ALBERT

Beschreibung: A striking feature of Russian long-range seismic refraction data from Peaceful Nuclear Explosions is the observation of a high-frequency teleseismic P(tief)n, phase, which travels with a group velocity of 8.0 km s(hoch)-1 out to distances of several thousands of kilometres. Modelling using the reflectivity method shows that this phase can be understood as the response of an upper mantle that contains random RMS velocity fluctuations of about ±4 per cent superimposed on a positive velocity gradient. This class of model explains the existence of the teleseismic P(tief) n, its high-frequency content and its coda length. A teleseismic P(tief)n can only be generated if velocity flucluations are strong enough to cause multiple scattering and occur on a subwavelength scale. Cross-correlation properties of P- and S-wave velocity fluctuations exert a substantial influence on the wavefield. A completely unexpected phase can be observed if the fluctuations are imposed on a negative gradient

Beschreibung: For repeat pass SAR interferometry, two precision orbit products from ESA (processed at GFZ/D-PAF, Oberpfaffenhofen) are available: ERS-1/2.ORB.PRC"s and ERS-1/2.ORB.PRL"s. The conversion of interferogram phases to absolute surface heights require a relative baseline accuracy of 5 cm or even better. In a case study, the preliminary (PRL) and precise (PRC) orbits are used to derive DEMs. The results are compared with existing DTMs. In the test area in Thuringia (Germany), corner reflectors allow an additional accuracy assessment. The impact of orbit uncertainties on D-INSAR deformation analysis is less critical and the PRC"s already fulfill the accuracy demands. This is demonstrated by an example from the Dead Sea transform zone in Israel.

Beschreibung: Abstract: The micro structural development during nucleation and growth processes is studied numerically. Most of the studies are for the simple case of constant nucleation and growth rates, but a brief discussion is made of the effect of time-dependent nucleation and growth. A three dimensional code is used which accounts for not only the nucleation and growth of individual new grains, but also the effects of grain impingement, and which allows for the study of both homogeneous and heterogeneous nucleation. The microstructures are characterized by the grain size distribution (GSD) and the cluster size distribution (CSD), respectively. In the case of homogeneous nucleation, the development of GSD and CSD can be scaled using the Abram time taiga and Abram length delta_Av, which are related to the nucleation and growth rates. Both scaling constants have a simple physical meaning: the average grain size after the completion of the phase transformation is given by delta_Av, and the transformation half-time is approximately equal to taiga. The formation of a continuous chain of new phase grains (percolation transition) is observed at ~ 30 per cent transformation degree, and the geometry of the largest cluster near the percolation threshold has fractal characteristics with a fractal dimension of ~ 2.5. The presence of preferred sites of nucleation (heterogeneous nucleation), such as grain boundaries, significantly modifies the microstructures when the spacing of nucleation sites is much larger than the Abram length, the main effects being a reduced percolation threshold and an elongate grain shape. Some applications to the olivine-spinal transformation in subducting slabs and to the crystallization in a hypothetical magma ocean are discussed.

Beschreibung: GEOLIS (GFZ) ist ein innovativer Ansatz zum Aufbau einer Clearingstelle für die Lithosphärenforschung. Ziel ist der umfassende aktuelle Nachweis von weltweit verfügbaren geowissenschaftlich relevanten Informationsressourcen. Das Meta-Informationssystem GEOLIS (GFZ) verwaltet deskriptive (sekundäre) Daten über andere (primäre) Informationssysteme. Der operative Prototyp GEOLIS (GFZ) liefert eine Vorstellung davon, wie die Zukunft einer Geodaten-Infrastruktur aussehen könnte. Die offene Architektur besteht aus zwei Schichten: Die Integrationsplattform beinhaltet ein komplexes Datenmodell, das die verschiedenen Objekttypen zur Beschreibung (und Suche) beliebiger Informationsquellen bereitstellt. Die Anwendungsschicht umfaßt mehrere Werkzeuggruppen für das Informations-Management, die funktional unterschiedliche Schnittstellen zum System liefern. Dabei werden vier Gruppen von Service-Funktionen unterschieden: Information Broker, Navigator, GeoObjekt Modeler und Operator.

Beschreibung: Earthquake data collected by the INDEPTH-II Passive-Source Experiment show that there is a substantial south to north variation in the velocity structure of the crust beneath southern Tibet. North of the Zangbo suture, beneath the southern Lhasa block, a midcrustal low-velocity zone is revealed by inversion of receiver functions, Rayleigh-wave phase velocities, and modeling of the radial component of teleseismic P-waveforms. Conversely, to the south beneath the Tethyan Himalaya, no low-velocity zone was observed. The presence of the midcrustal low-velocity zone in the north implies that a partially molten layer is in the middle crust beneath the northern Yadong-Gulu rift and possibly much of southern Tibet.

Beschreibung: Variscan continent-continent collision in Central Europe was followed by a period of syn- to late-tectonic magmatism involving the extrusion of large volumes of Permosilesian-age volcanic rocks, particularly in the Northeast German Basin. The volcanic suite (up to ca. 2000 m thick) comprises rhyolites, acid and basic andesites, and tholeiitic and alkali basalts. Tectono-geochemical analysis, in conjunction with volume calculations and petrography reveals changes in volcanic activity over time. A total of five eruptive stages are recognised beginning in the Stephanian and extending up into the upper Rotliegend (Permian). These include; the Stephanian (Late Carboniferous) (andesite) pre-ignimbrite stage (I), lower Rotliegend (Permian)-age (explosive) ignimbrite stage (II), post-ignimbrite stage (III), late rhyolite stage (IV), and, upper Rotliegend (Permian)-age late basalt stage (V). In addition, several volcanic centres including at least two large caldera-like structures are recognised. The total calculated volume for the Northeast German Basin volcanics is ca 48,000 km (super 3) , comprising rhyolitic rocks and ignimbrites (ca. 70%), andesitic rocks (ca. 26%) and basalts with cogenetic dolerites (ca. 4%). Regional variations in composition and geochemistry are related to diverse crust-mantle regimes which correlate with differing positions relative to the heterogeneous basement of the Variscan foredeep or within the Rhenohercynian orogenic zone. The crustal thickening and increasing generation depth of the mafic magmas from north to south may reflect the presence of a pre-existing subduction-influenced basaltic magma source.

Beschreibung: This paper presents an updated interpretation of seismic anisotropy within the uppermost mantle of southern Germany. The dense network of reversed and crossing refraction profiles in this area made it possible to observe almost 900 traveltimes of the P(tief)n phase that could be effectively used in a time-term analysis to determine horizontal velocity distribution immediately below the Moho. For 12 crossing profiles, amplitude ratios of the P(tief)n phase compared to the dominant crustal phase were utilized to resolve azimuthally dependent velocity gradients with depth. A P-wave anisotropy of 3–4 per cent in a horizontal plane immediately below the Moho at a depth of 30 km, increasing to 11 per cent at a depth of 40 km, was determined. For the axis of the highest velocity of about 8.03 km s(hoch)-1 at a depth of 30 km a direction of N31°F was obtained. The azimuthal dependence of the observed P(tief)n amplitude is explained by an azimuth-dependent sub-Moho velocity gradient decreasing from 0.06 s(hoch)−1 in the fast direction to 0 s(hoch)−1 in the slow direction of horizontal P-wave velocity. From the seismic results in this study a petrological model suggesting a change of modal composition and percentage of oriented olivine with depth was derived.

Beschreibung: The 1985/86 series is revisited by modelling some pronounced features of the observed P waveforms frequently seen in the records of the CLL, BRG and the GRF seismograph stations. Travel times and waveforms can be explained by a simple two-layer crustal model consisting of an upper crust with V"SUB P" = 5.9 km/s and thickness t = 18 km, and a lower crust with V"SUB P" = 6.8 km/s and t = 11 km. The crust-mantle boundary is at 29 km depth. Waveforms recorded at distances between about 100 and 120 km consist of a low-amplitude first P wave which has travelled through the lower crust. This phase is followed about 0.5 to 1 s later by the large-amplitude main event. The focal depth of the main shock is constrained to 9 km. Depths of the stronger events (M"SUB L" 〉 3) of the swarm are within the depth range from 7 to 10 km. Inversion of body wave amplitudes and P wave polarities for the focal mechanism of the main events reveals a strike-slip mechanism which agrees well with previously published results.

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