Weak Contrast PP Wave Displacement R/T Coefficients in Weakly Anisotropic Elastic Media

—Approximate PP plane wave displacement coefficients of reflection and transmission for weak contrast interfaces separating weakly but arbitrarily anisotropic elastic media are presented. The PP reflection coefficient for such an interface has been derived recently by Vavry?uk and P?en?ík (1997). The PP transmission coefficient presented in this paper was derived by the same approach. The coefficients are given as a sum of the coefficient for the weak contrast interface separating two nearby isotropic media and a term depending linearly on contrasts of the so-called weak anisotropy (WA) parameters (parameters specifying deviation of properties of the medium from isotropy), across the interface. While the reflection coefficient depends only on 8 of the complete set of the WA parameters describing P-wave phase velocity in weakly anisotropic media, the transmission coefficient depends on their complete set. The PP reflection coefficient depends on "shear-wave splitting parameter" γ. Tests of accuracy of the approximate formulae are presented on several models.     

Geoid anomalies over two South Atlantic fracture zones

Seasat altimetry profiles across the Falkland-Agulhas fracture zone (FZ) and the Ascension FZ in the South Atlantic were examined for evidence of step-like geoid offsets predicted from thermal modeling of the lithosphere. The geoid profiles exhibit much short-wavelength power and the step-like offsets are often small, making reliable estimation of the heights of the observed geoid offsets difficult. The offsets were estimated by the least-squares fitting of quadratic curves incorporating a step function to the altimetry profiles. A preferred offset value was determined for each profile by taking the average of step heights computed with various distances around the fracture zone excluded from the fit. The age of the crust surrounding the fracture zones, necessary for computing a theoretical geoid offset, was determined from surface ship magnetic anomaly data and from existing ocean floor age maps.Observed variations in geoid step height with age of the lithosphere are not consistent with those predicted from standard thermal plate models. For ages less than 30 Ma, the step offsets across both fracture zones decrease in a manner appropriate for an unusually thin plate with a thickness of 50–75 km. At greater ages, the offsets show complex behavior that may be due to bathymetric features adjacent to the fracture zones. Similar geoid patterns on opposite branches of the Falkland-Agulhas FZ are indicative of processes that act symmetrically on both sides of the Mid-Atlantic Ridge. This behavior of the geoid is consistent both with small-scale convection occurring beneath the lithosphere and with bathymetric features originally produced along the ridge crest and now located symmetrically on opposite sides of the ridge. The west flank of the Ascension FZ displays a regrowth in step height at about 40 Ma consistent with small-scale convection and in agreement with other studies of Pacific and South Atlantic fracture zones.     

Numerical modeling of reservoirs or pipes in groundwater seepage

In groundwater studies, the numerical modeling of complex boundary conditions can be made easier by considering reservoirs and pipes as “reservoir” finite elements, which can store or release large volumes of water at almost constant hydraulic head. The numerical code to be used must solve the complete conservation equation with unlinked functions for the water retention curve and the unsaturated hydraulic conductivity, and the ability to describe these as step functions. Four examples illustrate the performance of the “reservoir” element: reservoir pumping, laboratory variable-head permeability test, vertical flow in an open borehole, and pumping test with well storage.     

Performance analysis of the spaceborne laser ranging system

The Spaceborne Laser Ranging System is a proposed short pulse laser on board an orbiting spacecraft.^1,2,3,4 It measures the distance between the spacecraft and many laser retroreflectors (targets) deployed on the Earth’s surface. The precision of these range measurements is assumed to be about ±2 cm (M. W. Fitzmaurice, private communication). These measurements are then used together with the orbital dynamics of the spacecraft, to derive the relative position of the laser ground targets. Assuming a six day observing period with 50% cloud cover, uncertainties in the baseline for target separations of 50 km to 1200 km were estimated to be on the order of 1 to 3 cm and the corresponding values in the vertical direction, ranged from 1 cm to 12 cm. By redetermining the measurements of the relative target positions, the estimated precision in the baseline for a target separation of 50 km is less than 0.3 cm and for a separation of 1200 km is less than 1 cm. In the vertical direction, the estimated precision ranged from 0.4 cm to 4.0 cm respectively. As a result of the repeated estimation of the relative laser target positions, most of the non-temporal effects of error sources as exemplified by the errors in geopotential are reduced. The Spaceborne Laser Ranging System’s capability of determining baselines to a high degree of precision provides a measure of strain and strain rate as shown byCohen, 1979. These quantities are essential for crustal dynamic studies which include determination and monitoring of strain near seismic zones, land subsidence, and edifice building preceding volcanic eruptions. It is evident that such a system can also be used for geodetic surveys where such precisions are more than adquate.     

Aperçu synthétique sur la tectonique des Carpates Roumaines

Résumé À la constitution des Carpates Roumaines participent les plissements hercyniens et carpatiques.Les déformations géométriques hercyniennes ont résulté des plissements profonds déterminés par le métamorphisme régional. Elles ont influencé d'une manière de plus en plus atténuée les plissements carpatiques. Pendant le paroxisme mésocrétacé, la tectonique carpatique a engendré des nappes de décollement et des glissements grâce à un simple mécanisme, expliqué par la pesanteur.Les nappes à vergences anticarpatiques se sont formées pendant la phase laramienne. Elles sont également le résultat de la pesanteur associée à l'action de la sous-poussée.Les nappes polygénétiques sont les nappes les plus jeunes et caractérisent les zones du Flysch des Carpates Orientales.Pendant le Tertiaire, une tectonique cassante a prédominé dans les Carpates.

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The Romanian Carpathians consist of three subdivisions, each of them having its tectonical features, namely: Eastern Carpathians, Southern Carpathians and Apuseni Mountains.Their architecture consists of Hercynian and Carpathian foldings. The Hercynian tectonics is due to the deep foldings during the metamorphism which called forth the metanappes. The Hercynian foldings have printed their characters into the Carpathian tectonics and into the evolution of the palaeomesozoical sedimentary zones.During the mesocretaceous phase, the gravitational tectonics develop into the Carpathian realm, generating the gravitational nappes of the Metalliferous Mountains, the Raru-Hsma massif and the Perani Mountains.The overthrusts took place at the surface and are not due to the lateral contraction of the rocks in the depth.The anticarpathian vergences are characteristic for the Laramian nappes.The Flysch tectonics is characterized by polygenetic nappes, formed during a long period and developed all along the chain.The ruptural tectonics developed in the Romanian Carpathians during Tertiary.

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Zusammenfassung Die rumänischen Karpaten lassen sich in drei Einheiten teilen, jede mit ihrer Besonderheit: Ostkarpaten, Südkarpaten und Apuseni-Gebirge. Ihr Bau besteht aus herzynischen und karpatischen Elementen. Die herzynische Tektonik ist die Folge der während der Metamorphose entstandenen Tieffaltungen, welche Metadecken hervorgebracht haben. Die herzynischen Faltungen zeigen sich im karpatischen Bau und in der Ablagerungsgeschichte. Während der mittelkretazischen Faltungsbewegungen hat die Abscherungs- und Fließtektonik das karpatische Gebiet ergriffen und das Entstehen der Schweredecken im Erzgebirge, in den Raru- und Hsma-Massiven sowie im Perani-Gebirge bedingt. Die Decken sind die Folge der in der Nähe der Erdoberfläche ablaufenden Bewegungen und keineswegs des seitlichen Druckes der Tiefgesteine. Die laramischen Decken sind durch antikarpatische Vergenzen charakterisiert und auf die Unterschiebungen der alten Blöcke zurückzuführen. Die Tektonik des Flysches zeichnet sich durch polygenetische Decken aus, die sich während mehrerer Perioden, entlang dem Faltenstreichen, entwickelt haben. Die Bruchtektonik setzte in den rumänischen Karpaten erst während des Neozoikums ein.

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Influence of Temporal Variations in River Discharge, pH, Alkalinity and Ca on the Speciation and Concentration of Heavy Metals in Some Mining Polluted Rivers

Dissolved (dialysis in situ) and total concentrations ofCu, Zn, Cd and Al in eight mining polluted rivers in the Røros area, central Norway, were determinedby atomic absorption spectrometry (flame and graphite furnace) and compared to pH, Caconcentration and alkalinity through seasonal variations in river discharge. Totalconcentrations of the metals were highest during early spring flood and during summer andautumn rain episodes. Dissolved concentrations also increased as the spring floodproceeded, but small discharge peaks within this 2 month period as well as a considerableautumn flood episode appeared to lower rather than to raise the dissolved metal concentrations.Consequently the dissolved fractions of Zn, Cd and Al showed a significant negative correlationwith river discharge, and were low at the discharge peaks. Possibly high sediment concentrationsoccurring at high flood conditions more than counteracted desorption induced by pHdecrease, and led to decreased dissolved fractions through adsorption. Cu speciationon the other hand seemed to be more closely linked to pH. Alkalinity and Ca concentration,both assumed to protect aquatic life from metal pollution, were significantly lowerduring episodes with high Cu and Al total concentrations.     

Real Time Analysis and Forecasting of Strata Caving Behaviour during Longwall Operations

Summary. Discontinuous manual observations and irregular caving characteristics of roof rocks often lead to improper decisions resulting in accidents and production loss. Hence, systematic monitoring of the hanging roof behind the chock shields is necessary for safe and productive mining operations. A real-time application was successfully implemented in an Indian mine for forecasting of hanging roof behaviour to enhance safety and productivity. This paper reports the functioning of real-time TWAP (time weighted average pressure) analysis in the forecasting of hanging roof behaviour in real time.     

An integrated approach to investigate saline water intrusion and to identify the salinity sources in the Central Godavari delta, Andhra Pradesh, India

The Central Godavari delta is located along the Bay of Bengal Coast, Andhra Pradesh, India, and is drained by Pikaleru, Kunavaram and Vasalatippa drains. There is no groundwater pumping for agriculture as wells as for domestic purpose due to the brackish nature of the groundwater at shallow depths. The groundwater table depths vary from 0.8 to 3.4 m and in the Ravva Onshore wells, 4.5 to 13.3 m. Electrical Resistivity Tomography (ERT) surveys were carried out at several locations in the delta to delineate the aquifer geometry and to identify saline water aquifer zones. Groundwater samples collected and analyzed for major ions for assessing the saline water intrusion and to identify the salinity origin in the delta region. The results derived from ERT indicated low resistivity values in the area, which can be attributed to the existence of thick marine clays from ground surface to 12–15 m below ground level near the coast and high resistivity values are due to the presence of coarse sand with freshwater away from the coast. The resistivity values similar to saline water <0.01 Ω m is attributed to the mixing of the saline water along surface water drains. In the Ravva Onshore Terminal low resistivity values indicated up coning of saline water and mixing of saline water from Pikaleru drain. The SO ₄ ^?2 /Cl^?and Na⁺²/Cl^?ratios did not indicate saline water intrusion and the salinity is due to marine palaeosalinity, dilution of marine clays and dissolution of evaporites.     

Large-scale vertical hydroacoustic structure of the North Atlantic and its seasonal variability

A classification based on the number and types of large-scale acoustic waveguides is proposed for the mean seasonal profiles of sound speed propagation. A scheme for North Atlantic zoning, using typical curves of the sound speed vertical distribution, is given. The channel axis's position is shown not to depend on the water mass haline properties, being controlled by the temperature field vertical stratification.Translated by Vladimir A. Puchkin.