modeling: An Application of Bayesian forecasting

The rainfall-runoff modeling is very useful for forecasting purposes. A good methodology for forecasting the future stream flow is a key requirement for designers and operators of water resources systems. A compromise between conceptual and classical time series modeling is applied to model the relationship between rainfall and runoff. The dynamic nonlinear model is composed of a probability distribution describing the observation, a link function relating its mean to the so called state parameters and a system of equations defining the evolution of these parameters. Its Bayesian nature permits to take into account subjective information, making forward intervention, defining monitoring schemes and introducing smoothing facilities. An application using the data of Fartura river's basin is reported. The assessment of the prior distribution is discussed and the predictive performance of the linear and the non-linear models is reported.     

Neural network modelling of wave overtopping at coastal structures

A method has been developed to estimate wave overtopping discharges for a wide range of coastal structures. The prediction method is based on Neural Network modelling. For this purpose use is made of a data set obtained from a large number of physical model tests (collected within the framework of the European project CLASH, see e.g. [Steendam, G.J., Van der Meer, J.W., Verhaeghe, H., Besley, P., Franco, L. and Van Gent, M.R.A. (2004). The international database on wave overtopping. World Scientific, Proc. 29th ICCE, vol. 4, pp. 4301–4313, Lisbon, Portugal.]). Moreover, a method was developed to obtain confidence intervals for the overtopping predictions of the neural network.