Source depletion and extent of melting in the Tongan sub-arc mantle

The fluid immobile High Field Strength Elements (HFSE) Nb and Ta can be used to distinguish between the effects of variable extents of melting and prior source depletion of the Tongan sub-arc mantle. Melting of spinel lherzolite beneath the Lau Basin back-arc spreading centres has the ability to fractionate Nb from Ta due to the greater compatibility of the latter in clinopyroxene. The identified spatial variation in plate velocities and separation of melt extraction zones, combined with extremely depleted lavas make Tonga an ideal setting in which to test models for arc melt generation and the role of back-arc magmatism.We present new data acquired by laser ablation-ICPMS of fused sample glasses produced without the use of a melt fluxing agent. The results show an arc trend towards strongly sub-chondritic Nb/Ta (< 17) with values as low as 7.2. Melting models show that large degree melts of depleted MORB mantle fail to reproduce the observed Nb/Ta. Alternatively, incorporation of residual back-arc mantle that has undergone less than 1% melting into the sub-arc melting regime reproduces arc values. However, the extent of partial melting required to produce the composition of the Lau Basin back-arc basalts averages 7%. This apparent discrepancy can be explained if only the lowermost 4 km of the residua from the mantle melt column beneath the back-arc is added to the source of arc magmas. We have identified that the degree of arc/back-arc coupling displayed in the rock record provides an index of the depth of hydrous melting beneath the arc. In this case, this would imply a depth of ~ 75 km for generation of arc magmas, indicating that hydrous melting in the mantle wedge is triggered by the breakdown of hydrous phases in the subducting slab.     

The prospects for modernizing very broadband seismometers

This paper considers the possibilities for modernizing the KSESh broadband seismic station developed earlier at the IPE AS USSR. The goal of the modernization was to extend the frequency and dynamic ranges and to decrease nonlinear distortions. The ways and concrete methods for improving the mechanical construction and electronic components of the station are shown and the intermediate results are described. As preliminary estimates show, there is an opportunity to build devices with the velocimeter response up to 520–540 s periods on the basis of this pendulum.     

Possible contribution of leakage currents from the Atlantic Ocean to the magnetic-field variations observed in Devon

It is suggested that leakage currents flow across Devon, north of Exeter, from large-scale electric-current systems induced in the Atlantic Ocean by the geomagnetic variations incident on the Atlantic Ocean from the ionosphere. This model can account for the variation with period of the contribution of induced current flow to the differences in the magnetic H variations of period > 30 s observed at Exeter and Sidmouth.     

Displacement Phenomenon of Slow and Fast Growing Species in Microorganisms Association

In the process of the biological treatment of sewage, the multicomponent system of the substrate is converted by an association of microorganisms. The composition of species of microorganisms in the system depends on the substrate available and on the conversion of substrate. For this, a mathematical model is presented, which describes the change of the composition of species according to the rate of growth of the individual species on the basis of load (substrate available/biomass). The diversity of the biological system increases with decreasing load. The model is tested by practical examples.     

A statistical study of pressure changes in the troposphere and lower stratosphere after strong solar flares

Summary The average change in height of several constant pressure levels in the troposphere and lower stratosphere after a strong solar flare is described. The analysis covers the northern hemisphere north of 10°N and is based on a sample of 81 carefully selected flares from the period July 1957 through December 1959.The statistical significance of the results is tested by drawing a comparison with the results obtained when one applies exactly the same analysis to three samples of 81 random key-dates selected from the same period.Properties of the reaction pattern are (1) it is pronounced at high as well as low latitudes, (2) it consists of alternating cells of positive and negative height change, (3) it is established within six hours after the flare, and (4) the maximum response occurs near the tropopause.It appears more likely that the atmospheric reaction pattern can be attributed to very energetic solar particles rather than to enhanced ultraviolet radiation.     

Sobre el caracter general de la clasificacion de las bahias geomagneticas y su ley de aparicion durante el dia

Summary A comparative study of the geomagnetic bays at the Observatories of Cuajimalpa and Teoloyucan (Mexico) and Tortosa, shows: 1) that the grouping of the bays into a certain number of fundamental types, and that the tendency of their frequency maxima to recur in a cyclical order during the day, are general features of geomagnetic bays, at least for all middle geomagnetic latitudes; 2) that the relative importance of the different types and the hour of their maxima varies according to the geomagnetic latitude of the Observatory where the bays are recorded.

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Résumé En comparant les baies géomagnétiques enregistrées aux Observatoires de Cuajimalpa et Teoloyucan (Mexique) avec celles observées à Tortosa, on examine la validité générale de la classification des baies établie à l'Observatoire de l'Ebre et de la loi de succession des différents types le long du jour. L'on arrive aux conclusions suivantes: 1^o La classification des baies géomagnétiques en un certain nombre de types fondamentaux, de même que la tendence à l'apparition de leurs maxima de fréquence dans un ordre cyclique pendant la journée, a un caractère général, tout au moins pour les latitudes géomagnétiques moyennes; 2^o L'importance relative des différents types et l'heure d'apparition de leurs maxima varie d'un Observatoire à l'autre, d'après leur latitude géomagnétique.

     

The Application of Petroleum Hydrocarbon Fingerprint Characterization in Site Investigation and Remediation

Tremendous resources have been and continue to be spent investigating and remediating petroleum hydrocarbon compounds (PHCs) in soil and ground water. Investigating and planning a remedial strategy for sites affected by PHCs is often a challenging task because of the complex chemical nature of the PHCs. the complex regulatory environment related to PHC cleanup, and the use of analytical methods that provide quantitation but not identification of PHCs. From a technical standpoint, the PHC impacting soil and/or ground water is frequently inadequately characterised, both in identification as well as in is general properties (solubility, toxicity). From a regulatory standpoint, promulgated or recommended total petroleum hydrocarbon (TPH) cleanup levels generally relate to assumed properties of specific unweathered products and are inconsistent among different agencies and regions. This produces a prime situation for unwillingly spending more resources on investigation or remediation than may be necessary, especially when the PHC in the subsurface has different properties from unweathered products such as gasoline or diesel.
Accurately identifying the PHC and its nature, a process known as fingerprint characterization, is critical to the determination of appropriate regulatory goals and design of cost-effective remedial approaches. This paper presents several case studies in which fingerprint characterization made a significant difference in the project outcome. In each instance the nature of the organic material was better understood, the regulatory cleanup levels were negotiated based on the nature of the material, and a remedial approach was implemented that differed significantly from and was generally less costly than what would have been required without fingerprint characterization data.     

Spatial and seasonal distribution of bacterial physiological groups in two reservoirs with different trophic levels

The spatial and seasonal distribution of the viable heterotrophic population and three heterotrophic physiological groups, i.e. ammonifyers, nitrate reducers and sulphate reducers, were studied in two reservoirs in the province of Vizcaya (Spain). Using indicative parameters, both reservoirs were classified as warm monomictics, one hypereutrophic and the other mesotrophic. A direct relation between the size of the bacterial populations and the trophic levels of the reservoirs was observed. Likewise, the distributions of the bacterial populations in the water column are basically different. In the hypereutrophic lake there is a direct relationship between the bacterial distribution and the physical-chemical environment of the reservoir that cannot be observed in the mesotrophic lake.     

Observations of vertical ground accelerations exceeding gravity during the 1997 Umbria-Marche (central Italy) earthquakes

We found extensive evidence that the vertical ground accelerations produced during the largest shock (M = 6.0) of the 1997 Umbria-Marche earthquake sequence exceeded 1g in two areas close to the heavily-damaged villages of Annifo and Colle Croce. This evidence comes from the striking observation of thousands of freshly fractured and broken rocks and stones in these areas. Some of the broken stones lie isolated on soft detritic soil while others had been previously piled up, probably a long time agoto clear the fields for farming. The freshness of the cuts and fractures and the consistency of the observations for thousands of rocks and stones in these areas indicate that these rocks were thrown upwards during the earthquake, with breakage occurring at the time of impact. Ground motion calculations consistent with the static deformation inferred from GPS and interferometry data, show that the broken stones and rocks are found in the zone where the strongest shaking took place during the earthquake and that most of the shaking there was vertical.