ALBERT

Description: 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.

Description: Leichtschamotte, Stückschamotte, Mahlschamotte. Produkte, für die die Pohnholzer Rohstoffgesellschaft einen Qualitätsbegriff darstellt. Am 14. Mai hatten die Mitglieder des Vereins der Freunde und Förderer des GFZ (FFGFZ) die Gelegenheit, die Produktion vor Ort zu besichtigen. Teilnehmer der Exkursion waren dieses Mal vor allem Studenten. Der zweite Vorsitzende und Geschäftsführer des Fördervereins, Oliver Bens, zeigte sich erfreut über das Interesse des wissenschaftlichen Nachwuchses an den Aktivitäten des Vereins. „Es ist schön, dass sich zunehmend auch jüngere Leute an unseren Aktivitäten beteiligen, denn die Studierenden sind die Zukunft der Geowissenschaften."

Description: 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.

Description: Wie lassen sich Informationen auf digitalen Karten verständlich und übersichtlich darstellen? Ein neuer Kurstag zum Thema „Geoinformationssysteme/GPS“ des Schülerlabors „GeoLab“ soll diese Frage beantworten. Zum ersten Labortag besuchten Schüler der 11. Jahrgangsstufe des Ratsgymnasiums Rheda-Wiedenbrück am 26. August das GeoLab. Hier hatten die potentiellen Nachwuchs-Geowissenschaftler unter der Anleitung des GFZ-GIS-Experten Matthias Schröder aus dem CeGIT die Möglichkeit, den Umgang mit Geoinformationssystemen und GPS-Geräten zu üben. Andreas Küppers, einer der Initiatoren des GeoLab: „Das GFZ wächst ständig und bietet hervorragende Entwicklungsmöglichkeiten für den wissenschaftlichen Nachwuchs. Daher ermöglichen wir interessierten Schülern einen Einblick in die spannende Arbeit unserer Wissenschaftler. Bestimmt können wir vielen damit die Berufswahl erleichtern.“

Description: Der bisherige Entwurf des CCS-Gesetzes löste eine intensive politische Diskussion über die Nutzung des Untergrundes für CO2-Speicherung und Geothermie aus. Das GFZ betreibt als weltweit einzige Forschungseinrichtung zwei entsprechende Pilotstandorte. Die GeoForschungsZeitung befragte die Projektleiter zu diesem Thema.

Description: 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.

Description: 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.

Description: 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".

Description: 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.

Description: 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.

Description: „Die Produktivität liegt jetzt bei einer Absenkung des Wasserspiegels von 500 Metern bei 65 bis 75 Kubikmeter pro Stunde, vorher hatten wir weniger als fünf“, freute sich Sektionsleiter Ernst Huenges nach der Bohrlochreinigung in Groß Schönebeck. In der Nacht vom 22. zum 23. April wurde das Bohrloch mit Säure gereinigt, um die Durchlässigkeit des Gesteins weiter zu erhöhen und damit für den folgenden Langzeittest vorzubereiten.

Description: Vier mal 4,8 Kilometer mussten 17 Mitarbeiter des GFZ auf dem ersten Potsdamer Firmenlauf bewältigen. Auf sportliche Weise konnten die Kolleginnen und Kollegen ihre Ausdauer mit 400 Läufern am 24. Juni im Buga-Park messen. Mit kreativen Trickots und sportlichen Spitzenleistungen hat sich das GFZ mit einem zweiten Platz bei den Herren und einem fünften Platz bei den Frauen teuer verkauft.

Description: Um Punkt neun Uhr beginnt der Tag für Leila Tarrien im Besprechungsraum der Sektion 3.3. Die gebürtige Französin ist Erasmus-Studentin an der FU in Berlin und bearbeitet derzeit am GFZ ein eigenes kleines Forschungsprojekt. Jährlich absolvieren fünf Studenten der Geologie und Mineralogie aus ganz Deutschland ein außeruniversitäres Praktikum am GFZ. Sie sollen Einblicke in die Forschung erhalten und ein möglichst breites Spektrum an wissenschaftlichen Methoden erlernen. Am 16. Februar ging das Praktikantenprogramm der Sektion 3.3 "Chemie und Physik der Geomaterialien" von Prof. Dr. Wilhelm Heinrich in die siebte Runde.

Description: „Wunderkammer Wissenschaft“ heisst die neue Wanderausstellung der Helmholtz- Gemeinschaft, die anlässlich der HG-Jahrestagung im Deutschen Technikmuseum eröffnet wurde. Die größte deutsche Forschungsorganisation lädt die Besucherinnen und Besucher dazu ein, in die faszinierende Welt der Wissenschaft einzutauchen. Noch bis zum 1. November ist die Ausstellung dort zu sehen.

Description: Jedes Jahr werden die Anden oder das Himalaya ein paar Millimeter durch die Kräfte der Plattenverschiebungen in die Höhe geschoben, wo Wind und Wetter sie wieder klein mahlen. Es ist nicht überraschend, dass diese Hochgebirge die Regionen mit dem schnellsten Abtrag von Boden auf diesem Planeten sind. Auch die Gebirge auf der tropischen Insel Sri Lanka haben ein steiles Relief. Heute stoßen dort jedoch keine Platten mehr zusammen. Ist die Erosion deshalb viel langsamer? Als der neu an das GFZ berufene Geochemiker Friedhelm von Blanckenburg mit seinen Kollegen zum tropischen Eiland reiste, fand er alle Spuren starker Erosion vor. Die Monsunregen schwemmen die fruchtbaren Böden von den Plantagen in die Flüsse. Diese, mit Sedimenten überladen, drohen schließlich die Stauseen zur Stromerzeugung lahmzulegen. Doch woher wissen wir, ob diese schnelle Erosion überhaupt erst begonnen hat, als vor rund 300 Jahren die Menschen die Tropenwälder der Insel fast vollständig abholzten und Tee, Gemüse und Getreide anbauten?

Description: 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).

Description: Übergewichtig? Vielleicht sollten Sie Ihre Waage mit auf einen Alpengipfel nehmen. Dort schlägt der Zeiger nämlich geringfügig weniger aus. Um zu klären, wo genau Sie am „leichtesten“ wären, begab sich Hartmut Pflug vom GFZ im September auf eine Reise über die Alpen. In Kooperation zwischen dem Bundesamt für Kartographie und Geodäsie (BKG), der Bundesanstalt für Geowissenschaften und Rohstoffe Hannover (BGR) und dem GFZ wurde eine fluggravimetrische Kampagne zu Schweremessungen durchgeführt, die „AlpinAero2008“. Pflug: „Zurzeit existiert für die deutschen Alpen und das Alpenvorland kein einheitlicher Datensatz von Schweremessungen. In Gebieten mit rauer Topographie und über großen Gewässern, wie dem Starnberger See und dem Bodensee, weist der Datensatz sogar größere Lücken auf. Diese sollte die herbstliche Überfliegung schließen.“

Description: Es ist geschafft: Die letzten Bojen des Tsunami-Frühwarnsystems GITEWS sind vor der Küste Indonesiens ausgesetzt. Am 10. April legte das Forschungsschiff FS SONNE mit den GFZ-Mitarbeitern um Projektleiter Tilo Schöne vom Hafen in Merak/Indonesien ab. Mit an Bord waren die letzten acht Bojen des Frühwarnsystems GITEWS und Ozeanbodeneinheiten des Alfred-Wegener-Instituts. Schöne: „Damit können wir jetzt einen Tsunami mit einer sehr hohen Verlässlichkeit erfassen.“

Description: Auf 3420 Metern Höhe fällt das Atmen schwer, besonders wenn man dabei auch noch hart arbeiten muss. Doch den kirgisischen Technikern schienen diese Umstände bei ihrer Arbeit nichts auszumachen. Umgeben von 7000 Meter hohen Berggipfeln des Tien Shan, versuchten sie mit Spitzhacken und Schaufeln den Aufbau einer Forschungsstation vorzubereiten. Der GFZ-Expeditionsleiter Uli Wetzel übernachtete fast drei Wochen im Zelt vor Ort. Zusammen mit dem Projektleiter des ZAIAG aus Bischkek, Alexey Dudashvili und 20 weiteren Expeditionsteilnehmern, bauten sie am Merzbacher See eine wissenschaftliche Forschungs- und Basisstation als Teil des „Global Change Observatoriums Zentralasien (GCO)“ auf. Hydrologische, meteorologische und glaziologische Daten soll die Gottfried Merzbacher-Station liefern, um für den Inylchek-Gletscher die Veränderung seiner Eismasse vor dem Hintergrund der Klimaänderungen zu erfassen. Wissenschaftler aus aller Welt sollen die Forschungsstation am zweitgrößten Hochgebirgsgletscher der Erde nutzen können.

Description: Projekte des International Continental Scientific Drilling Program (ICDP) erzeugen große Mengen an Daten, die schon zur Laufzeit der Projekte über die Informationssysteme des ICDP den Projektteilnehmern zur Verfügung gestellt werden. Nach Ende der Projekte und für Dritte sind die Daten jedoch meist unzugänglich. Daten, die Grundlage einer Veröffentlichung waren und weitere Daten aus wissenschaftlichen Bohrprojekten können seit einiger Zeit über die Scientific Drilling Database (SDDB) veröffentlicht werden. Dieser Vortrag beleuchtet die informationstechnischen Konzepte der SDDB und skizziert die geplante weitere Entwicklung der Plattform.

Description: 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.

Description: 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).

Description: 240 Tote, zehntausende Obdachlose: Das Hochwasser im Jahr 2000 im Mekong-Delta forderte viele Opfer. Grund genug für die Wissenschaftler Heiko Apel und Heiko Thoss, zusammen mit dem vietnamesischen Doktoranden Nguyen Nghia Hung, ein Hochwassermonitoring in der Region zu entwickeln. Seit dem Frühjahr 2007 testen sie dafür in Kooperation mit dem DLR im Projekt WISDOM neue Geräte. Apel: „Für uns ist das Mekong-Delta ein ideales Versuchsgebiet zur Entwicklung eines Hochwassermonitorings, da es hier durch den Monsun und Taifune aus dem Südchinesischen Meer jedes Jahr zu Überflutungen kommt.“

Description: Wie bringe ich eine 100 Tonnen schwere Bohranlage 250 Kilometer weit in die Tundra Sibiriens? Diese Frage zu beantworten war eine der größten logistischen Herausforderungen des Internationalen Bohrprogramms ICDP. Schiffe, Lastwagen und Schneeraupen transportierten die Bohranlage in Einzelteilen durch die arktische Wildnis. Weitere Güter sowie das wissenschaftliche und technische Personal wurden mit Helikoptern eingeflogen. Ziel war der See El´gygytgyn, was auf Tschuktschisch „der Weiße See“ bedeutet. Klimaforscher erhoffen sich hier weitreichende Erkenntnisse über die massive Abkühlung der Arktis am Ende des Tertiärs zu gewinnen. Jochen Kück und Martin Töpfer vom GFZ beteiligten sich an der Expedition, um Bohrlochmessungen vorzunehmen. Uli Harms, Geschäftsführer von ICDP: „Die Bohrungen in den Seeboden des El´gygytgyn waren aufgrund der schwierigen Logistik eine besondere Herausforderung. Allein der Transport der Bohranlage und des Camps hat über ein Jahr gedauert.“

Description: 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.

Description: Poster Session, Workshop und Vortragssession. Die diesjährige Veranstaltung fand unter dem Motto „Scientific Drilling“ statt. Die GeoForschungsZeitung fragte die Doktorandenvertreter Ursula Lengler und Phillipp Kuhn, was sich die Doktoranden von diesem Tag erhoffen.

Description: 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.

Description: Auf einer mit Russland vergleichbaren Fläche speichert sie ca. 90 Prozent des gesamten Süßwassers der Erdoberfläche: Die Antarktis, bedeckt mit der größten zusammenhängenden Eismasse der Erde. Würde das Eis vollständig abschmelzen, dann stiege der Meeresspiegel global im Mittel um 60 Meter an. Grund genug für GFZ-Wissenschaftler Ingo Sasgen, die Entwicklung des Eisschildes in der Antarktis zu untersuchen. Mithilfe des Satelliten GRACE bestimmt er die Schwankungen des Schwerefeldes über der Antarktis. Sasgen: „Langfristige Änderungen im Schwerefeld werden vor allem durch Eismassenänderungen in den Polarregionen dominiert. Das Problem ist, die damit verbundenen glazialisostatischen Hebungen und Senkungen im Schwerefeld von heutigen Eismassenverlagerungen zu unterscheiden."

Description: Am zweiten Weihnachtstag im Jahr 2004 um 02:10 Uhr meldete das automatische GFZ-Erdbebenmonitoring-System SeisComP ein Erdbeben. Der Meeresboden im Sundagraben riss auf und die seismischen Wellen wurden von den Stationen des seismischen Netzwerkes GEOFON aufgezeichnet. Etwa zwanzig Minuten später ereignete sich eine Katastrophe mit bis dahin noch nicht bekanntem Ausmaß. Der Meeresboden war über eine Länge von 1200 Kilometern durchgebrochen, mit einem Versatz von über zehn Metern. Ein gewaltiger Tsunami wurde ausgelöst, der von Indonesien über Thailand, Sri Lanka bis an der Ostküste Afrikas über 240 000 Menschen das Leben kostete. Der Initiator von SeisComP, Winfried Hanka: „Wir hatten das Beben damals über unsere Software SeisComP bereits nach 12 Minuten automatisch analysiert, allerdings noch mit deutlich unterschätzter Magnitude. Damit wussten wir von dem Beben zwar bereits zehn Minuten vor der Ankunft des Tsunami in Aceh, aber eine Warnung wäre wegen der fehlenden Strukturen in Indonesien nicht möglich gewesen.“

Description: Diese Dokumentation beschäftigt sich mit der Baugeschichte des Meridianhauses im Ensemble des Observatoriums für Winkelmessungen des Magnetisch-Geodätischen Instituts auf dem Telegrafenberg bei Potsdam.

Description: Wieviel Prozent Silizium, Lithium und Kupfer sind in einer Gesteinsprobe enthalten? Über unterschiedlich analytische Verfahren lassen sich alle Bestandteile einer Gesteinsprobe exakt bestimmen. Aber sind diese Ergebnisse überhaupt vergleichbar? „Das ist wirklich ein großes Problem“, sagt Michael Wiedenbeck, Geochemiker am GFZ. „Das Dilemma besteht darin, dass die Ergebnisse von jedem Labor ganz häufig auf eigenen Referenzen beruhen. Damit sind die Werte aus den Veröffentlichungen oft nicht vergleichbar.“

Description: 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.

Description: 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.

Description: 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.

Description: Wasser benetzt die Erdoberfläche, versickert im Boden, sammelt sich im Grundwasser und fließt in Bächen. Diese Fakten sind allgemein bekannt, doch um wie viel Wasser es sich dabei handelt, kann bisher meist nur ungenau bestimmt werden. Im Projekt HYGRA versuchen Benjamin Creutzfeldt, Andreas Güntner und Kollegen am "Geodätischen Observatorium Wettzell" im Bayerischen Wald die Schwankungen des Wasserhaushalts konkreter zu ermitteln. Sie nutzen hierfür Veränderungen der Gravitation, die mit dem Supraleitgravimeter des "Bundesamtes für Kartographie und Geodäsie (BKG)" gemessen werden. Creutzfeldt: "Es existiert eine starke Wechselbeziehung zwischen Hydrologie und Gravimetermessungen. So können wir an den Schwankungen der Gravitation die gespeicherte Menge von Wasser im Boden, im Grundwasser und in der Schneedecke erkennen."

Description: 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.