ALBERT

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: We present a graphical user interface to facilitate the processing of teleseismic shear-wave splitting observations. In contrast to a fully automated technique, we present a manual, per-event approach that maintains user control during the sequence of processing. The SplitLab environment is intended to undertake the repetitive processing steps while enabling the user to focus on quality control and eventually the interpretation of the results. Pre-processing modules of SplitLab create a database of events and link the corresponding seismogram files. The seismogram viewer tool uses this database to perform the measurement interactively. Post-processing of the combined results of such a project includes a viewer and export option. Our emphasis lies in the application to teleseismic shear-wave splitting analysis, but our code can be extended easily for other purposes.

Description: Modern seismic networks can record high-quality digital data and transmit them back to a data-collection center in near real-time. This allows seismologists to monitor any ongoing seismic activity efficiently by determining the parameters of each earthquake, such as epicentral location and local magnitude. In addition, more recent developments during the last decade have made possible the inversion of regional waveforms for moment tensor derivation (e.g.. Ekström et al., 1998; Kao and Jian, 1999; Pondrelli et al., 2002). All such waveform processing can be performed fully automatically, giving scientists the opportunity to have a detailed picture of the seismicity in near real-time. The Greek region exhibits the highest seismicity in Europe and has experienced destructive earthquakes several times in the past (Papazachos and Papazachou, 1997). Therefore, it is particularly important to be able to monitor any seismic activity quickly and efficiently. The newly installed Hellenic broadband seismic network (HL) offers such capabilities by providing digital three-component waveform data recorded at 22 stations that cover the Greek region. This paper describes the network operation and routine waveform data processing, using as an example case the recent seismic unrest in the eastern Aegean Sea close to the Turkish coast. The analysis presented here also gives the first results on the spatial/temporal distribution of this seismic sequence and the faulting mechanism of 15 events with moment magnitudes between 3.9–5.6.

Description: Seismic anisotropy of the south Iberian upper mantle is investigated using shear-wave splitting of SKS phases. We analyzed teleseismic events recorded by sixteen permanent broadband stations installed on the southern Iberian Peninsula and in northern Africa, and we determined fast polarization directions ϕ, and delay times δt between fast and slow components. The area of investigation extends across two important geological structures in the Variscan Iberian Peninsula: the Variscan Iberian Massif in its center, and the Gibraltar arc in the Southeast, that represents the most westerly Alpine belt in the western Mediterranean. Shear-wave splitting measurements from stations in the Betic domain show homogeneous ENE–WSW fast directions nearly parallel to the trend of the mountain belt, and smooth spatial variations. Stations in the North, toward the southern part of the Variscan Iberian Massif show homogeneous fast directions however trending NS to NE–SW, different from those recorded in the Betic. These observations may reflect a post-Hercynian (Variscan) deformation of the Ossa-Morena zone, related to the main stages in the tectonic evolution of this part, namely transpressional stage, transtensional stage and shortening episode, or a deformation related to the posterior Alpine orogeny. Along the Gibraltar arc, we observe a smoothly varying ϕ trend changing from ENE–WSW in the Eastern Betics to NS in the area of Gibraltar and Ceuta, following more or less the general trend of the mountain belt around the Alboran Sea, and the coastline. Since a similar rotation is also visible in results from Pn anisotropy, this suggests that the anisotropy is vertically coherent starting from just below the Moho. Comparing the anisotropy pattern expected from various geodynamic models with the observed SKS splitting suggests that the anisotropy is best explained by a model of slab rollback, rather than by delamination models.

Description: Non-linear teleseismic bodywave tomography with data of the 1999 CALIXTO field experiment (Carpathian Arc Lithosphere X-Tomography) in Romania provides high-resolution imaging of the upper-mantle structure. In this paper, we present the relative P-wave velocity distribution of the lithosphere/asthenosphere system. Smearing from strong crustal velocity anomalies into the upper mantle is successfully suppressed by traveltime corrections with an a priori 3-D regional crustal velocity model (see Martin et al. 2005, herein referenced as paper 1). Our high-resolution image shows a high-velocity body beneath Vrancea and the Moesian platform with a NE–SW orientation between 70 and 200 km depth. Beneath 200 km a change in the orientation from NE–SW to N–S can be observed. The body reaches a maximum depth of about 350–370 km. The velocity perturbation is maximal between 110 and 150 km depth (5.2–5.8 per cent) and almost constant for depths beneath 200 km (3.2–3.8 per cent). As most authors of previous studies agree on Miocene subduction along the arc followed by soft continental collision we interpret the high-velocity body as the subducted, yet not fully detached slab. The NE-part of the slab appears to be mechanically coupled to the Moesian lithosphere and hosts the intermediate depth seismicity. In contrast the aseismic SW-part is interpreted as decoupled from the overlying lithosphere and torn off from the underlying lithospheric material beneath 200 km depth. Low velocity anomalies NW of the slab above 110 km depth are interpreted as a shallow asthenospheric upwelling. Further low-velocity anomalies are in agreement with a lithosphere-asthenosphere boundary at 110–150 km depth below the Moesian platform and deeper than 200 km under the East European platform (EEP). The tomographic images support models proposing slab rollback during subduction/collision, followed by slab steepening and lithospheric delamination. The different degrees of mechanical coupling of the slab to the overlying lithosphere allow to understand the loci of seismicity as volumes of stress concentration. Independent on the specifics of data interpretation our high-resolution image is a novel contribution to understand the process of ongoing lithospheric detachment associated with strong intermediate-depth seismicity in SE-Romania.

Description: Crustal and upper-mantle seismic discontinuities beneath eastern Turkey are imaged using teleseismic S-to-P converted phases. Three crustal phases are observed: the Moho with depth ranging between 30 and 55 km, indicating variable tectonic regimes within this continental collision zone; an upper-crustal discontinuity at approximately 10 km depth; and various crustal low-velocity zones, possibly associated with recent Quaternary volcanism. Imaging of the upper mantle is complicated by the 3-D geometry of the region, in particular due to the Bitlis–Zagros suture zone. However, several upper-mantle S-to-P converted phase are identified as being the signature of the lithosphere–asthenosphere boundary (LAB). The inferred LAB for the Eastern Anatolian Accretionary Complex indicates that eastern Turkey has an anomalously thin (between ∼60 and 80 km) lithosphere which is consistent with an oceanic slab detachment model. The observed LAB phases for the Arabian shield and Iranian plateau indicate that lithospheric thickness for these stable regions is on the order of 100 to 125 km thick, which is typical of continental margins.

Description: The International Federation of Digital Seismographic Networks (FDSN) is a non-governmental organization formed by institutions dedicated to seismological research and seismic monitoring. The FDSN is a successful complement to the International Seismological Centre (ISC) in pursuing a more than a century old tradition of global seismic data exchange. The main goal of the FDSN is the production and dissemination of seismic waveform data from high fidelity seismic observatories. The federation is formed by 65 organizations from 52 countries that contribute data to three main data centers in the United States, Europe, and Japan. A subset of the stations that conform the FDSN send real-time to the data management center (DMC) of the Incorporated Research Institutions of Seismology (IRIS) in the United States. Data from this real-time network is crucial to the determination of the seismic parameters of large earthquakes in a very short time after their occurrence and to support the efforts of institutions that are responsible for disaster relief or prevention. Most notably, tsunami warning centers use this information as a fundamental underpinning to issue warnings and alerts. The FDSN is an early participant of the global earth observation system of systems (GEOSS), contributing high-quality, timely and freely accessible seismic data. The purpose of this paper is to provide an overview of the FDSN from the viewpoint of an integrated system of observatories and to share with other GEOSS networks the successes, challenges and lessons learned by the FDSN in promoting the open and free access of seismological data for the benefit of scientific research and disaster prevention and mitigation.

Description: The objective of the TRANSALP project is an investigation of the Eastern Alps with regard to their deep structure and dynamic evolution. The core of the project is a 340-km-long seismic profile at 12°E between Munich and Venice. This paper deals with the P-wave velocity distribution as derived from active source travel time tomography. Our database consists of Vibroseis and explosion seismic travel times recorded at up to 100 seismological stations distributed in a 30-km-wide corridor along the profile. In order to derive a velocity and reflector model, we simultaneously inverted refractions and reflections using a derivative of a damped least squares approach for local earthquake tomography. 8000 travel time picks from dense Vibroseis recordings provide the basis for high resolution in the upper crust. Explosion seismic wide-angle reflection travel times constrain both deeper crustal velocities and structure of the crust–mantle boundary with low resolution. In the resulting model, the Adriatic crust shows significantly higher P-wave velocities than the European crust. The European Moho is dipping south at an angle of 7°. The Adriatic Moho dips north with a gentle inclination at shallower depths. This geometry suggests S-directed subduction. Azimuthal variations of the first-break velocities as well as observations of shear wave splitting reveal strong anisotropy in the Tauern Window. We explain this finding by foliations and laminations generated by lateral extrusion. Based on the P-wave model we also localized almost 100 local earthquakes recorded during the 2-month acquisition campaign in 1999. Seismicity patterns in the North seem related to the Inn valley shear zone, and to thrusting of Austroalpine units over European basement. The alignment of deep seismicity in the Trento-Vicenza region with the top of the Adriatic lower crust corroborates the suggestion of a deep thrust fault in the Southern Alps.

Description: Glacier surfaces are known to harbour abundant and active microbial communities. Phosphorus has been shown to be deficient in glacial environments, and thus is one of the limits on microbial growth and activity. We quantified the phosphorus pool in cryoconite debris and the concentration of dissolved phosphorus in supraglacial water on Werenskioldbreen, a Svalbard glacier. The mean total P content of the cryoconite debris was similar to 2.2 mg g(-1), which is significantly more than would be expected in rock debris from local sources. 57% of this P was present in the fraction defined as organic P. It may account for the P in excess of the rock debris, and could be explained by allochthonous input of organic matter. The concentration of total dissolved P in supraglacial water was very low (5.2-8.5 mu g l(-1)), which was probably caused by efficient flushing and re-adsorption onto mineral surfaces. Dissolved organic P (DOP) was a very important component of the dissolved phosphorus pool on Werenskioldbreen, as concentrations of DOP typically exceeded those of dissolved inorganic P (or SRP) by more than four times in all the glacial water types. It is very difficult to assess whether P was limiting in this environment solely on the basis of the N:P ratios in the debris or biomass. There may be some degree of biological control over the C:N:P ratios in the debris, but the phosphorus cycling in the supraglacial environment on this glacier seems to be mainly controlled by physical and geochemical processes.

Description: Hercynian basement rocks and Mesozoic ophiolites of the Calabria-Peloritani terrane drifted in the present position during the opening of western Mediterranean basins (namely Liguro-Provençal and Tyrrhenian basins) since the Oligocene. Basement rocks were partly involved by Alpine (late Cretaceous—Eocene) deformation and metamorphism before the onset of the drifting process. Even though the kinematics of the Alpine deformation in Calabria has been already defined, restoration of structural and kinematic data to the original position and orientation before the opening of the western Mediterranean has never been performed. In this work we present new structural and petrological data on a major tectonic contact of Alpine age exposed in central Calabria (Serre Massif). Structural and kinematic data are then restored at the original orientation in the early Oligocene time, to allow a correct tectonic interpretation. In the Serre Massif the Hercynian basement is sliced into three nappes emplaced during the Alpine orogeny. The upper nappe is formed by a nearly continuous section of the Hercynian crust, consisting of medium- to high-grade metamorphic rocks in the lower portion. The intermediate nappe mainly consists of orthogneisses, whereas the lower nappe is chiefly composed of phyllites. The contacts between the Alpine nappes are outlined by well developed mylonitic and cataclastic rocks. The Curinga-Girifalco Line is a well exposed shear zone that overprints mainly metapelitic rocks of the upper nappe and granitoid orthogneisses of the intermediate nappe. Mylonites of the intermediate nappe typically show overgrowths on garnet and hornblende with grossular-rich and tschermakitic composition, respectively. The Alpine mineral assemblage indicates that deformation took place in epidote-amphibolite facies at pressures ranging from 0.75 to 0.9 GPa. In the investigated area mylonites strike roughly WNW–ESE, with shallow dips towards SSW. Kinematic indicators in mylonites are mostly consistent with a top-to-the-SE shear sense in the present geographic coordinates. The mylonitic belt is affected by later extensional faults outlined by South-dipping cataclasite horizons. Published geochronological data indicate that mylonites and cataclasites developed in Eocene and early Miocene times, respectively. Considering rotational parameters coming from paleomagnetic studies and large-scale palinspastic reconstructions, the shear sense of the Curinga-Girifalco Line has been restored to the early Oligocene position and orientation. Through restoration a top-to-the-S shear sense is obtained. This result is in striking agreement with the convergence direction between Africa and W-Europe/Iberia during Eocene, computed from the North Atlantic magnetic anomalies. Our geodynamic reconstruction, combined with structural and petrological evidence, allows to relate the Curinga-Girifalco mylonites to a thrust related to the southeastern front of the double-verging Alpine chain. The adopted method could be used also for other exotic terranes, such as the Kabylie or the Corsica-Sardinia, to better constrain geometry and evolution of the southern Alpine belt.

Description: In this study, we measure the interseismic deformation across the western Haiyuanfault. This fault is a major left-lateral fault at the north-eastern edge of the Tibetanplateau. Our aim is to better constrain its present mechanical behavior, at the originof two M ̃8 earthquakes in 1920 and 1927, and along which a seismic gap with highpotential seismic hazard has been identified. The gap is covered by ERS and Envisatdata along three adjacent tracks. Along the two easternmost tracks, a steep velocitygradient has been observed across the fault, consistent with a left-lateral slip at a rateof 6.3 ́s2 mm/yr below a small apparent locking depth (〈2 km), which may be in-dicative of transient superficial creep or related to a weak fault zone (Cavalié et al.2008). The western track has not yet been studied as it covers a very high mountain-ous area, which introduces strong geometrical decorrelation. In this study, we focuson this track and propose a new InSAR adaptive range filter algorithm. Generally, therange interferometric filter assumes a constant slope terrain and the new generation offilters, even if they shift bandwidth with respect to the terrain slope, perform a spectralcul for the whole range line. In our approach, a sliding moving window is used to per-form a local adaptive range filter. Areas over critical baseline and shadowed areas for example can be detected and masked with this approach. During the process, an op-timisation is performed to perfectly align the local common bandwidths. Preliminaryresults show an improvement of the coherence over mountainous area under study,making it possible to exploit the InSAR data archive in this area.

Description: In this study, we measure the interseismic deformation across the western Haiyuanfault. This fault is a major left-lateral fault at the north-eastern edge of the Tibetanplateau. Our aim is to better constrain its present mechanical behavior, at the originof two M ̃8 earthquakes in 1920 and 1927, and along which a seismic gap with highpotential seismic hazard has been identified. The gap is covered by ERS and Envisatdata along three adjacent tracks. Along the two easternmost tracks, a steep velocitygradient has been observed across the fault, consistent with a left-lateral slip at a rateof 6.3 ́s2 mm/yr below a small apparent locking depth (〈2 km), which may be in-dicative of transient superficial creep or related to a weak fault zone (Cavalié et al.2008). The western track has not yet been studied as it covers a very high mountain-ous area, which introduces strong geometrical decorrelation. In this study, we focuson this track and propose a new InSAR adaptive range filter algorithm. Generally, therange interferometric filter assumes a constant slope terrain and the new generation offilters, even if they shift bandwidth with respect to the terrain slope, perform a spectralcul for the whole range line. In our approach, a sliding moving window is used to per-form a local adaptive range filter. Areas over critical baseline and shadowed areas for example can be detected and masked with this approach. During the process, an op-timisation is performed to perfectly align the local common bandwidths. Preliminaryresults show an improvement of the coherence over mountainous area under study,making it possible to exploit the InSAR data archive in this area.

Description: Shear-wave splitting analyses have been carried out on teleseismic data from the southwest of Ireland acquired during the Irish Seismological Lithospheric Experiment (ISLE). The data were gathered over a ten-month period by a temporary network of 23 broadband and short-period stations. The results are compared with data from two permanent broadband seismic stations, which have recorded SKS and SKKS phases for up to 10 years. The purpose of the experiment was to investigate possible anisotropy within the crust and mantle related to Caledonian deformation. Here we report splitting results which show an average delay time of 1.2 s and a variation of fast-polarisation direction with back azimuth that surprisingly suggests a much deeper origin for anisotropy than was anticipated.

Description: Fluctuations in the length of day (Δlod) can be caused by temporal variations of the inertia tensor described by the excitation function and by disturbances of the torque balance between core and mantle. Recent models of the atmospheric excitation of the variations of the lod certainly failed with respect to longer periods (e.g., at about 70 years), but seem to be responsible for the annual period, the 22 years period and for a part of the nearly 30 years period. So, another geophysical phenomenon is needed which is responsible for the remaining part of unexplained lod variations. Previous studies of the geomagnetic core-mantle coupling were re-examined using lod values from which atmospherically excited parts were removed. The remaining part of the 30 years period could be explained by core-mantle coupling. Additionally, the torque blance was realized by assuming lower values of the electrical conductivity at the bottom of the mantle. It was concluded that the consideration of geophysical processes within atmosphere and hydrosphere will be important for future refinements of the core-mantle coupling models of the decade fluctuations in the lod.

Description: The striking improvements in long- to medium-wavelengths gravity field recovery achieved with GPS-CHAMP and GPS-GRACE high-low and GRACE K-band range low-low satellite-to-satellite tracking prompted us to combine the satellite data with surface data from altimetry over the oceans and gravimetry over the continents to generate a new, high resolution global gravity field model: EIGEN-CG01C. The model is complete to degree/order 360 in terms of spherical harmonics and resolves half-wavelengths of 55 km in the geoid and gravity anomaly fields. A special band-limited combination method has been applied in order to preserve the high accuracy from the satellite data in the lower frequency band of the geopotential and to allow for a smooth transition to the high-frequency band, dominated by the surface data. Compared to pre-CHAMP/GRACE global high-resolution gravity field models, the accuracy was improved by one order of magnitude to 4 cm and 0.5 mgal in terms of geoid heights and gravity anomalies, respectively, at a spatial resolution of 200 km half-wavelength. The overall accuracy at degree/order 360 is estimated to be 20 cm and 5 mgal, respectively, and benefits significantly from recently released new gravity anomaly compilations over the polar regions. In general, the accuracy over the oceans is better than over the continents reflecting the higher quality of the available surface data.

Description: Seismic monitoring in Romania has more than 100 years of tradition. In spite of the World wars and critical periods, these activities progressed and have a good future. Presently a complex and high dynamic range real time seismic network ensures the seismic monitoring in Romania. A huge seismic database became a strong support for research and investigation in seismic field of activity. This insures a constant seismic data exchange with the global seismic monitoring systems. International collaboration is established with important scientific entities around of the world. There is a planning for a future upgrade of the National Seismic Network with more broadband seismic stations. Infrasound research project, as complementary activity for Romanian seismic monitoring, will start also.

Description: Die Bundesregierung beauftragte die Helmholtz-Gemeinschaft, vertreten durch das GFZ, mit der Entwicklung eines Tsunami-Frühwarnsystems für den indischen Ozean. Seit dem 11. November ist das System offiziell im Betrieb. Projektleiter Jörn Lauterjung stellte sich den Fragen der „GeoForschungs-Zeitung“.

Description: Seismological studies generally suggest that the Earth’s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth. Previous body-wave studies of the inner core have relied on ray tracing or waveform modeling using one-dimensional (1D) models. Here we present non-linear tomographic inversions of the inner core anisotropy using three-dimensional (3D) ray tracing, spline parameterization, and a large collection of PKP differential travel times. We adapt a pseudo-bending ray tracing (PBR) method in spherical coordinates for seismic rays that traverse the inner core (PKP(DF) phase). The method iteratively perturbs each discontinuity point and continuous segment of the ray through 3D earth structure so that its travel time is minimum. The 3D anisotropic structure of the inner core is approximated to the first order as 3D heterogeneous (but isotropic) structure for a given ray. The data are corrected using a scaled mantle tomographic model. The inner core anisotropy model obtained has the following major features. (1) The model has strong hemispherical and depth variation. The isotropic velocity in the topmost inner core is greater in quasi-eastern hemisphere (QEH) (40–160°E) than in quasi-western hemisphere (QWH) (other longitudes). The anisotropy is weak in QEH to the depth of 600–700 km below the inner core boundary (ICB), while in QWH, the anisotropy increases at much shallower depth (about 100–200 km below the ICB) to about 3–4%, then remains at about 2–4% throughout the rest of the inner core. (2) The anisotropy form changes abruptly (over a depth range of about 150 km) at the radius of about 600 km, slightly less than half of the inner core radius, forming a distinct inner inner core (IIC). The velocity in the IIC has maximums at equatorial and polar directions and minimum at an angle of about 40° from the equatorial plane. The velocity in the outer inner core (OIC), however, changes little for ray directions 0–40° from the equatorial plane. (3) Despite large variation of the anisotropy, the isotropic velocity (Voigt average) throughout the inner core is nearly uniform. The results suggest that the OIC is likely composed of the same type of iron crystals with uniform chemistry, but the IIC may be composed of a different type of crystal alignment, a different iron phase, or a different chemical composition. Our tests on model parameterization, mantle correction, and linear and non-linear inversion suggest the main features of our model are very robust. However, fine scale structures are likely to differ, particularly in the major transition zones, e.g., in the topmost QWH (isotropy to anisotropy), between OIC and IIC (change in the form of anisotropy), and between QEH and QWH in OIC (difference in anisotropy strength). Searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful.

Description: We investigate the geometry of deep subduction zone waveguides (depth 〉100 km). The wavefield characteristics for up-dip profiles are described and compared with data recorded at the Chile–Peru subduction zone. Observed distorted P onsets at stations in northern Chile near 21°S can be matched by 2-D finite difference simulations of a thin low-velocity layer (LVL) atop the slab in an IASP91 velocity model. The replacement of the LVL by simple random velocity undulations in the slab in the same model cannot explain the observations. Varying slab geometries are investigated and the distribution of guided wave onsets originating in deep waveguides is predicted relative to the slab surface. Further, double couple source position and orientation is explored and found to be closely limited by the guided wave observations. Sources situated above the layer and at distances more than 2 layer widths below the subducted Moho are not suitable. For the remaining favourable source locations, a strong link between pulse shapes and fault plane dip angle is evident. We conclude that up-dip guided wave observations at subduction zones follow a simple pattern given by slab geometry and modified by source position. The resulting onsets are shaped by layer thickness and velocity contrast and further influenced by the shape of the slab surface.

Description: Warum gleiten die Pazifische und die Nordamerikanische Platte in Mittelkalifornien einfach aneinander vorbei, während sie in den Ballungsgebieten von Los Angelos und San Francisco katastrophale Erdbeben verursachen? Um den Erdbeben auf den Grund zu gehen, errichteten Wissenschaftler der „Stanford Universität“ und des „US Geological Survey“ das San Andreas Tiefenobservatorium (SAFOD). Im Rahmen eines ICDP Projektes durchbohrten sie 2007 den Erdbebenherd in einer Tiefe von 2500 Meter. Parallel zu dieser Bohrung führte der GFZ-Mitarbeiter Michael Becken zusammen mit der Arbeitsgruppe Magnetotellurik großflächige geophysikalische Untersuchungen an der San Andreas Störung durch.

Description: This thesis focuses on the seismic structure of the lithosphere and upper mantle beneath the western Eger Rift area with the aim of investigating deep-lying possible causes of the phenomena observed at surface. For the investigation, data of the international passive seismic experiment BOHEMA carried out in 2002/2003 was used. The BOHEMA network consisted of 61 permanent and 84 temporary stations and was centred on the western Eger Rift. The resulting large data set allowed a high resolution P and S receiver function study using P-to-S and S-to-P converted waves, respectively, to map seismic discontinuities in the lithosphere and upper mantle. Data from an earlier passive seismic experiment was additionally used to complement the BOHEMA data set. The results of the analysis are described in this thesis ‘from top to bottom’. [...] Furthermore, the first map of average crustal vp/vs ratios is presented for the investigated area.

Description: Im Jahr 2016 soll er fertig gestellt sein: der Gotthard-Basistunnel. Mit 57 Kilometern wird er dann der längste und modernste Tunnel der Welt sein. Ein Projekt der Superlative. Grund genug für den Verein der „Freunde und Förderer des GFZ“ (FFGFZ), diesem Großprojekt auf einer Exkursion einen Besuch abzustatten. Am 22. Oktober konnten zwölf Mitglieder des Vereins die Arbeiten mit der Tunnelbohrmaschine der Firma Herrenknecht vor Ort erleben.

Description: Oceanic microseisms are small oscillations of the ground, in the frequency range of 0.05–0.3 Hz, associated with the occurrence of energetic ocean waves of half the corresponding frequency. In 1950, Longuet-Higgins suggested in a landmark theoretical paper that (i) microseisms originate from surface pressure oscillations caused by the interaction between oppositely travelling components with the same frequency in the ocean wave spectrum, (ii) these pressure oscillations generate seismic Stoneley waves on the ocean bottom, and (iii) when the ocean depth is comparable with the acoustic wavelength in water, compressibility must be considered. The efficiency of microseism generation thus depends on both the wave frequency and the depth of water. While the theory provided an estimate of the magnitude of the corresponding microseisms in a compressible ocean, its predictions of microseism amplitude heretofore have never been tested quantitatively. In this paper, we show a strong agreement between observed microseism and calculated amplitudes obtained by applying Longuet-Higgins' theory to hindcast ocean wave spectra from the North Atlantic Ocean. The calculated vertical displacements are compared with seismic data collected at stations in North America, Greenland, Iceland and Europe. This modelling identifies a particularly energetic source area stretching from the Labrador Sea to south of Iceland, where wind patterns are especially conducive to generating oppositely travelling waves of same period, and the ocean depth is favourable for efficient microseism generation through the ‘organ pipe’ resonance of the compression waves, as predicted by the theory. This correspondence between observations and the model predictions demonstrates that deep ocean nonlinear wave–wave interactions are sufficiently energetic to account for much of the observed seismic amplitudes in North America, Greenland and Iceland.

Description: Cryoconite holes are unique freshwater environments on glacier surfaces, formed when solar-heated dark debris melts down into the ice. Active photoautotrophic microorganisms are abundant within the holes and fix inorganic carbon due to the availability of liquid water and solar radiation. Cryoconite holes are potentially important sources of organic carbon to the glacial ecosystem, but the relative magnitudes of autochthonous microbial primary production and wind-borne allochthonous organic matter brought are unknown. Here, we compare an estimate of annual microbial primary production in 2006 on Werenskioldbreen, a Svalbard glacier, with the organic carbon content of cryoconite debris. There is a great disparity between annual primary production (4.3 mu g C g(-1) year(-1)) and the high content of organic carbon within the debris (1.7-4.5%, equivalent to 8500-22 000 mu g C g(-1) debris). Long-term accumulation of autochthonous organic matter is considered unlikely due to ablation dynamics and the surface hydrology of the glacier. Rather, it is more likely that the majority of the organic matter on Werenskioldbreen is allochthonous. Hence, although glacier surfaces can be a significant source of organic carbon for glacial environments on Svalbard, they may be reservoirs rather than oases of high productivity.

Description: Digitale Forschungsdaten sind sowohl unverzichtbare Basis als auch Resultat der wissenschaftlichen Arbeit. Jede Disziplin hat ihre eigenen technischen und inhaltlichen Ansprüche und Vorstellungen, so dass eine Vielfalt von Formate und Medientypen als Forschungsdaten vorkommen: von Meßdatentabellen im ASCII-Format bis hin zu interaktiven 3D-Modellen. Allen ist aber gemeinsam, dass sie eine wertvolle, jedoch schwierig zu managende Ressource darstellen. In diesem Vortrag werden Strategien vorgestellt und diskutiert, wie das Management von Forschungsdaten besser gestaltet und wissenschaftliche Arbeitsabläufe unterstützt werden können, ohne dabei eine "Datenmanagement-Bürokratie" aufzubauen.

Description: A temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike-slip Liquiñe-Ofqui fault zone (LOFZ) in southern Chile. Seventy five shallow crustal events with magnitudes up to M(tief)w 3.8 and depths shallower than 25 km were observed in an 11-month period mainly occurring in different clusters. Those clusters are spatially related to the LOFZ, to the volcanoes Chaitén, Michinmahuida and Corcovado, and to active faulting on secondary faults. Further activity along the LOFZ is indicated by individual events located in direct vicinity of the surface expression of the LOFZ. Focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike-slip mechanisms indicating a NE–SW direction of the P-axis for the LOFZ at this latitude. The seismic activity reveals the present-day activity of the fault zone. The recent M(tief)w 6.2 event near Puerto Aysén, Southern Chile at 45.4°S on April 21, 2007 shows that the LOFZ is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region.

Description: Der Themenband vereinigt ausgewählte Forschungsergebnisse zum Risikomanagement extremer Hochwasserereignisse. In der vom BMBF initiierten Förderaktivität konnten neben herausragenden Hochwassern der letzten Jahrzehnte auch sehr seltene Abflussereignisse vor 1900 untersucht werden. Zunächst werden die vorrangig in Archiven lagernden wasserwirtschaftlich/wasserbaulich relevanten Altunterlagen sowie meteorologische und hydrologische Datensätze vorgestellt und geeignete Methoden zu deren Erhebung und kritischen Bewertung näher erläutert. Anschließend wird anhand von Fallbeispielen aufgezeigt, wie hinlänglich gesicherte historische Quellenbefunde erfolgreich in aktuelle Analysen integriert werden können. Hierzu gehören sowohl die Rekonstruktion hochwasserrelevanter Wetterlagen am Beispiel des Neckarhochwassers von 1824 als auch die hydraulische Modellierung historischer Hochwasserereignisse sowie statistische Analysen zur Häufigkeit schwerer Hochwasser der Elbe.

Description: The deep structure of the upper mantle is determined from data on phase velocities of Love and Rayleigh waves measured by a differential method on traces between two stations in central Western Europe. One-dimensional velocity structures are first constructed from data of each pair of stations, after which two-dimensional distributions of SH and SV velocities are calculated by the method of two-dimensional tomography from S wave velocities at fixed depths. The results are presented in the form of 2-D vertical structures of the average S wave velocity (S = (SV + SH)/2) constructed along profiles crossing the region in directions of the best resolution. The main structural features are a higher velocity zone at depths of 60–80 km in the area (48°–50°N, 9°–11°E) and a lower velocity zone in the western part of the region at depths of 100–150 km, probably extending farther beyond the studied area

Description: For derived flood frequency analysis based on hydrological modelling long continuous precipitation time series with high temporal resolution are needed. Often, the observation network with recording rainfall gauges is poor, especially regarding the limited length of the available rainfall time series. Stochastic precipitation synthesis is a good alternative either to extend or to regionalise rainfall series to provide adequate input for long-term rainfall-runoff modelling with subsequent estimation of design floods. Here, a new two step procedure for stochastic synthesis of continuous hourly space-time rainfall is proposed and tested for the extension of short observed precipitation time series. First, a single-site alternating renewal model is presented to simulate independent hourly precipitation time series for several locations. The alternating renewal model describes wet spell durations, dry spell durations and wet spell intensities using univariate frequency distributions separately for two seasons. The dependence between wet spell intensity and duration is accounted for by 2-copulas. For disaggregation of the wet spells into hourly intensities a predefined profile is used. In the second step a multi-site resampling procedure is applied on the synthetic point rainfall event series to reproduce the spatial dependence structure of rainfall. Resampling is carried out successively on all synthetic event series using simulated annealing with an objective function considering three bivariate spatial rainfall characteristics. In a case study synthetic precipitation is generated for some locations with short observation records in two mesoscale catchments of the Bode river basin located in northern Germany. The synthetic rainfall data are then applied for derived flood frequency analysis using the hydrological model HEC-HMS. The results show good performance in reproducing average and extreme rainfall characteristics as well as in reproducing observed flood frequencies. The presented model has the potential to be used for ungauged locations through regionalisation of the model parameters.

Description: In order to determine the links between geochemical parameters controlling the formation of silica sinter in hot springs and their associated microbial diversity, a detailed characterisation of the waters and of in situ-grown silica sinters was combined with molecular phylogenetic analyses of the bacteria] communities in Icelandic geothermal environments. At all but one site, the microorganisms clearly affected, and in part controlled, the formation of the macroscopic textures and structures of silica sinter edifices. In addition, the class and genera level phylogenetic diversity and distribution appeared to be closely linked to variations in temperature, salinity and pH regimes.

Description: A new model of the three-dimensional shear velocity structure of the Africa-Eurasia plate boundary is presented. The new model is derived by jointly inverting different types of seismic data. The two main sources of information are regional waveforms and teleseismic S wave arrival times. We show that it is possible to find a model that fit the different data types nearly as well as when inverting solely one type of data. The main improvement in resolving power is achieved between depths of 300 and 700 km, though the improvements are not limited to this depth range. Our model reflects the complicated evolution of this plate boundary area. The transition zone is dominated by high-velocity anomalies which we infer to represent a mix of lithosphere that subducted relatively recently or is not sufficiently cold and dense to traverse the 660-km discontinuity. The only low-velocity zone in the transition zone is beneath the Ionian Sea. The high-velocity Hellenic slab is continuous throughout the upper mantle and into the lower mantle to about 1200 km, most likely representing subducted Neo-Tethys lithosphere. The uppermost mantle is dominated by low velocities, consistent with the high level of tectonic activity. Low-velocity regions are relatively strong beneath the Mid-Atlantic Ridge, Turkey, and the Dead Sea region. The region's current lithosphere is relatively thin, except beneath the Adriatic and Ionian seas and the easternmost Atlantic Ocean.

Description: The Iberian Peninsula and the Maghreb experience moderate earthquake activity and oblique, ∼ NW–SE convergence between Africa and Eurasia at a rate of ∼ 5 mm/yr. Coeval extension in the Alboran Basin and a N35°E trending band of active, left-lateral shear deformation in the Alboran–Betic region are not straightforward to understand in the context of regional shortening, and evidence complexity of deformation at the plate contact. We estimate 86 seismic moment tensors (MW 3.3 to 6.9) from time domain inversion of near-regional waveforms in an intermediate period band. Those and previous moment tensors are used to describe regional faulting style and calculate average stress tensors. The solutions associated to the Trans-Alboran shear zone show predominantly strike-slip faulting, and indicate a clockwise rotation of the largest principal stress orientation compared to the regional convergence direction (σ1 at N350°E). At the N-Algerian and SW-Iberian margins, reverse faulting solutions dominate, corresponding to N350°E and N310°E compression, respectively. Over most of the Betic range and intraplate Iberia, we observe predominately normal faulting, and WSW–ENE extension (σ3 at N240°E). From GPS observations we estimate that more than 3 mm/yr of African (Nubian)–Eurasian plate convergence are currently accommodated at the N-Algerian margin, ∼ 2 mm/yr in the Moroccan Atlas, and ∼ 2 mm/yr at the SW-Iberian margin. 2 mm/yr is a reasonable estimate for convergence within the Alboran region, while Alboran extension can be quantified as ∼ 2.5 mm/yr along the stretching direction (N240°E). Superposition of both motions explains the observed left-lateral transtensional regime in the Trans-Alboran shear zone. Two potential driving mechanisms of differential motion of the Alboran–Betic–Gibraltar domain may coexist in the region: a secondary stress source other than plate convergence, related to regional-scale dynamic processes in the upper mantle of the Alboran region, as well as drag from the continental-scale motion of the Nubian plate along the southern limit of the region. In the Atlantic Ocean, the ∼ 3.5 mm/yr, westward motion of the Gibraltar Arc relative to intraplate Iberia can be accommodated at the transpressive SW-Iberian margin, while available GPS observations do not support an active subduction process in this area.

Description: An extensive analysis of multiple ScS reverberation data sets sampling regions of active or recent subduction reveals evidence of midmantle reflections apparently stemming from fragments of subducted slabs or from the interaction between subducted slabs and the surrounding mantle. Transition zone reflectors are detected beneath the southwest Pacific Ocean and Melanesia with mean depths of ∼850 and 1100 km in the majority of source–receiver corridors crossing the study area. The observations are most spatially coherent beneath the Coral and Tasman Seas. Coincident observations of the two reflectors along most seismic corridors suggests (but does not mandate) the existence of two distinct reflectors rather than bimodal depth distribution of a single reflector or distributed scatterers. Beneath North America, reflectors at depths of ∼1380 and 1530 km are seen in the midcontinent region; further east, the reflections are shallower, with depths near 940 and 1130 km. Unlike the southwest Pacific, the reflectors are not paired in any of the individual source–receiver corridors. This and the depth variability of the observations indicate that the reflector (or reflectors) in the Americas is (are) fragmented from west to east (transecting source–receiver corridors). The impedance contrasts of these features rival that of the 660-km discontinuity, suggesting that individual fragments of the reflecting surfaces must be relatively continuous and flat from north to south (along individual corridors) to maintain a strong apparent impedance contrast. The reflections in both study areas are unlikely to be the result of slabs interacting with a chemical boundary layer or small-scale scatterers within the midmantle. More likely these reflectors result from a pressure–temperature-dependent phase transition within or around subducting slabs.

Description: Productivity in the Southern Oceans is iron-limited, and the supply of iron dissolved from aeolian dust is believed to be the main source from outside the marine reservoir. Glacial sediment sources of iron have rarely been considered, as the iron has been assumed to be inert and non-bioavailable. This study demonstrates the presence of potentially bioavailable Fe as ferrihydrite and goethite in nanoparticulate clusters, in sediments collected from icebergs in the Southern Ocean and glaciers on the Antarctic landmass. Nanoparticles in ice can be transported by icebergs away from coastal regions in the Southern Ocean, enabling melting to release bioavailable Fe to the open ocean. The abundance of nanoparticulate iron has been measured by an ascorbate extraction. This data indicates that the fluxes of bioavailable iron supplied to the Southern Ocean from aeolian dust (0.01-0.13 Tg yr(-1)) and icebergs (0.06-0.12 Tg yr(-1)) are comparable. Increases in iceberg production thus have the capacity to increase productivity and this newly identified negative feedback may help to mitigate fossil fuel emissions.

Description: Presented here are quantitative dissolution rate data (Volume of pyrite lost/time) for the inorganic oxidation of pyrite in synthetic, anaerobic and acidic (pH 2) hydrothermal vent fluids (HVF) from experiments where the volume toss was measured directly via Vertical Scanning Interferometry (VSI). The VSI-derived reaction rate was 2.12 x 10(-10) +/- 1.14 x 10(-11) mol/m(2)/min, which is similar to 2 to 4 orders of magnitude slower than pyrite oxidation rates previously determined using traditional batch experiments where rates are calculated based on changes in Solution chemistry. This lower rate stems primarily from differences in experimental conditions (i.e. water to rock ratios, vigorous vs. gentle stir rates, grain-size effects, time), yet the rates derived here are believed to be more representative of pyrite oxidation in natural environments where more static and high solution to solid rate conditions prevail, such as seafloor conditions or acid-mine-drainage environments.

Description: Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected.We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is locatedNEof the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal highconductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF.We further infer from the MT model that the resistive Salinian block basement to the SW of the SAFOD represents an isolated body, being 5–8 km wide and reaching to depths 〉7 km, in agreement with aeromagnetic data. This body is separated from a massive block of Salinian crust farther to the SW. The NE terminus of resistive Salinian crust has a spatial relationship with a near-vertical zone of increased seismic reflectivity ∼15 km SW of the SAF and likely represents a deep-reaching fault zone.

Description: A new three-dimensional seismic model and relocated regional seismicity are used to illuminate the great Sumatra-Andaman Islands earthquake of December 26, 2004. The earthquake initiated where the incoming Indian Plate lithosphere is warmest and the dip of the Wadati-Benioff zone is least steep along the subduction zone extending from the Andaman Trench to the Java Trench. Anomalously high temperatures are observed in the supra-slab mantle wedge in the Andaman back-arc. The subducting slab is observed along the entire plate boundary to a depth of at least 200 km. These factors contribute to the location of the initiation of rupture, the strength of seismic coupling, the differential rupture properties between the northern and southern segments of the earthquake, and the cause of convergence in the Andaman segment.

Description: The reduction of information contained in model time series through the use of aggregating statistical measures is very high compared to the amount of information that one would like to draw from it for model identification and calibration purposes. Applied within a model identification context, aggregating statistical performance measures are inadequate to capture details on time series characteristics. It has been readily shown that this loss of information on the residuals imposes important limitations on model identification and -diagnostics and thus constitutes an element of the overall model uncertainty. In this contribution we present an approach using a Self-Organizing Map (SOM) to circumvent the identifiability problem induced by the low discriminatory power of aggregating performance measures. Instead, a Self-Organizing Map is used to differentiate the spectrum of model realizations, obtained from Monte-Carlo simulations with a distributed conceptual watershed model, based on the recognition of different patterns in time series. Further, the SOM is used instead of a classical optimization algorithm to identify the model realizations among the Monte-Carlo simulations that most closely approximate the pattern of the measured discharge time series. The results are analyzed and compared with the manually calibrated model as well as with the results of the Shuffled Complex Evolution algorithm (SCE-UA).

Description: Global mapping of 410 and 660 km discontinuity topography and transition zone thickness has proven to be a powerful tool for constraining mantle chemistry, dynamics and mineralogy. Numerous seismic and mineral physics studies suggest that the 410 km discontinuity results from the phase change of olivine to wadsleyite and the 660 km discontinuity results from the phase change of ringwoodite to perovskite and magnesiowustite. Underside reflections of the 410 and 660 km discontinuities arrive as precursors to SS. With the recent development of a semi-automated method of determining SS arrivals, we have more than tripled the Flanagan and Shearer (1998a) data set of handpicked SS waveforms. We are able to increase resolution by stacking waveforms in 5° rather than 10° radius bins as well as increasing data coverage significantly in the southern hemisphere. The resulting SS-S410S and SS-S660S times are heavily influenced by upper-mantle velocity structure. We perform a joint inversion for discontinuity topography and velocity heterogeneity as well as performing a simple velocity correction to the precursor differential times and find little difference between the two methods. The 660 km discontinuity topography and transition zone thickness are correlated with velocities in the transition zone whereas the 410 km discontinuity topography is not. In addition, the 410 km discontinuity topography is not correlated with the 660 km discontinuity topography, rather anticorrelated, as expected due to the opposite signs of the Clapeyron slopes of their respective phase changes. These results suggest that, whereas the topography of 660 km discontinuity could be dominated by thermal effects, the topography of the 410 km discontinuity is likely dominated by compositional effects. In addition, unlike previous studies which find less topography on the 410 km discontinuity than on the 660 km discontinuity, our 410 and 660 km topography have similar amplitudes.

Description: The nucleation and growth of silica nanoparticles in supersaturated geothermal waters was simulated using a flow-through geothermal simulator system. The effect of silica concentration ([SiO2]), ionic strength (IS), temperature (T) and organic additives on the size and polydispersity of the forming silica nanoparticles was quantified. A decrease in temperature (58 to 33 degrees C) and the addition of glucose restricted particle growth to sizes 〈20 mm, while varying [SiO2] or IS did not affect the size (30-35 nm) and polydispersity (+/- 9 nm) observed at 58 degrees C. Conversely, the addition of xanthan gum induced the development of thin films that enhanced silica aggregation.

Description: Am Beispiel des Magnetits und Hämatits wird der Einfluß eines homogenen Magnetfeldes auf Wachstum und Orientierung untersucht. Die Kristalle wurden mit Hilfe chemischer Transportreaktionen bei 500 °с und Feldstärken von О - 4000 Ое gezüchtet. Magnetfelder dieser Stärke üben auf Wachstum und Orientierung beider Mineralien keinen Einfluß aus. Die experimentellen Ergebnisse werden im Hinblick auf das magnetische Verhalten kleiner Teilchen diskutiert. Dabei zeigt sich, daß die Kristallite bereits fest auf eine Unterlage (Quarzglastrager bzw. Ampullenwand) aufgewachsen sind, wenn sie noch superparamagnetisches Verhalten zeigen.

Description: 1. Einleitung 2. Züchtungsmethode 2.1. Kristallzüchtung im geschlossenen System 3. Thermodynamische Abschätzung der Versuchsbedingungen 4. Apparative Voraussetzungen 4.1. Transportofen 4.2. Temperaturmessung und -kontrol1e 4.3. Elektromagnet 5. Durchführung der Experimente 5.1. Apparative Voraussetzungen für die Untersuchung der Ausgangs- und Endsubstanzen 5.1.1. Goniometrische Vermessungen 5.1.2. Röntgenographische Untersuchungen 5.1.3. Mikroskopische Untersuchungen 6. Verwendete Substanzen 6.1. Magnetit 6.1.1. Vorbehandlung des Magnetits 6.2. Hämatit 6.2.1. Vorbehandlung des Hämatits 6.3. Magnetische Untersuchung beider Ausgangssubstanzen 7. Ergebnisse bei der Einkristallzüchtung von Magnetit und Hämatit im Magnetfeld 7.1. Wachstumsformen 7.2. Orientierung 8. Kristallographische und magnetische Eigenschaften von Magnetit und Hämatit 8.1. Kristallographische Struktur des Magnetits 8.2 . Kristallographische Struktur des Hämatits 8.3 . Magnetokristalline Anisotropie 8.3.1. Temperaturabhängigkeit der Kristallanisotropie 8.4. Übersicht über die wichtigsten strukturellen und magnetischen Eigenschaften von Magnetit und Hämatit 9. Magnetische Struktur und Eigenschaften kleiner Teilchen 9.1. Magnetisierungsvorgang 9.2. Anisotropie 9.3. Superparamagnetismus 9.3.1. Magnetisierungsvorgang in Superparamagnetika 10. Deutung der Ergebnisse 10.1. Abschätzung kritischer Teilchengrößen 10.1.1. Allgemeines zur kritischen Teilchengröße Berechnung kritischer Teilchengrößen von Magnetit Kritische Teilchengröße von Hämatit Berechnung der kritischen Teilchengröße von Hämatit Abschätzung und Vergleich der magnetischen und thermischen Energie Bildanhang Literaturverzeichnis

Description: Teleseismic receiver functions have been calculated from data of a temporary seismological network of broad-band three-component stations to investigate the lithospheric and asthenospheric structure across the Late Caledonian Iapetus Suture Zone (ISZ) in southern Ireland. The stations were deployed during the Irish Seismological Lithospheric Experiment (ISLE 2002/3) and straddle the Killarney-Mallow Fault Zone, a remnant of the Variscan orogeny, and the ISZ, the inferred boundary between the Laurentia and Eastern Avalonia plates fused together during the Caledonian orogeny. Receiver functions from the western part of the network were projected onto the N–S VARNET 1996 seismic refraction profile, extending from the Old Head of Kinsale to Galway Bay in SW Ireland. Laterally continuous P to S conversions from the Moho at delay times of about 3.8–4.1 s are clearly observed, and correspond to Moho depths of about 29–32 km. The Moho has a transitional character to the south of the ISZ. Synthetic receiver functions, calculated from a 2-D velocity model of the previous VARNET experiment, show Moho conversions and multiple crustal phases compatible to those observed in the ISLE data. Furthermore, P to S conversions from the 660 km discontinuity (66–68 s delay time) are well determined at the stations. In comparison, the conversion from the 410 km discontinuity at about 43–45 s delay time is considerably weaker. Delay times of stacked receiver functions from the mantle transition zone are in agreement with the standard iasp91 earth model and thus no structural changes are observed across the ISZ at this depth interval.

Description: We obtain well-resolved 1-D models of the shear wave velocity vs under the Eifel region, Central Europe, from teleseismic surface waves. Using 41 temporary and permanent broad-band stations and 30 events we determine regional and local dispersion curves from Rayleigh and Love waves. The inverted regional vs models show the asthenosphere at about 70 km depth. A subset of 35 stations, which are located close to the Quaternary Eifel volcanic fields, provide data with high resolution for a local Eifel vs model. Both, Rayleigh and Love wave models indicate an upper boundary of a low-velocity zone (LVZ) at just 45–50 km depth. The maximum vs perturbation is about −3 per cent. We interpret this shallow LVZ as the top of the Eifel plume. Receiver functions reveal a similar depth for this seismic discontinuity, but body wave tomography could not clearly resolve the top of the Eifel plume due to smearing along subvertical ray paths. Thus our results provide an important piece of information about the small Eifel upper mantle plume.

Description: The Urals Seismic Experiment and Integrated Studies (URSEIS), Mikhailovsky, and Europrobe's Seismic Reflection Profiling in the Urals (ESRU) reflection seismic profiles provide constraints for the construction of balanced and restored geological cross sections across the southern and middle Urals foreland. The profiles image the transition from the undeformed foreland basin to the frontal structure of the foreland thrust and fold belt, the location of the basal detachment, and the location of the ramp down into the middle or lower crust. In the URSEIS and ESRU profiles, the transition into the undeformed foreland basin is imaged as an emergent west-vergent thrust that deforms a westward thickening package of reflections related to synorogenic sediments, whereas in the Mikhailovsky profile, it is a buried system of imbricate thrusts. In all three data sets, the western flank of the foreland thrust and fold belt is imaged in the seismic data as an imbricate thrust system developed above a basal detachment located in either the upper part of the Neoproterozoic basement sediments or the lower part of the Paleozoic continental margin sediments. Truncation of reflections related to the undeformed sediments in the footwall to the imbricate thrust system mark the location of the ramp down of the basal detachment into the middle or lower crust beneath the basement-cored anticlines along the eastern flank of the thrust belt. The URSEIS and ESRU profiles image the basement-cored anticlines as predominantly east dipping reflections that extend into the middle and lower crust. Rocks in these anticlines record at least one phase of pre-Uralide deformation and, at least in part, the reflectivity is due to this deformation event. Balanced and restored cross sections constructed along the three profiles indicate that the minimum shortening is about 20–25 km.

Description: Die Ergebnisse der Untersuchungen im Rahmen des DFG-Projekts erweitern und verbessern die bisherige Kenntnis über den rezenten Spannungszustand von Mitteleuropa. Die Meßergebnisse vom Raum Sachsen-Thüringen als Teil des Grenzgebietes Böhmisches Massiv gegen das südwestliche Vorland beruhen auf oberflächennahen in-situ-Messungen. Obwohl sie nur die Spannungsverteilung der obersten Kruste wiederspiegeln, ergeben sie ein interpretierbares Bild. Trotz ermittelter Variabilität der Spannungsrichtungen und - Intensitäten ist eine Geologie-relevante Felderung in Gebiete mit relativ homogenen Spannungsrichtungen erkennbar. In-situ-Spannungsmessungen sind offenbar trotz aller Einschränkungen, die den Autoren bewußt sind, geeignet, das unterschiedliche rezente Verhalten geologischer Strukturen zu ermitteln. Nachweisbar ist der Einfluß rezent aktiver regionaler Störungszonen auf das Spannungsfeld: Gestützt wird die Aussagefähigkeit der Meßdaten durch zahlreiche Ergebnisse anderer Autoren (und Methoden), mit denen sie in der Regel übereinstimmen.

Description: In this report, we will present the complete derivation of analytical expressions of the EM coupling torque in dependence on the parameters of the fields contributing to it. For this, we choose a special set of spherically harmonic (SH) base functions and present all major steps of the derivation. Our report will be (i) closer to a lecture note than to a scientific paper and should give all readers the possibility to follow the derivations with the related details in the appendix, and can be (ii) used as a formulary for scientists working on this special field of investigation.

Description: [1] Using a high-quality broadband seismic data set of precursors to the phase SS, we investigate the structure of upper mantle discontinuities beneath the central Pacific including the Hawaiian hot spot. We image structure by stacking over 4000 records into geographic bins, retaining periods down to 5 s. We consider the effects of correcting for four separate tomographic models of mantle heterogeneity, excluding data at distances containing phases that potentially interfere with precursors. We find evidence for peak-to-peak topography of 15–20 km on the 670-km discontinuity and 7–28 km of topography on the 400-km discontinuity. Weak reflections are detected from discontinuities near 220- and 520-km depth. The average transition zone thickness beneath our region is approximately 242 ± 3 km, very similar to previous estimates of the global average. Lateral transition zone thinning and thickening weakly correlate with reduced and increased transition zone shear velocity, respectively, consistent with a thermal origin to topographical variations on the discontinuities within our study region. The transition zone beneath Hawaii and to the east of the Line Island Chain is thinned by up to 20 km in a province spanning nearly 1000 km, suggesting an excess mantle temperature of ∼200 K. In the oldest crustal regions of our study area (〉100 Ma), the 400-km discontinuity is relatively shallow, and the transition zone is relatively thick (250–255 km); a possible explanation for this pattern includes small-scale convection in the upper mantle bringing colder material into the transition zone.

Description: Field in-situ sinter growth studies have been carried out in five geochemically very different Icelandic geothermal areas with the aim to quantify the effects of water chemistry, (e.g. silica content (250 to 695 p.p.m. SiO(2)), salinity (meteoric to seawater), pH (7.5 to 10)), temperature (42-96 degrees C) and microbial abundance (prevalence, density) on the growth rates, textures and structures of sinters forming within and around geothermal waters. At each location, sinter growth was monitored over time periods between 30 min and 25 months using glass slides that acted as precipitation substrates from which sinter growth rates were derived. In geothermal areas like Svartsengi and Reykjanes, subaqueous sinters developed rapidly with growth rates of 10 and 304 kg year(-1) m(-2), respectively, and this was attributed primarily to the near neutral pH, high salinity and medium to high silica content within these geothermal waters. The porous and homogeneous precipitates that formed at these sites were dominated by aggregates of amorphous silica and they contained few if any microorganisms. At Hveragerdi and Geysir, the geothermal waters were characterized by slightly alkaline pH, low salinity and moderate silica contents, resulting in substantially lower rates of sinter growth (0.2-1.4 kg year(-1) m(-2)). At these sites sinter formation was restricted to the vicinity of the air-water interface (AWI) where evaporation and condensation processes predominated, with sinter textures being governed by the formation of dense and heterogeneous crusts with well-defined spicules and silica terraces. In contrast, the subaqueous sinters at these sites were characterized by extensive biofilms, which, with time, became fully silicified and thus well preserved within the sinter edifices. Finally, at Krafla, the geothermal waters exhibited high sinter growth rates (19.5 kg year(-1) m(-2)) despite being considerably undersaturated with respect to amorphous silica. However, the bulk of the sinter textures and structure were made up of thick silicified biofilms and this indicated that silica precipitation, i.e. sinter growth, was aided by the surfaces provided by the thick biofilms. These results further suggest that the interplay between purely abiotic processes and the ubiquitous presence of mesophilic and thermophilic microorganisms in modern silica rich terrestrial hydrothermal settings provides an excellent analogue for processes in Earth's and possibly Mars's ancient past.

Description: In der vorliegenden Arbeit werden der Einfluss seismischer Anisotropie auf wahre oder scheinbar auftretende tensile Quellanteile untersucht und Erdbebenmechanismen unter Berücksichtigung seismischer Anisotropie bestimmt. Es wird gezeigt, dass der Momententensor und die Abstrahlmuster eines Scherbruches im anisotropen Medium denen eines tensilen Bruches im isotropen Medium ähneln können. Umgekehrt treten Ähnlichkeiten tensiler Beben in anisotropen Gesteinen mit Scherbrüchen in isotropen Medien auf. Damit existieren Mehrdeutigkeiten beobachteter tensiler Quellanteile. Die Effekte von Anisotropie hängen von der Orientierung des Bruches und vom Grad der Anisotropie ab. Außerdem beeinflusst Anisotropie das Moment eines Bebens. [...] Mit dieser Arbeit werden erstmals zeitliche und räumliche Veränderungen tensiler Quellanteile und Spannungszustände im Vogtland für Erdbeben im Jahr 2000 beob- achtet. Diese haben auch dann Bestand, wenn seismische Anisotropie berücksichtigt wird. Sie können durch Fluide erklärt werden, die in die Bruchflächen eindringen.

Description: Results from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as welt as chain character and length. The analysed crystals showed a narrow size range (similar to 14-67 nm) with an average diameter of 46 +/- 6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range.

Description: Aus Messungen mit zwei verschiedenen Reversionspendelgeraten wird für den Doppelpfeiler SO im Pendelsaal des ehemaligen Geodätischen Institute Potsdam (seit 1969 Teil des Zentralinstituts Physik der Erde) der Schwerewert g = (981,260 1 ± 0,000 3) cm·s-2 abgeleitet. Dieser Wert entspricht einer Abweichung von -13,9 mGal gegenüber dem aus den Messungen von KÜHNEN und FURТWÄNGLER (1898 - 1904) abgeleiteten Bezugswert des Potsdamer Schweresystems. Die vorliegende Arbeit enthält neben grundsätzlichen Darstellungen zur Theorie des Reversionspendelverfahrens nähere Angaben zu den benutzten Geraten, den Meßergebnissen und der Ableitung des Schwerewertes. Sie wird ergänzt durch einen umfangreichen Überblick über die seit KÜHNЕN und FURТWÄNGLER (1898-1904) absoluten Schweremessungen und einen Vergleich dieser Arbeiten mit dem hier vorgelegten Ergebnis der neuen Potsdamer Reversionspendelmessungen.

Description: Tectonics of the eastern Mediterranean are strongly influenced by subduction of oceanic lithosphere with slab pull as a prominent driving force. The current distribution of remnants of oceanic lithosphere and the properties of African mantle lithosphere beneath the eastern Mediterranean basin have been a matter of debate. Previous studies variously found continental as well as oceanic lithosphere in this region. A set of 1-D S-wave velocity models is determined in order to characterize the mantle lithosphere in the area between Crete and the Middle East. For seven paths starting from Cyprus and running to Crete, to Anatolia as well as to the Middle East, broad-band average phase velocity curves of the fundamental Rayleigh mode are obtained in the frequency range of about 3 mHz to 90 mHz by a two-station method. In addition, an east–west oriented path crossing southern Anatolia and a path running parallel to the Dead Sea Fault Zone are considered. Phase velocity curves are inverted for path average 1-D S-wave velocity models. Resolution is investigated with the Neighbourhood Algorithm. Comparing the resulting 1-D models, cold oceanic mantle lithosphere showing S-wave velocities above 4.6 km s− 1 can be distinguished from mantle lithosphere with low S-wave velocities. Oceanic lithosphere is found west of Cyprus beneath the Herodotus basin. As indicated by Benioff zones, it is subducting towards northwest in the southeastern Aegean and towards northeast beneath southwestern Anatolia. To the east of Cyprus the mantle lithosphere beneath the easternmost Mediterranean Sea shows low S-wave velocities. No indications for cold oceanic mantle lithosphere are found beneath the Levant basin. In the region of the Dead Sea Fault Zone and the Levant basin the lithosphere–asthenosphere boundary is located at shallow depths of about 60 km to 80 km. The DSFZ is situated in a region of thinned lithosphere underlain by an asthenosphere with anomalous low S-wave velocities. Low S-wave velocities beneath southern Anatolia extend down to at least 150 km depth as expected for a back arc setting. Inferred Moho depths vary for the different paths between 28 km and 41 km