ALBERT

Beschreibung: Plant-driven fungal weathering is a major pathway of soil formation, yet the precise mechanism by which mycorrhiza alter minerals is poorly understood. Here we report the first direct in situ observations of the effects of a soil fungus on the surface of a mineral over which it grew in a controlled experiment. An ectomycorrhizal fungus was grown in symbiosis with a tree seedling so that individual hyphae expanded across the surface of a biotite flake over a period of three months. Ultramicroscopic and spectroscopic analysis of the fungus-biotite interfaces revealed intimate fungal-mineral attachment, biomechanical forcing, altered interlayer spacings, substantial depletion of potassium (similar to 50 nm depth), oxidation of the biotite Fe(II), and the formation of vermiculite and clusters of Fe(III) oxides. Our study demonstrates the biomechanical-chemical alteration interplay at the fungus-biotite interface at the nanometer scale. Specifically, the weathering process is initiated by physical distortion of the lattice structure of biotite within 1 mu m of the attached fungal hypha. Only subsequently does the distorted volume become chemically altered through dissolution and oxidation reactions that lead to mineral neoformation.

Beschreibung: We use traveltime data of local earthquakes and controlled sources observed by a large, temporary, amphibious seismic network to reveal the anatomy of the southcentral Chilean subduction zone (37–39°S) between the trench and the magmatic arc. At this location the giant 1960 earthquake (M = 9.5) nucleated and ruptured almost 1000 km of the subduction megathrust. For the three-dimensional tomographic inversion we used 17,148 P wave and 10,049 S wave arrival time readings from 439 local earthquakes and 94 shots. The resolution of the tomographic images was explored by analyzing the model resolution matrix and conducting extensive numerical tests. The downgoing lithosphere is delineated by high seismic P wave velocities. High v p/v s ratio in the subducting slab reflects hydrated oceanic crust and serpentinized uppermost oceanic mantle. The subducting oceanic crust can be traced down to a depth of 80 km, as indicated by a low velocity channel. The continental crust extends to approximately a 50-km depth near the intersection with the subducting plate. This suggests a wide contact zone between continental and oceanic crust of about 150 km, potentially supporting the development of large asperities. Eastward the crustal thickness decreases again to a minimum of about a 30-km depth. Relatively low v p/v s at the base of the forearc does not support a large-scale serpentinization of the mantle wedge. Offshore, low v p and high v p/v s reflect young, fluid-saturated sediments of forearc basins and the accretionary prism.

Beschreibung: We investigate depth variations of the 410 and 520 km-discontinuities beneath Asia and the Pacific which serve as examples for a continental and an oceanic region, respectively. The depths are derived from travel-time differences between the PP-phase and its precursors that are reflected at the discontinuities. After accounting for differences in average crustal thickness, we find that the depth of the ‘410’ is rather uniform but larger than expected beneath both regions with a value of approximately 418 km. Signals from the ‘520’ are slightly less pronounced. However, while the average depth of the ‘520’ beneath Asia is about 519 km, we obtain a value of about 531.5 km for the Pacific. Here, the depression of the discontinuities can be explained in view of thermal anomalies in relation to mantle plumes. For Asia, however, the observations seem to require a more complex pattern of thermal anomalies possibly complemented by variations in chemical composition.

Beschreibung: Providing quantitative microzonation results that can be taken into account in urban land-use plans is a challenging task that requires collaborative efforts between the seismological and engineering communities. In this study, starting from the results obtained by extensive geophysical and seismological investigations, we propose and apply an approach to the Gubbio basin (Italy) that can be easily implemented for cases of moderate-to-low ground motion and that takes into account not only simple 1D, but also more complicated 3D effects. With this method, the sites inside the basin are classified by their fundamental resonance frequencies, estimated from the horizontal-to-vertical spectral ratio applied to noise recordings (HVNSR). The correspondence between estimates of the fundamental frequency from this method and those derived from earthquake recordings was verified at several calibration sites. The amplification factors used to correct the response spectra are computed by the ratio between the response spectra at sites within the basin and the response spectra at a hard-rock site using data from two seismic transects. Empirical amplification functions are then assigned to the fundamental frequencies after applying an interpolation technique. The suitability of the estimated site-specific correction factors for response spectra was verified by computing synthetic response spectra for stations within the basin, starting from the synthetic recording at a nearby rock station, and comparing them with observed ones.

Beschreibung: The intention of this article is to present the definitions of different functionals of the Earth's gravity field and possibilities for their approximative calculation from a mathematical representation of the outer potential. [...] More or less, what is compiled here is well-known in physical geodesy but distributed over a lot of articles and books which are not cited here. In the first instance this text is targeted at non-geodesists and it should be "stand-alone readable".

Beschreibung: The Iquique Local Network (ILN), a temporal network of broadband and short period seismic stations has been operating in Northern Chile since 2009. The aim of this installation was to locally densify the permanent seismic installation of the Integrated Plate Boundary Observatory in Chile (IPOC), with the main goal to decrease the magnitude of detected earthquake, to improve the hypocentral location accuracy, to allow a more accurate investigation of seismic source parameters, and to analyse proposed seismogenic structures of the Northern Chile seismic gap. The network setup evolved with time, with different geometries at different installation phases, aiming to study different seismicity features. In the first phase, started in 2009 and operational since 2010 until autumn 2013, the network had a sparse configuration, targeting a broad region extending from 19.5° S in the North to approximately 21.3° S South of Iquique. In the following stage, operational until fall 2017, most broadband stations were rearranged into a small aperture seismic array (PicArray) close to the village of Pica, to monitor with array techniques the shallow seismicity at the plate interfacer, intermediate and deep focus seismicity. These data are freely available under the Creative Commons Attribution 4.0 International Licence (CC BY 4.0) at the GEOFON data centre under network code IQ.

Beschreibung: We use SAR interferometry to measure the strain accumulation along the left-lateral Haiyuan fault system (HFS), that marks the north-eastern boundary of the tibetan plateau. The last major earthquakes that occured along the HFS are the M~8 1920 Haiyuan earthquake (strike-slip mechanism) and the Ml=8-8.3 1927 Gulang earthquake that ruptured a thrust fault system. No large earthquake is reported on the central section of the HFS, the "Tianzhu seismic gap", since ~1000 years. We first analyze the complete ENVISAT SAR data archive along 4 descending and 2 ascending tracks for the 2003-2009 period and construct an InSAR-based mean Line-Of-Sight (LOS) velocity map around the HFS from the eastern end of the Qilian shan (102° E), to the west, to the Liupan shan (106° E), to the east. Data are processed using a small baseline chain type. For each track, all radar images are coregistrated to a single master and interferograms are produced using a local adaptative range filtering. Residual orbital and atmospheric delays are jointly inverted and corrected for each unwrapped interferogram. Atmospheric corrections are validated using the ERA40 global atmospheric model (ECMWF). The interferograms series on each track are then inverted to obtain the increments of LOS radar delays between acquisition dates, adapting the Lopez-Quiroz et al. 2009 time series analysis. The obtained LOS mean velocity maps show a dominant left-lateral motion across the fault with along-strike variations: some fault sections are locked at shallow depth while others are creeping and local vertical movements are observed (subsidence in the "Jingtai" pull-apart basin). For various fault slip rates imposed below 20 km (4-10 mm/yr), we model the shallow velocity by inverting the mean LOS velocity maps for both strike-slip and dip-slip motion on vertical, 5km x 2.5km discretized patches, using a least-square method with an appropriate degree of smoothing. The fault geometry follows the surface trace of the fault from SPOT images, with two main segments, on both sides of the Jingtai basin: one along the M~8 1920 rupture to the east and one along the creeping section to the west. For a far-field velocity of 6 mm/yr, the creeping rate is estimated to be up to 4 mm/yr on the western segment. We assess the influence of atmospheric noise on our velocity solution. Finally we compare the ENVISAT time series analysis with that obtained using the ERS dataset spanning the 1993- 1998 period to investigate for potential time variations of the strain accumulation across the Haiyuan fault.

Beschreibung: Waveforms of 50 teleseismic receiver functions and dispersion curves have been used to invert jointly for the 1D average crust and uppermost mantle seismic structure beneath GEOFON station ISP. The surface wave (Rayleigh and Love) dispersion curves were adopted from an earlier study and greatly help to stabilize the inversions by alleviating the deficiencies of inverting the receiver functions alone. The teleseismic receiver functions had a backazimuth distribution from which three stacks were created. All the stacks resulted in compatible inversions. Nine different influence factors ranging between 0.1 and 0.9 were employed and the influence factors around 0.5 were preferred for producing a reasonable seismic structure to represent the geology under station ISP. Three distinct crustal depth ranges are identified based on the inverted velocity-depth profile. The first corresponds to 0–5 km where the velocity-depth profile has a positive gradient with an increase from 2.5 km s−1 to 3.0 km s−1. The second depth range is 5–10 km and the velocity-depth profile shows a positive gradient between 3.0 km s−1 and 3.20 km s−1. A velocity jump from 3.20 km s−1 to 3.62 km s−1 tops the third depth range (10–20 km), which is characterized by a constant velocity. There is another velocity drop at 20 km depth from 3.62 km s−1 to 3.40 km s−1 and the low velocity therein is persistent down to 27.5 km. Below this depth range, the shear velocity increases until 40 km depth where the Moho discontinuity is estimated with Sn velocity of 4.4 km s−1. In general, seismic velocities under SW Anatolia are considerably slower than those of the Preliminary Reference Earth Model (PREM).

Beschreibung: We constrain structural features and shear-velocity structure of a low-velocity anomaly in the lower mantle beneath the Pacific (we term it the “Pacific Anomaly”) on the basis of forward travel time and waveform modeling of the observed direct S, Sdiff, ScS, SKS, and SKKS phases sampling a great arc across the anomaly from eastern Eurasia to southern South America. After correction for the effects of earthquake mislocation and the seismic heterogeneities outside the Pacific Anomaly, seismic observations suggest that the Pacific Anomaly along the great arc consists of at least two separated portions with a 740-km-wide gap between them. The western portion of the anomaly is about 1050 km wide, extends at least 740 km above the core-mantle boundary (CMB), and exhibits a trapezoidal shape with lateral dimensions increasing slightly with depth. The velocity structure of the western portion varies from −3.0% at the top (740 km above the CMB) to −3.5% at 100 km above the CMB and an average shear-velocity reduction of −5% in the bottom 100 km of the mantle. The eastern portion of the anomaly reaches at least 340 km above the CMB beneath the mid-Pacific with an 1800-km-wide base and has a uniform velocity reduction of −3%. Waveform modeling further suggests a very low velocity layer with a shear-velocity reduction of −10% located at the edge of the western portion of the anomaly. Combining the latest results from others, we present a general picture of structural and velocity structures of the Pacific Anomaly. The structural and velocity features suggest that the anomaly represents a cluster of metastable thermo-chemical piles.

Beschreibung: The paper consists of two main elements: (1) the creation of a harmonized seismicity data file for the eastern Mediterranean area and the generation of a classical timeindependent PSHA, and (2) the extension of the earthquake model of the timeindependent approach to a newly developed time‐dependent PSHA and the comparison with the results of (1).

Beschreibung: We present new shear wave splitting data from local events in Costa Rica and Nicaragua recorded by the temporary (July 2004 to March 2006) 48-station TUCAN broadband seismic array. Observed fast polarization directions in the fore arc, arc, and back arc range from arc-parallel to arc-normal over very short distances (〈5 km when plotted at raypath midpoints) making the direct interpretation of individual splitting measurements in terms of flow tenuous, even when considering variations in the relationship between lattice-preferred orientation and deformation (e.g., B-type dislocation creep in olivine). Therefore, we tomographically invert the splitting measurements to find a three-dimensional model of crystallographic orientation in the wedge. We assume the elastic constants of olivine and orthopyroxene with hexagonal symmetry and use a damped, iterative least squares approach to account for the nonlinear behavior of splitting when considering three-dimensional ray propagation and distributions of anisotropy. The best fitting model contains roughly horizontal, arc-parallel olivine [100] axes in the mantle wedge down to at least 125 km beneath the back arc and arc, which we interpret to indicate along-arc flow in the mantle wedge. Pb and Nd isotopic ratios in arc lavas provide additional evidence for arc-parallel flow and also constrain the direction (northwest, from Costa Rica to Nicaragua) and minimum flow rate (63–190 mm/a). With only slightly oblique subduction at 85 mm/a of the relatively planar Cocos Plate, the most likely mechanism for driving along-arc transport is toroidal flow around the edge of the slab in southern Costa Rica, generated by greater slab rollback in Nicaragua. Two important implications of this arc-parallel flow are the progressive depletion of the mantle source for arc lavas from Costa Rica to Nicaragua and the possible need for significant decoupling between the wedge and downgoing plate.

Beschreibung: A temporary local seismic network was installed in the basin of Norcia (Italy) in January 2009 and operated until May 2009. Several recordings collected by the network are earthquakes of the 2009, Mw 6.3 L'Aquila seismic sequence. The seismic equipments consisted of fifteen Earth-Data Loggers (24 bit) connected to Mark L4-3D sensors (1Hz). The stations continuously recorded at a rate of 100 samples per second, and the timing was provided by a GPS link. This work was carried out in the framework of Project S4 “The Italian strong motion database”, funded within the DPC-INGV 2007–2009 Agreement, between the Italian Department of Civil Protection and the Istituto Nazionale di Geofisica e Vulcanologia. Waveform data are available from the GEOFON data centre, under network code 3H.

Beschreibung: Depth distributions of seismic velocities and their directional dependence (anisotropy) in the crust and mantle beneath cratons yield essential constraints on processes of their formation and evolution. Despite recent progress in mapping the lateral extent of cratonic roots around the globe, profiles of seismic velocities within them remain uncertain. In this study we employ a novel combination of waveform-analysis techniques and measure inter-station Rayleigh- and Love-wave phase velocities in broad period ranges that enable resolution from the upper crust to deep upper mantle. Sampling a selection of 10 Archean and Proterozoic locations, we derive new constraints on the isotropic and radially anisotropic seismic structure of Precambrian lithosphere. Shear-wave speed VS is consistently higher in the lithosphere of cratons than in the lithosphere of Proterozoic foldbelts. Because known effects of compositional variations in the lithosphere on VS are too small to account for the difference, this implies that temperature in cratonic lithosphere is consistently lower, in spite of sub-lithospheric mantle beneath continents being thermally heterogeneous, with some cratons underlain, as we observe, by a substantially hotter asthenosphere compared to others. Lithospheric geotherms being nearly conductive, this confirms that the stable, buoyant lithosphere beneath cratons must be substantially thicker than beneath younger continental blocks. An increase in VS between the Moho and a 100-150 km depth is consistently preferred by the data in this study and is present in seismic models of continents published previously. We argue that this is largely due to the transition from spinel peridotite to garnet peridotite, proposed previously to give rise to the “Hales discontinuity” within this depth interval. The depth and the width of the phase transformation depend on mantle composition; it is likely to occur deeper and over a broader depth interval beneath cratons than elsewhere because of the high Cr content in the depleted cratonic lithosphere, as evidenced by a number of xenolith studies. Seismic data available at present would be consistent with both a sharp and a gradual increase in VS in the upper lithosphere (a Hales discontinuity or a “Hales gradient”). The VS profile in the upper mantle lithosphere is not shaped by the temperature distribution only; this needs to be considered when relating seismic velocities to lithospheric temperatures. Radial anisotropy in the upper crust is observed repeatedly and indicates vertically oriented anisotropic fabric (VSH 〈 VSV); this may yield a clue on how cratons grew, lending support to the view that distributed crustal shortening with sub-vertical flow patterns occurred over large scales in hot ancient orogens. In the lower crust and upper lithospheric mantle, radial anisotropy consistently reveals horizontal fabric (VSH 〉 VSV); the fabric can be interpreted as a record of (sub-)horizontal ductile flow in the lower crust and lithospheric mantle at the time of the formation and stabilisation of the cratons. We also find indications for radial anisotropy below 200 km depth, corroborating recent evidence for anisotropy in the asthenosphere beneath cratons due to current and recent asthenospheric flow.

Beschreibung: On 8 January 2006 at 11:34 (GMT) a strong (Mw 6.7) subcrustal earthquake occurred near Kythira island in southern Greece, causing damage to the surrounding area while the shock was also felt in most of the eastern Mediterranean. The event and its aftershocks were recorded by a regional network of 31 stations equipped with three-component broad-band seismometers that cover most parts of the Greek region. Initial locations of the earthquake sequence showed a diffuse pattern, therefore catalog and cross-correlation differential travel times were input to a shrinking grid-search relocation algorithm in order to obtain accurate relative locations. After this relocation most aftershocks form a tight cluster around the mainshock at depths between 44 and 53 km. Subsequently, waveforms from 12 stations giving the best possible azimuthal coverage around the Kythira event were inverted in order to investigate its source process. A parallel, non-negative least-squares inversion technique utilizing multiple time windows was used to derive the spatiotemporal slip distribution. The fault surface was parameterized by subfaults of 3 km × 3 km size covering a length and down-dip width of 91 and 100 km, respectively. Inversion results indicate that the fault plane is probably the one dipping towards SE. The slip distribution model showed that there are two areas of large slip (∼60 cm), the largest extending between 38 and 80 km depth and a smaller one at depths 65–82 km. The moment rate function consists of a large initial peak with a duration of about 11 s followed by a number of smaller peaks, probably due to coseismic slip on some of the subfaults. Furthermore, the hypocenters of the relocated aftershocks coincide with the areas of minimum slip (〈10 cm) while the hypocenter of the mainshock is located near the edge of the larger slip patch. Sensitivity and resolution tests confirmed the adequacy of the inversion parameters used and the stability of the solution. The Kythira earthquake was probably caused by the contortion of the downgoing African slab that results in the development of along-strike compression forces in the Kythira strait.

Beschreibung: The passive margin of the South Atlantic shows typical features of a rifted volcanic continental margin, encompassing seaward dipping reflectors, continental flood basalts and high-velocity/density lower crust at the continent–ocean transition, probably emplaced during initial seafloor spreading in the Early Cretaceous. The Springbok profile offshore western South Africa is a combined transect of reflection and refraction seismic data. This paper addresses the analysis of the seismic velocity structure in combination with gravity modelling and isostatic modelling to unravel the crustal structure of the passive continental margin from different perspectives. The velocity modelling revealed a segmentation of the margin into three distinct parts of continental, transitional and oceanic crust. As observed at many volcanic margins, the lower crust is characterised by a zone of high velocities with up to 7.4 km/s. The conjunction with gravity modelling affirms the existence of this body and at the same time substantiated its high densities, found to be 3100 kg/m3. Both approaches identified the body to have a thickness of about 10 km. Yet, the gravity modelling predicted the transition between the high-density body towards less dense material farther west than initially anticipated from velocity modelling and confirmed this density gradient to be a prerequisite to reproduce the observed gravity signal. Finally, isostatic modelling was applied to predict average crustal densities if the margin was isostatically balanced. The results imply isostatic equilibrium over large parts of the profile, smaller deviations are supposed to be compensated regionally. The calculated load distribution along the profile implies that all pressures are hydrostatic beneath a depth of 45 km.

Beschreibung: This paper presents new insights into the South American subduction zone from reprocessed seismic images. We applied a 3D Kirchhoff prestack depth migration scheme to data sets containing different narrow frequency ranges in order to extract additional details from seismic reflection images. This approach accounts for the effects of scattering on the seismic image, especially for structures below a heterogeneous overburden. The reflection image in such environments will differ significantly when focusing on different frequency ranges due to the frequency dependence of scattering that is likely to be present. The narrow frequency range images uncover reflectors in one frequency range that are masked in another range. Furthermore, the images enable for instance the characterization of the medium in terms of scatterer concentration and thus improve the structural interpretation. The analysis of these images might help to distinguish between small-scale structures in the high-frequency band and large-scale structures in the low-frequency band. We call this imaging approach Reflection Image Spectroscopy (RIS). We applied the RIS approach to the ANCORP'96 data set, an onshore deep seismic reflection profile across the South American Central Andes. The narrow frequency range images revealed additional details that we interpret as features directly linked to fluid migration processes in the subduction zone. Furthermore, structural details of the oceanic crust and the overlying mantle and crust are revealed. From the narrow-frequency range images we interpret that the top of the so called Nazca reflector at 70 km depth marks the upper limit of the hydrated mantle wedge, whereas the bottom of the reflector represents the top of the subducted oceanic crust. The compilation of our results with local earthquake data confirms this interpretation. Similar features observed in another deep seismic profile (PRECORP'95) support this interpretation, too. Furthermore, the RIS images show a highly reflective heterogeneous zone between the Nazca reflector at 70 km depth and a prominent mid-crustal Bright Spot (Quebrada Blanca Bright Spot) at about 30 km depth. We associate this zone with a complex network of ascending fluids or partial melts, initiated by ascending fluids released from the subducted oceanic plate. This observation links the Quebrada Bright Spot directly to the dehydrating oceanic plate.

Beschreibung: In this study we present the new tomographic code ANITA which provides 3-D anisotropic P and isotropic S velocity distribution based on P and S traveltimes from local seismicity. For the P anisotropic model, we determine four parameters for each parameterization cell. This represents an orthorhombic anisotropy with one predefined direction oriented vertically. Three of the parameters describe slowness variations along three horizontal orientations with azimuths of 0°, 60°, and 120°, and one is a perturbation along the vertical axis. The nonlinear iterative inversion procedure is similar to that used in the LOTOS code. We have implemented this algorithm for the updated data set of central Java, part of which was previously used for the isotropic inversion. It was obtained that the crustal and uppermost mantle velocity structure beneath central Java is strongly anisotropic with 7–10% of maximal difference between slow and fast velocity in different directions. In the forearc (area between southern coast and volcanoes), the structure of both isotropic and anisotropic structure is strongly heterogeneous. Variety of anisotropy orientations and highly contrasted velocity patterns can be explained by a complex block structure of the crust. Beneath volcanoes we observe faster velocities in vertical direction, which is probably an indicator for vertically oriented structures (channels, dykes). In the crust beneath the middle part of central Java, north to Merapi and Lawu volcanoes, we observe a large and very intense anomaly with a velocity decrease of up to 30% and 35% for P and S models, respectively. Inside this anomaly E-W orientation of fast velocity takes place, probably caused by regional extension stress regime. In a vertical section we observe faster horizontal velocities inside this anomaly that might be explained by layering of sediments and/or penetration of quasi-horizontal lenses with molten magma. In the mantle, trench parallel anisotropy is observed throughout the study area. Such anisotropy in the slab entrained corner flow may be due to presence of B-type olivine having predominant axis parallel to the shear direction, which appears in conditions of high water or/and melting content.

Beschreibung: Hydrological model evaluation and identification essentially involves extracting and processing information from model time series. However, the type of information extracted by statistical measures has only very limited meaning because it does not relate to the hydrological context of the data. To overcome this inadequacy we exploit the diagnostic evaluation concept of Signature Indices, in which model performance is measured using theoretically relevant characteristics of system behaviour. In our study, a Self-Organizing Map (SOM) is used to process the Signatures extracted from Monte-Carlo simulations generated by the distributed conceptual watershed model NASIM. The SOM creates a hydrologically interpretable mapping of overall model behaviour, which immediately reveals deficits and trade-offs in the ability of the model to represent the different functional behaviours of the watershed. Further, it facilitates interpretation of the hydrological functions of the model parameters and provides preliminary information regarding their sensitivities. Most notably, we use this mapping to identify the set of model realizations (among the Monte-Carlo data) that most closely approximate the observed discharge time series in terms of the hydrologically relevant characteristics, and to confine the parameter space accordingly. Our results suggest that Signature Index based SOMs could potentially serve as tools for decision makers inasmuch as model realizations with specific Signature properties can be selected according to the purpose of the model application. Moreover, given that the approach helps to represent and analyze multi-dimensional distributions, it could be used to form the basis of an optimization framework that uses SOMs to characterize the model performance response surface. As such it provides a powerful and useful way to conduct model identification and model uncertainty analyses.

Beschreibung: The initial steps of silica polymerization and silica nanoparticle formation have been studied in-situ and in real-time. The experiments were carried out in near neutral pH (7-8) solutions with initial silica concentrations of 640 and 1600 ppm ([SiO(2)]) and ionic strengths (IS) of 0.02, 0.05, 0.11 and 0.22 M. The polymerization reactions were induced by neutralizing a high pH silica solution (from pH 12 to 7) and monitored by the time-dependent depletion in monosilicic acid concentration over time. The accompanied nucleation and growth of silica nanoparticles (i.e., change in particle size over time) was followed in-situ using time-resolved synchrotron-based Small Angle X-ray Scattering (SAXS) and conventional Dynamic Light Scattering (DLS) combined with scanning and (cryo)-transmission electron microscopy (SEM/cryo-TEM). The critical nucleus diameter was quantified (1.4-2 nm) and results from SAXS and DLS showed that over 3 It the particle diameter increased to a final size of similar to 8 nm. SEM and TEM photomicrographs verified the SAXS and DLS data and confirmed the spherical and hydrous structure of the forming silica nanoparticles. Furthermore, fractal analysis (i.e., fractal dimension, D(m) similar to 2.2) indicated that the formed particles consisted of open, polymeric, low-density structures. For the nucleation and growth of silica nanoparticles a 3-stage growth process is proposed: (1) homogeneous and instantaneous nucleation of silica nanoparticles, (2) 3-D, surface-controlled particle growth following 1st order reaction kinetics and (3) Ostwald ripening and particle aggregation. (C) 2009 Elsevier Ltd. All rights reserved.

Beschreibung: The nucleation and crystallization of Al and Fe phosphate phases directly from aqueous solutions were investigated experimentally in batch reactors at 50 to 200 degrees C and pH 1.6. The mineralogy, elemental composition, and morphology of the formed solids were characterized by X-ray diffraction, spectroscopy, and high-resolution microscopic techniques. The corresponding dissolved aqueous Al, Fe,and P concentrations were analyzed by spectroscopic and chromatographic techniques. In all experiments Al and Fe phosphate phases readily precipitate from supersaturated solutions. Precipitation is initiated by the nucleation and growth of amorphous Al or Fe phosphate precursors. These crystallize at T = 100 degrees C to either variscite and metavariscite or strengite and phosphosiderite, respectively. At T 〉= 150 degrees C, these Al and Fe amorphous phases recrystallize to either berlinite or ferric giniite, respectively. The composition of the aqueous solution in all cases evolves rapidly to near saturation with respect to variscite and strengite. These observations suggest that Al and Fe phosphates may be critical to limiting aqueous phosphate availability in many natural environments.

Beschreibung: First long-period magnetotelluric investigations were conducted in early 2008 in northwestern Costa Rica, along a profile that extends from the coast of the Pacific Ocean, traverses the volcanic arc and ends currently at the Nicaraguan border. The aim of this study is to gain insight into the electrical resistivity structure and thus fluid distribution at the continental margin where the Cocos plate subducts beneath the Caribbean plate. Preliminary two-dimensional models map the only moderately resistive mafic/ultramafic complexes of the Nicoya Peninsula (resistivity of a few hundred Ωm), the conductive forearc and the backarc basins (several Ωm). Beneath the backarc basin the data image a poor conductor in the basement with a clear termination in the south, which may tentatively be interpreted as the Santa Elena Suture. The volcanic arc shows no pronounced anomaly at depth, but a moderate conductor underlies the backarc with a possible connection to the upper mantle. A conductor at deep-crustal levels in the forearc may reflect fluid release from the downgoing slab.

Beschreibung: Medium resolution SAR satellite data have been widely used for water and flood mapping in recent years. Since 2007 high resolution radar data with up to 1 m pixel spacing of the TerraSAR-X satellite are operationally available. The improved ground resolution of the system offers enormous potential for water detection. However, image analysis gets more challenging due to the large amount of image objects that are visible in the data. Water body detection methods are reviewed with regard to their applicability for TerraSAR-X data. Flood detection approaches for rapid disaster mapping are presented in this paper.

Beschreibung: The North Anatolian Fault Zone (NAFZ) below the Sea of Marmara forms a “seismic gap” where a major earthquake is expected to occur in the near future. This segment of the fault lies between the 1912 Ganos and 1999 İzmit ruptures and is the only NAFZ segment that has not ruptured since 1766. To monitor the microseismic activity at the main fault branch offshore of Istanbul below the Çınarcık Basin, a permanent seismic array (PIRES) was installed on the two outermost Prince Islands, Yassiada and Sivriada, at a few kilometers distance to the fault. In addition, a temporary network of ocean bottom seismometers was deployed throughout the Çınarcık Basin. Slowness vectors are determined combining waveform cross correlation and P wave polarization. We jointly invert azimuth and traveltime observations for hypocenter determination and apply a bootstrap resampling technique to quantify the location precision. We observe seismicity rates of 20 events per month for M 〈 2.5 along the basin. The spatial distribution of hypocenters suggests that the two major fault branches bounding the depocenter below the Çınarcık Basin merge to one single master fault below ∼17 km depth. On the basis of a cross-correlation technique we group closely spaced earthquakes and determine composite focal mechanisms implementing recordings of surrounding permanent land stations. Fault plane solutions have a predominant right-lateral strike-slip mechanism, indicating that normal faulting along this part of the NAFZ plays a minor role. Toward the west we observe increasing components of thrust faulting. This supports the model of NW trending, dextral strike-slip motion along the northern and main branch of the NAFZ below the eastern Sea of Marmara.