ALBERT

Description: Fluid dynamical simulations were carried out in order to investigate the effect of the large-scale mantle flow field and the depth of the plume source on the structure of the Iceland plume through time. The time-dependent location and shape of the plume in the Earth's mantle was calculated in a global model and it was refined in the upper mantle using a 3D Cartesian model box. Global flow was computed based on density heterogeneities derived from seismic tomography. Plate motion history served as a velocity boundary condition in both models. Hotspot tracks of the plume conduits and the plume head were calculated and compared to actual bathymetry of the North Atlantic. If a plume source in the lowermost mantle is assumed, the calculated surface position of the plume conduit has a southward component of motion due to southward flow in the lower mantle. Depending on tomography model, assumed plume age and buoyancy the southward component is more or less dominating. Plume models having a source at the 660 km discontinuity are only influenced by flow in the upper mantle and transition zone and hence rather yield westward hotspot motion. Many whole-mantle plume models result in a V-shaped track, which does not match the straight Greenland–Iceland–Faroe ridge. Models without strong southward motion, such as for a plume source at 660 km depth, match actual bathymetry better. Plume tracks were calculated from both plume conduits and plume heads. A plume head of 120 K anomalous temperature gives the best match between plume head track and bathymetry.

Description: Interlaboratory comparisons involving nine European stable isotope laboratories have shown that the routine methods of cellulose preparation resulted in data that generally agreed within the precision of the isotope ratio mass spectrometry (IRMS) method used: +/- 0.2% for carbon and +/- 0.3% for oxygen. For carbon, the results suggest that holocellulose is enriched up to 0.39% in C-13 relative to the purified alpha-cellulose. The comparisons of IRMS measurements of carbon on cellulose, sugars, and starches showed low deviations from -0.23 to +0.23% between laboratories. For oxygen, IRMS measurements varied between means from -0.39 to 0.58%, -0.89 to 0.42%, and -1.30 to 1.16% for celluloses, sugars, and starches, respectively. This can be explained by different effects arising from the use of low- or high-temperature pyrolysis and by the variation between laboratories in the procedures used for drying and storage of samples. The results of analyses of nonexchangeable hydrogen are very similar in means with standard deviations between individual methods from +/- 2.7 to +/- 4.9%. The use of a one-point calibration (IAEA-CH7) gave significant positive offsets in delta H-2 values up to 6%. Detailed analysis of the results allows us to make the following recommendations in order to increase quality and compatibility of the common data bank: (1) removal of a pretreatment with organic solvents, (2) a purification step with 17% sodium hydroxide solution during cellulose preparation procedure, (3) measurements of oxygen isotopes under an argon hood, (4) use of calibration standard materials, which are of similar nature to that of the measured samples, and (5) using a two-point calibration method for reliable result calculation.

Description: The aim of this work is the implementation of an effective Tsunami Early Warning System for the Indian Ocean. It is a component part of an Early Warning System that will also be capable of registering other natural disasters such as earthquakes and volcanic eruptions. The system integrates terrestrial observation networks of seismology und geodesy with marine measurements techniques and satellite observations. The required R & D work will be realized within the framework of a stage-plan, which will, within a short time span of 1-3 years, be able to provide effective warning on the one hand and, which will also allow for an integration of technological developments, currently undergoing further research. The initiative is coordinated by the Helmholtz Association of German Research Centres (HGF), represented by the GeoForschungsZentrum Potsdam (GFZ). In view of the geological situation one has to bear in mind that Indonesia especially, due to the fact that the main islands are located next to and above the Sunda seismogenic zone, could most frequently and most intensively in the future be prone to catastrophic Tsunami events. The envisaged Early Warning System for the Indian Ocean consists of different components as broadband seismometers, GPS, tide gauges, ocean-bottom pressure sensors and GPS-Buoys. On the basis of the data and recordings registered a warning can be generated. This presentation gives insight into the creation of the 26 December 2004 Tsunami, introduces the planned technical realization of the Early Warning System, shows first model scenarios and gives an overview of the planned realization of an Early Warning System in the Indian Ocean.

Description: The Vrancea region, in the Southeastern Carpathians (Romania), represents a unique case among the seismic areas in the world taking into account the extreme concentration and persistence of seismicity and the tectonic stress field. Subduction in a post-collisional phase is still active in a narrow area located at the sharp bend of the mountain belt. Our goal is to show that the particular shape of the shear-wave splitting can be interpreted in the light of the decoupling and slab-retreat processes, which hypothetically induce a specific configuration of the upper-mantle flow. Shear-wave splitting of SKS phases shows a relatively coherent pattern outside the epicentral area, suggesting a prominent NE-SW anisotropy, in agreement with previous estimations performed in Central and Eastern Europe and following the trends of the deformation field as outlined by the GPS measurements. A clear change is pointed out inside the Vrancea area, where strike-parallel polarization is emphasized. Toward the NW (wedge side), the polarization turns to a strike-perpendicular direction in agreement to an upwelling asthenospheric flow in the back-arc region (i.e., polarization aligned to the local strike of the slab). These shear-wave splitting attributes are not consistent with conventional models of 2-D mantle flow near subduction zones, nor with a sub-vertical down-dipping flow driven by the sinking of the slab. They correlate well with lateral inhomogeneities outlined by the tomography image, heat flow, seismic-wave attenuation and thermal field. We suggest that the eastward slab retreat, and decoupling between the underlying asthenosphere and the slab itself, have induced strike-parallel mantle flow, likely favoring detachment of the slab along the arcuate mountain belt. These processes are directly related to the strong anisotropy observed in the SE Carpathians. The anisotropy and GPS data suggest a strong coupling of the surface and mantle processes.

Description: Field-aligned currents (FACs) are an important mechanism for transporting energy and momentum from the solar wind into the upper atmosphere at high latitudes. The efficiency of energy dissipation depends on the ionospheric conductivity and the transverse scale size of the field-aligned current circuits. According to Vogt (2002) the conversion of electric current into heat should be most effective for scales of the order of some 10 km when typical ionospheric conductivities are considered. In order to test this conclusion we have performed a statistical analysis with FACs of various scale sizes. This study is based on observations that are derived from CHAMP magnetic field measurements taken during the years 2002-2005. FAC densities within the medium-scale wavelength band of 15-150 km and large-scale FACs (〉150 km) are considered separately and their distributions are compared. The thermospheric mass density recorded simultaneously by CHAMP is used as a measure for the heat deposited in the ionospheric E-layer. The relation between current strength of the two FAC types and thermospheric heating is determined in a superposed epoch analysis. The analysis is performed separately for each season and covers all local time sectors.