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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 1 (1972), S. 3-3 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 1 (1972), S. 85-98 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The signal to noise ratio in tidal data in the diurnal and semidiurnal frequency bands is ordinarily so large that the noise contribution to the tidal harmonic constants is unimportant. However, as the observational locations are selected progressively closer to an amphidrome (point of no tide), the signal to noise ratio decreases, making the tidal harmonic constants less dependable. Standard deviations in amplitude of M2 and S2 obtained from 12 29-day analyses of a year of tide data obtained at a standard tide station, estimated to be 280 and 550 km away from the amphidromes for these constituents in the eastern Caribbean, are roughly one-third of the mean amplitudes for these constituents; the standard deviations in epoch are 38° and 30° respectively. Therefore, a program to locate an amphidrome precisely is self-defeating and the location can only be approximated by a grid of tide observations spanning the geographic position and/or by longer series of observations, using higher resolution to increase the signal to noise ratio. Amplitudes of 0.64 cm and 1.24 cm were calculated for M2 and S2 from a one-month series of pelagic observations obtained very close to an inferred position of the M2 amphidrome in the northeast Caribbean Sea.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 1 (1973), S. 123-145 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In this paper, we review the current state of knowledge about the acceleration of the Earth's spin, and about the closely related acceleration of the Moon. It is now established at a high confidence level that the acceleration of the Moon, when taken respect to Universal time, has changed by a large amount, and that it has even changed sign, within historic times. This almost certainly means that the acceleration of the Earth's spin has also changed by a large amount. At present we do not have enough information to say whether the changes have been in the contributions from tidal friction, in the contributions that do not arise from tidal friction, or both. Further, we do not know yet whether or not the variations in the Earth's rotation can account for the observed fluctuations in the longitudes of the Sun, the Moon, and the planets.
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  • 4
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    Electronic Resource
    Springer
    Surveys in geophysics 1 (1972), S. 27-60 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Zusammenfassung Der Rheingraben ist der mittlere Abschnitt eines'Grabengürtels, welcher Westeuropa von der Nordsee bis zum Mittelmeer durchzieht. Frühtertiäre, nephelinitische Eruptionen kündigten das Grabengeschehen an; die ersten Senkungen vollzogen sich im Mitteleozän. Der Senkungsschwerpunkt hat sich allmählich vom südlichen zum nördlichen Grabenede verlagert. Die maximale Füllmächtigkeit mit 3350 m wurde im nördlichen Abschnitt beobachtet. Die Mehrzahl der inneren und äußeren Grabenverwerfungen sind Abschiebungen. Macht man die Grabentektonik konstruktiv rückgängig, ergibt sich ein Zerrungsbetrag von 4,8 km senkrecht zur Grabenachse. Die Aufstemmung der Grabenschultern als nach außen gekippte Pultschollen hat gleichzeitig mit der Grabensenkung eingesetzt. Grabensenkung und Schulterhebung dauern bis in die Gegenwart an. Jährliche, vertikale Bewegungsraten bis zu 0,7 mm wie auch seismische Aktivität bestätigen dies. Graben und Schultern werden von einem kissenförmigen Körper mit P-Geschwindigkeiten zwischen 7,6–7,7 km s−1 unterlagert, der sich zwischen Kruste und Mantel einschiebt. Er scheint aus aufgestiegener Mantelmaterie zu bestehen. Der Graben fogt der Kammlinie dieses subkrustalen Körpers, dessen Scheitel 24 km Tiefe erreicht. Krustale Zerreißung, Grabensenkung und Schulterhebung werden auf die Bildung und das Wachstum dieses lakkolithischen Körpers zurückgeführt. Zerrungstektonik und seitliches Ausweichen der rahmenden Krustenblöcke werden einer Schweregleitung der aufgebogenen Krustenplatten zugeschrieben, wobei Aufschmelzungsvorgänge für eine mechanische Entkuppelung an der Krustenbasis sorgten. Der seitliche Versatz der Grabenachsen beim Übergang zu den Anschlußsegmenten vollzieht sich längs seismisch aktiver Querzonen mit neogenem Vulkanismus. Das Strukturgitter dieser Querzonen läßt sich auf subkrustale transform faults zurückführen. Die Tektogenese des Rheingrabens betraf in Wechselwirking die gleichen Krustenplatten wie die benachbarte alpine Orogenese. Ferner wird der Zusammenhang mit dem World Rift System diskutiert. Die erkennbaren Symptome bezüglich des Antriebsmechanismus werden ausgewertet, und sein neues Modell der Rift-Tektonik wird konzipiert.
    Notes: Abstract The Rhinegraben is the central segment of a rift system which traverses Western Europe from the North Sea to the Mediterranean. Rifting, which had started in the Middle Eocene, was preceded by early-Teriary nephelinitic eruptions. The center of maximum subsidence shifted along the graben axis from south to north during geologic times. The maximum thickness of sedimentary fill is observed in the northern part of the Rhinegraben to be as much as 3350 m. Most of the internal and external faults are normal faults. By theoretically returning the dip-slip movements and tilted block tectonics back to their original positions a lateral gap can be calculated in the amount of 4.8 km. The graben shoulders began to rise along the marginal fault scarps as outward tilted blocks contemporaneously when fault trough subsidence set in. The graben sinking and shoulder uplift are still in progress. Rates of annual vertical movements up to 0.7 mm, as well as seismic activity, are observed. Below both graben and shoulders a cushion-shaped body has been ascertained, intercalated between crust and mantle, with P-velocities of 7.6–7.7 km s−1. This body is interpreted to be of mantle-derived material; its crest follows the graben axis and ascends up to 24 km beneath the graben floor. It is thought that rifting, like graben subsidence and shoulder elevation, is controlled by the formation and growth of this laccolithic body. Tensional tectonics and sideward plate movements are reduced to gravity slide of the torn and upwarped crustal plates or sub-plates, decoupled from the substratum by heat transfer and consequential partial melting along the cushion surface. The lateral offsets at the transitions from the Rhinegraben to its continual segments are intersected by transversal zones of enhanced seismicity and volcanic action. The observed fault patterns are interpreted as crustal traces of subcrustal transform faulting. Rhine graben tectonism is discussed as to its local interference and temporal interaction with Alpine orogenesis, just as in its causal and spatial connection to the world rift system as a whole, Several arguments pertaining to the understanding of the driving mechanisms are discussed and a new model of rift tectonics is indicated.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 1 (1974), S. 409-428 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This survey concerns mostly the theory of free oscillations, with a section on experimental work included at the end. Developments over the last 15 years are examined. The general theory of free oscillations is reviewed, and the effect on free oscillations of such factors as heterogeneity, the Earth's rotation and non-sphericity, and the source of the oscillations are discussed. Earth models, which have been obtained from oscillation data, are reviewed, and their use in forming theoretical seismograms is described.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 1 (1974), S. 429-458 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The earthquake magnitude was introduced into seismology nearly 40 yr ago, as a purely empirical concept. After an unparalleled success in scientific and practical applications the magnitude is developing into a concept with a clearer physical meaning and a more solid theoretical foundation. The magnitude determined from the maximum particle amplitude or velocity reflects the maximum radiation power of the seismic source in the frequency band recorded on a particular seismograph. Recently developed models for seismic sources assist in classifying earthquakes according to size and spectral character. From corresponding scaling laws the relations between various magnitude scales can be established. The magnitude aims at enabling one to compare the sizes of seismic sources ranging in character from nearly aseismic events to explosions. While the former are characterized by a relatively long-peroidic radiation maximum, the latter radiate primarily short-periodic seismic energy. Tectonic earthquakes are likely to range in character between the two extreme spectral cases. A comparison of earthquake magnitude with stellar magnitude leads to analogies in spectral character between earthquakes and stars, whereby seismic sources seem to follow a distribution similar to the Hertzsprung-Russell diagram for stars. Before seismological practice can catch up with the new cognitions, improvements in the definition of the earthquake magnitude are in need.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 10 (1989), S. 63-81 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Since the first discovery of silicate perovskites at high pressures and high temperatures in the laboratory in 1974, silicate perovskites have probably become the most studied materials in the geophysical community during the past decade or so and it is nearly established that these silicates are the most abundant materials making up the bulk of the Earth. There are basically two groups of silicate perovskites. Ferromagnesian silicates with or without Al2O3 crystallizing in a common orthorhombic perovskite structure at high pressures and temperatures (HPT) are preservable at ambient conditions. Silicates of large cations such as Ca and Na crystallizing in an ideal cubic perovskite structure at HPT cannot be preserved at ambient conditions. Thus, the lattice parameters, crystal structure, thermal expansion and compressional data have been studied, both experimentally and theoretically, mainly for orthorhombic silicate perovskites, and for MgSiO3 in particular. For MgSiO3 perovskite, the recommended lattice parameters area=4.777±0.003,b=4.931±0.003 andc=6.899±0.004 Å; bulk modulusB 0=2.4±0.2 Mbar; and volume thermal expansivity α=(3±1)×10−5 deg−1 at ambient conditions. Cubic CaSiO3 perovskite is probably less compressible than orthorhombic MgSiO3 perovskite. The lattice parameters of MgSiO3 perovskite increase linearly with increasing contents of both FeSiO3 and Al2O3, forming limited solid solutions. The degree of distortion of orthorhombic silicate perovskites does not appear to change at HPT.
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  • 8
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In two-component seismic observations with vertical and in-line horizontal geophones, the compressional (P-) wave amplitudes, as well as the vertically polarized shear (SV-) wave amplitudes, are observed on both vertical and horizontal geophones. In our case, we use a P-wave source, while the SV waves are the result of mode conversion. The mode-conversion mechanism considered here is related to the near-surface layers, i.e. we have a P-leg from the source and mode conversion at/in the weathered layer. The resulting SV waves therefore will show lateral variations because the elastic parameters of the near-surface layers vary along the seismic line, but these variations will be consistent at the surface. This effect is demonstrated by a synthetic example based on elastic parameters representative of the actual seismic line being considered. To separate the individual P and SV arrivals, we apply a two-dimensional convolution filter designed to meet the wavenumber-frequency (k-f) domain transfer function for P-SV separation which can be derived from thek-f domain geophone-receiving characteristic and the near surface P- and S-wave velocities. The reason for P-SV separation filtering in the offset-traveltime (X-T) domain instead of directly filtering in thek-f domain, is a great saving in computer time, asX-T filters, with few coefficients, can be used. In this paper, after a short summary of thek-f domain P-SV separation filters and their transformation to theX-T domain, we apply theX-T filters to synthetic data in order to demonstrate that our design is correct. We also work on actual data and discuss the problems being faced, which mainly, originate from the different geophone groups and, as a consequence, the different scalings of vertical and horizontal geophones. The main advantage of two-component seismic observations is two-fold: firstly, a clean P-wave section is obtained (SV-energy arriving at the receivers is cancelled by applying the foresaid separation filter) and, secondly we obtain an additional SV-wave section at almost no cost to data acquisition. These two sections contribute towards distinguishing between true and false bright spots, so they are, used as direct hydrocarbon indicator tools.
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  • 9
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We derive exact time-domain solutions for scattering of acoustic waves by a half plane by inverse Fourier transforming the frequency-domain integral solutions. The solutions consist of a direct term, a reflected term and two diffraction terms. The diffracting edge induces step function discontinuities in the direct and reflected, terms at two shadow boundries. At each boundary, the associated diffraction term reaches a maximum amplitude of half the geometrical optics term and has a signum function discontinuity so that the total field remains continuous. We evaluate solutions for practical point source configurations by numerically convolving the impulse diffraction responses with a wavelet. We solve the associated problems of convolution with a singular, truncated diffraction operator by analytically derived correction techniques. We produce a zero offset section and compare it to a Kirchhoff integral solution. Our exact diffraction hyperbola exhibits noticeable asymmetry, with higher amplitudes on the reflector side of the edge. Near the apex of the hyperbola the Kirchhoff solution approximates the exact diffraction term symmetric in amplitude about the reflection shadow boundary, but omits the other low amplitude term necessary to ensure continuity at the direct shadow boundary.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 10 (1989), S. 395-395 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
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