Probabilistic macroseismic hazard assessment for Nicaragua (preliminary results)

A probabilistic macroseismic hazard assessment has been done for Nicaragua. For this, the most complete catalogue for Central America, compiled by NORSAR in Norway has been used. In this catalogue, empirical intensity attenuation relations were found. Using these empirical relations, magnitudes were changed to epicentral intensities expected in sites where no intensities had been reported. The calculated intensities from a polygon surrounding Nicaragua were used to assess the macroseismic hazard in the region. For the whole polygon, the cumulative intensity frequency was calculated resulting in a b-value of 0.60 for an intensity interval of V–IX. The time completeness was also studied indicating that, for strong events causing higher intensities (I ₀ VII), the catalogue is complete for events that have been recorded since 1840. The whole polygon was cut into independent seismotectonic regions where the statistical procedure (intensity frequency and time completeness) was done.     

A multiresolution strategy for solving landslides using the Particle Finite Element Method

We present an approach for the simulation of landslides using the Particle Finite Element Method of the second generation. In this work, the multiphase nature (granular phase and water) of the phenomenon is considered in a staggered fashion using a single, indeformable Finite Element mesh. A fractional step and a monolithic strategy are used for the water flow and granular phase, respectively. In this way, the maximum accuracy with minimal computational times is reached. The method is completed by adding the interaction terms due to drag and pressure forces, together with a moving mesh strategy to reduce the size of the computational domain.     

Die Bedeutung des elektromagnetischen Erdfeldes in der Bioklimatologie

Zusammenfassung Viele meteorobiologische Untersuchungen lassen vermuten, daß kolloidelektrische Vorgänge im Übertragungsmechanismus zwischen Umwelt und Organismen eine bedeutsame Rolle spielen. Diese Hinweise werden diskutiert und insbesondere die geoelektrischen Faktoren besprochen, die hierin von Einfluß sein können; als Indikatoren erscheinen Erdströme besonders geeignet. An speziellen Erdstromregistrierungen werden eine Anzahl atmosphärischer Einflüsse nachgewiesen. Registrierungen von elektromagnetischen Feldstörungen können aber darüber hinaus auch für die allgemeine Meteorologie und die Wettervorhersage bedeutungsvoll sein.

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Summary A great number of meteorobiological investigations induce to suppose that colloido-electric processes are of great importance for the mechanism of transmission between environment and organism. These aspects are discussed and especially the geo-electric factors which therein may have a considerable influence, whereof earth-currents are especially qualified as indicators. Different atmospheric influences are showed by special records of earth-currents; beyond it, the records of electromagnetic field perturbations seem to be important for general meteorology and for weather-forecasting.

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Résumé De nombreuses recherches météorobiologiques conduisent à l'hypothèse que des processus colloido-électriques jouent un rôle important dans le mécanisme de translation entre milieu et organisme. Ces aspects sont discutéet et surtout les facteurs géoélectriques qui peuvent y avoir une influence; comme indicateurs les courants telluriques paraissent être au premier plan. Certaines influences atmosphériques sont démontrées par des enregistrements spéciaux de courant tellurique. Par-dessus cela, des enregistrements des perturbations du champs électromagnétique peuvent être de grande importance pour la météorologie générale et pour les prévisions du temps.

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Mit 4 Textabbildungen.     

Due casi di grave inquinamento di acque sotterranee

Riassunto Ricercate le cause e le modalità secondo le quali si è verificato un vasto inquinamento da cromati alcalini nella falda acquifera della zona di Spinetta Marengo (Alessandria), l'A., mediante il rilevamento chimico-colorimetrico della diffusione dell'inquinamento, esaminate le caratteristiche della falda, introduce un nuovo metodo per determinare analiticamente e graficamente le variazioni della concentrazione. — A proposito di altro inquinamento da arseniato sodico verificatosi in un pozzo al Muggiano (La Spezia) vengono esaminate le caratteristiche in rapporto alla natura geologica del terreno.

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Summary The A. had researched the cause and modality of the large defilement of alkalines chromates in the ground-water-flow of the zone of Spinetta Marengo (Alessandria). By means of chemical and colourimetrical methods, he examined the characteristics of the diffusion of the defilement and present a new method to determine analytically and graphically the variation of the concentration in every point of the zone. — After, the A. examined an other defilement of sodium-arseniate in a well of Muggiano (La Spezia) in reference to the geological feature of the ground.

     

Monitoring of a methane-seeping pockmark by cabled benthic observatory (Patras Gulf, Greece)

A new seafloor observatory, the gas monitoring module (GMM), has been developed for continuous and long-term measurements of methane and hydrogen sulphide concentrations in seawater, integrated with temperature (T), pressure (P) and conductivity data at the seafloor. GMM was deployed in April 2004 within an active gas-bearing pockmark in the Gulf of Patras (Greece), at a water depth of 42 m. Through a submarine cable linked to an onshore station, it was possible to remotely check, via direct phone connection, GMM functioning and to receive data in near-real time. Recordings were carried out in two consecutive campaigns over the periods April–July 2004, and September 2004–January 2005, amounting to a combined dataset of ca. 6.5 months. This represents the first long-term monitoring ever done on gas leakage from pockmarks by means of CH₄+H₂S+T+P sensors. The results show frequent T and P drops associated with gas peaks, more than 60 events in 6.5 months, likely due to intermittent, pulsation-like seepage. Decreases in temperature in the order of 0.1–1°C (up to 1.7°C) below an ambient T of ca. 17°C (annual average) were associated with short-lived pulses (10–60 min) of increased CH₄+H₂S concentrations. This seepage “pulsation” can either be an active process driven by pressure build-up in the pockmark sediments, or a passive fluid release due to hydrostatic pressure drops induced by bottom currents cascading into the pockmark depression. Redundancy and comparison of data from different sensors were fundamental to interpret subtle proxy signals of temperature and pressure which would not be understood using only one sensor.     

The effect of air-bubble barriers in containing oil-slick movement

Laboratory experiments were carried out to investigate the performance of an air-bubble barrier and to determine the oil volume passage rate through such a barrier under various oil sample, wind, wave and current conditions. Two empirical equations were derived based on the laboratory data. The first equation determines the relationship between current velocity and the minimum airflow rate required to avoid oil flow through the barrier from the surface. The second equation predicts the dimensionless oil volume passage rate through the barrier under the surface per unit width when the required minimum airflow rate is given in order to prevent oil flow through the barrier from the surface. If the current and wind speed are given, both the minimum required airflow rate for avoiding oil flow through the barrier from the surface, and the dimensionless oil volume passage rate through the barrier under the surface per unit width can be determined.     

Internal tidal bore warm fronts and settlement of invertebrates in central Chile

We studied the occurrence of large high frequency temperature fluctuations and their potential association with settlement of intertidal invertebrates during the spring/summer period 1999/2000 at Las Cruces, on the coast of central Chile. Our results showed the existence of internal tidal bores, characterized by sharp drops in water temperature at the surface and near the bottom, and subsequent temperature increases, which occurred with a semidiurnal periodicity. Measured currents support the hypothesis of alternating onshore and offshore movement of warm-water fronts. The frequency of the events varied through the summer and their amplitude seems to be modulated by onshore winds. The strongest events were observed when strong onshore winds occurred in late afternoon hours and the entire water column showed a semidiurnal temperature signal. Highest values of chlorophyll concentration in the intertidal zone and daily settlement of bivalves, gastropods and crustaceans were observed at times when conditions were favorable for occurrence of internal tidal bores. Results suggest that internal tidal bore warm fronts could play an important role in the transport of neustonic larval invertebrates and the delivery of phytoplankton to at least some intertidal sites along the coast of Chile.     

Modeling the influence of hydroperiod and vegetation on the cross-sectional formation of tidal channels

The evolution of the cross section of a salt-marsh channel is explored using a numerical model. Deposition on the marsh platform and erosion and deposition in the channel affect the tidal prism flowing through the cross section, such that the model captures the evolution of the stage–discharge relationship as the channel and marsh platform evolve. The model also captures the growth of salt-marsh vegetation on the marsh platform, and how this vegetation affects flow resistance and the rate of sedimentation. The model is utilized to study the influence of hydroperiod and vegetation encroachment on channel cross section. Numerical results show that a reduction in hydroperiod due to the emergence of the marsh platform causes an infilling of the channel. Vegetation encroachment on the marsh surface produces an increase in flow resistance and accretion due to organic and mineral sedimentation, with important consequences for the shape of the channel cross section. Finally, modeling results indicate that in microtidal marshes with vegetation dominated by Spartina alterniflora, the width-to-depth ratio of the channels decreases when the tidal flats evolve in salt marshes, whereas the cross-sectional area remains proportional to the tidal peak discharge throughout channel evolution.