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  • English  (477)
  • 2005-2009  (477)
  • 1980-1984  (4)
  • 2006  (477)
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  • 1
    Monograph available for loan
    Monograph available for loan
    [Edgecumbe, N.Z.] : A. Muller
    Call number: M 15.89146
    Description / Table of Contents: An account of the results of the 2 March 1987 earthquake in the eastern Bay of Plenty and the aftermath's effects on the people and places on the Rangitaiki Plains
    Type of Medium: Monograph available for loan
    Pages: 223 S., , Ill.
    Language: English
    Branch Library: GFZ Library
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  • 2
    Monograph available for loan
    Monograph available for loan
    Stuttgart : Schweizerbart Science Publishers ; Volume 1, number 1 (1978)-
    Call number: M 18.91571
    Type of Medium: Monograph available for loan
    Pages: 134 Seiten
    ISSN: 2363-7196
    Series Statement: Global tectonics and metallogeny : special issue Vol. 10/2-4
    Classification:
    Tectonics
    Parallel Title: Erscheint auch als Global tectonics and metallogeny
    Language: English
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 3
    Monograph available for loan
    Monograph available for loan
    Garmisch-Partenkirchen : Institut für atmosphärische Umweltforschung der Fraunhofer- Gesellschaft
    Call number: MOP 44829 / Mitte
    Type of Medium: Monograph available for loan
    Pages: 25 S. , graph. Darst.
    Language: English
    Location: MOP - must be ordered
    Branch Library: GFZ Library
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  • 4
    Call number: 3/S 07.0034(2016)
    In: Annual report
    Type of Medium: Monograph available for loan
    Pages: 51 Seiten
    ISSN: 1865-6439 , 1865-6447
    Parallel Title: Erscheint auch als Annual report ... / Helmholtz Association of German Research Centres
    Language: English
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  • 5
  • 6
    Journal available for loan
    Journal available for loan
    Tübingen : Mohr Siebeck ; 1.1884 - 48.1931; N.F. 1.1932/33 - 10.1943/44(1945),3; 11.1948/49(1949) -
    Call number: ZS 22.95039
    Type of Medium: Journal available for loan
    Pages: Online-Ressource
    ISSN: 1614-0974 , 0015-2218 , 0015-2218
    Language: German , English
    Note: N.F. entfällt ab 57.2000. - Volltext auch als Teil einer Datenbank verfügbar , Ersch. ab 2000 in engl. Sprache mit dt. Hauptsacht.
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  • 7
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 8
    Publication Date: 2020-02-12
    Language: English
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  • 9
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 10
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 11
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 12
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 13
    Publication Date: 2020-04-17
    Language: English
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  • 14
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 15
    Publication Date: 2020-02-12
    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.
    Language: English
    Type: info:eu-repo/semantics/report
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  • 16
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    In:  Scientific Drilling
    Publication Date: 2020-02-12
    Language: English
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  • 17
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 18
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    IUGG Secretariat, CIRES Cooperative Institute for Research in Environmental Sciences, University of Colorado
    In:  IUGG Publications
    Publication Date: 2021-04-23
    Language: French , English
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  • 19
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    Deutsches GeoForschungsZentrum GFZ
    In:  Scientific Technical Report STR
    Publication Date: 2020-02-12
    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.
    Language: English
    Type: info:eu-repo/semantics/doctoralThesis
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  • 20
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    In:  Scientific Drilling
    Publication Date: 2020-02-12
    Language: English
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  • 21
    Publication Date: 2020-02-12
    Language: English
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  • 22
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 23
    Publication Date: 2020-02-12
    Language: English
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  • 24
    Publication Date: 2020-02-12
    Language: English
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  • 25
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    International Association of Meteorology and Atmospheric Sciences (IAMAS)
    In:  IAMAS Annual Report
    Publication Date: 2020-02-12
    Language: English
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  • 26
    Publication Date: 2020-02-12
    Language: English
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  • 27
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    In:  Scientific Drilling
    Publication Date: 2020-02-12
    Language: English
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  • 28
    Publication Date: 2020-02-12
    Language: English
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  • 29
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 30
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    In:  Geophysical Journal International
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 31
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    International Association of Hydrological Sciences (IAHS)
    In:  IAHS Annual Report
    Publication Date: 2020-02-12
    Language: English
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  • 32
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 33
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 34
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    Deutsches GeoForschungsZentrum GFZ
    In:  Scientific Technical Report STR
    Publication Date: 2020-02-12
    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.
    Language: English
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  • 35
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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  • 36
    Publication Date: 2020-02-12
    Description: We present evidence for significant deviations of the true instrument gain from that reported for several modern broad-band permanent seismograph stations. Our result derives from a systematic comparison of observed and synthetic long-period seismograms for approximately 600 large earthquakes. Seismograms were collected from globally distributed stations and analyzed using the centroid-moment-tensor (CMT) algorithm for estimating earthquake parameters. Following the source inversion, synthetic seismograms corresponding to the final earthquake parameters were compared with the observed seismograms and an optimal amplitude-scaling coefficient for each seismogram was determined. Scaling coefficients for earthquakes occurring in a given calendar year were then averaged to investigate the temporal stability of instrument gain. Data for up to 15 years (1990–2004) for more than 200 stations were processed. Most stations show good agreement (±10%) between the observed and reported gains. A small number of stations display a larger constant offset in the gain, probably caused by errors in the reported absolute gain or, potentially, by unmodeled systematic effects resulting from the Earth's lateral heterogeneity. The existence of errors in the reported long-period gain is confirmed through a station-by-station comparison with results from an independent analysis of station-gain bias at similar periods. More than 15 stations display significant reductions in the true long-period gain that occur gradually over several months to a few years. At ∼250-s period, these changes are as large as 50% of the reported gain. The changes are smaller at shorter periods, suggesting a frequency-dependent modification of the instrument response. All of the affected stations showing a time-dependent deterioration are equipped with the Streckeisen STS-1 seismometer, suggesting a common cause for the observed behavior.
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  • 37
    Publication Date: 2020-02-12
    Description: [1] We present a new three-dimensional Sv wave speed and azimuthal anisotropy model for the upper mantle of eastern Asia constrained by the analysis of more than 17,000 vertical component multimode Rayleigh wave seismograms. This data set allows us to build an upper mantle model for Asia with a horizontal resolution of a few hundred kilometers extending to ∼400 km depth. At 75–100 km depth, there is approximately ±9% wave speed perturbation from the “smoothed PREM” reference model used in our analysis, and the pattern of azimuthal anisotropy is complex. Both the amplitude of the Sv wave speed heterogeneity and the complexity and amplitude of the azimuthal anisotropy decrease with depth. Above ∼200 km depth the upper mantle structure of the model correlates with surface geology and tectonics; below ∼200 km depth the structures primarily reflect the advection of material in the upper mantle. Since shear wave speed is principally controlled by temperature rather than by composition, Vs(z) can be used to calculate the temperature T(z), and hence map the lithospheric thickness. We use the relationship of Priestley and McKenzie to produce a contour map of the lithospheric thickness of eastern Asia from the surface wave tomography. This shows an extensive region of thick lithosphere beneath the Siberian Platform and the West Siberian Basin that extends to the European Platform, forming the stable Eurasian craton or core. The eastern portion of the Eurasian craton has controlled the geometry of continental deformation and the distribution of kimberlites in eastern Asia.
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  • 38
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    In:  Scientific Drilling
    Publication Date: 2020-02-12
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  • 39
    Publication Date: 2020-02-12
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  • 40
    Publication Date: 2020-02-12
    Description: Detailed images of the lithosphere beneath the western Bohemian Massif were obtained by analysis of more than 8500 P receiver functions. At the intersection of Regensburg-Leipzig-Rostock zone and Eger Rift, crustal thickness decreases to 26 km from approx. 31 km in the surroundings. The receiver functions display a positive phase at about 6 s delay time and a strong negative phase at 7 to 8 s, which coincides with an area of Moho updoming, CO2 mantle-derived degassing and earthquake swarm activity. These phases can be modeled by a velocity increase at 50 km and a velocity decrease at 65 km depth. The velocity decrease, observed over an area of 5300 km2, gives evidence for local asthenospheric updoming and/or a confined body of partial melt, which might be the cause for high CO2 mantle fluid flow and earthquake swarm activity in this recently nonvolcanic, intracontinental rift area.
    Keywords: 550 - Earth sciences
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  • 41
    Publication Date: 2020-02-12
    Description: Compound-specific isotope analysis has become an important tool in environmental studies and is an especially powerful way to evaluate biodegradation of hydrocarbons. Here, carbon isotope ratios of light hydrocarbons were used to characterise in-reservoir biodegradation in the Gullfaks oil field, offshore Norway. Increasing biodegradation, as characterised, for example, by increasing concentration ratios of Pr/n-C17 and Ph/n-C18, and decreasing concentrations of individual light hydrocarbons were correlated to 13C-enrichment of the light hydrocarbons. The δ13C values of C4 to C9n-alkanes increase by 7–3‰ within the six oil samples from the Brent Group of the Gullfaks oil field, slight changes (1–3‰) being observed for several branched alkanes and benzene, whereas no change (〈1‰) in δ13C occurs for cyclohexane, methylcyclohexane, and toluene. Application of the Rayleigh equation demonstrated high to fair correlation of concentration and isotope data of i- and n-pentane, n-hexane, and n-heptane, documenting that biodegradation in reservoirs can be described by the Rayleigh model. Using the appropriate isotope fractionation factor of n-hexane, derived from laboratory experiments, quantification of the loss of this petroleum constituent due to biodegradation is possible. Toluene, which is known to be highly susceptible to biodegradation, is not degraded within the Gullfaks oil field, implying that the local microbial community exhibits rather pronounced substrate specificities. The evaluation of combined molecular and isotopic data expands our understanding of the anaerobic degradation processes within this oil field and provides insight into the degradative capabilities of the microorganisms. Additionally, isotope analysis of unbiodegraded to slightly biodegraded crude oils from several oil fields surrounding Gullfaks illustrates the heterogeneity in isotopic composition of the light hydrocarbons due to source effects. This indicates that both source and also maturity effects have to be well constrained when using compound-specific isotope analysis for the assessment of biodegradation.
    Keywords: 550 - Earth sciences
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  • 42
    Publication Date: 2020-02-12
    Description: As part of the South American Geodynamic Activities project we observed the present day deformation field in the territories of Chile and Argentina using the Global Positioning System. The results clearly show that the earthquake cycle dominates the contemporary surface deformation of the central and southern Andes. Compared to geological timescales, the transient elastic deformation related to subduction earthquakes presents a short-term signal which can be explained by interseismic, coseismic, and postseismic phases of interplate thrust earthquakes. We constructed the Andean Elastic Dislocation Model (AEDM) in order to subtract the interseismic loading from the observed velocities. The estimated parameters of the AEDM, and the amount and depth of coupling between the subducting Nazca and overriding South American Plates, represent long-term features and show that the seismogenic interface between both plates is fully locked and that the depth of coupling increases from north to south. The prominent signals in the residual velocity field (i.e. observed velocities minus AEDM) are obviously due to postseismic relaxation processes; they are visible in the area of the 1995 Mw 8.0 Antofagasta earthquake and in the area of the 1960 Mw 9.5 Valdivia earthquake. Although postseismic deformations, compared to geologic timescales, are short-term signals, those signals are valuable constraints on important long-term features of Andean evolution, i.e., the viscosity of the upper mantle and lower crust. The observed surface data are best fitted with a three-dimensional finite element model in which we incorporate a mantle viscosity of 4 × 1019 Pa s. The most obvious long-term deformation signal is manifested in the back-arc of the subduction zone where the Brazilian Shield thrusts beneath the Subandean zone. The style and amount of backarc shortening changes along strike of the orogen, increasing from zero in the south (latitude 〈 −38° S) to values in the order of 10 mm yr−1 close to the Bolivian Orocline. In the fore-arc, whilst we see indications for long-term E-W extension, we did not find any apparent slip partitioning. In addition to this long-term signal, we suggest that the asymmetry of interseismic and coseismic deformation may lead to tectonic structures in the fore-arc. If the coseismic deformation does not release all of the accumulated deformation, then, over many earthquake cycles, part of the interseismic deformation may be transformed into permanent long-term plastic deformation.
    Keywords: 550 - Earth sciences
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  • 43
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    In:  The Andes - Active Subduction Orogeny | Frontiers in Earth Sciences
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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  • 44
    Publication Date: 2020-02-12
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  • 45
    Publication Date: 2020-02-12
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  • 46
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    International Association of Geomagnetism and Aeronomy (IAGA)
    In:  IAGA Annual Report
    Publication Date: 2020-02-12
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  • 47
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    In:  Scientific Drilling
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  • 48
    Publication Date: 2020-02-12
    Description: [1] We compare observations of long-period seismic surface waves and free oscillations recorded by high-resolution long-base fluid tube tiltmeters and by nearby broadband seismometers after large earthquakes. The quality of the tiltmeter data is comparable to that of the best horizontal component seismic data, recording some of the gravest free oscillations of the Earth, as well as successive passages of seismic surface waves circling the globe. We compare the observations with theoretical seismograms and with theoretical tilt. The predicted and observed surface wave tilt waveforms are very similar provided that we take into account horizontal acceleration effects on the tiltmeter. Phase and amplitude anomalies between the waveforms are well explained by the theoretical transfer function of the instrument. Likewise, observed horizontal seismograms converted into tilt match the tiltmeter data very well. Long-base fluid tube tiltmeters could potentially contribute to obtain high-quality measurements of the long-period seismic spectrum.
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  • 49
    Publication Date: 2020-02-12
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  • 50
    Publication Date: 2020-02-12
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  • 51
    Publication Date: 2020-02-12
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  • 52
    Publication Date: 2020-02-12
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  • 53
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    In:  Scientific Drilling
    Publication Date: 2020-02-12
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  • 54
    Publication Date: 2020-02-12
    Description: We employ P to S converted waveforms to investigate effects of the hot mantle plume on seismic discontinuities of the crust and upper mantle. We observe the Moho at depths between 13 and 17 km, regionally covered by a strong shallow intracrustal converted phase. Coherent phases on the transverse component indicate either dipping interfaces, 3-D heterogeneities or lower crustal anisotropy. We find anomalies related to discontinuities in the upper mantle down to the transition zone evidently related to the hot mantle plume. Lithospheric thinning is confirmed in greater detail than previously reported by Li et al., and we determine the dimensions of the low-velocity zone within the asthenosphere with greater accuracy. Our study mainly focuses on the temperature-pressure dependent discontinuities of the upper mantle transition zone. Effects of the hot diapir on the depths of mineral phase transitions are verified at both major interfaces at 410 and 660 km. We determine a plume radius of about 200 km at the 660 km discontinuity with a core zone of about 120 km radius. The plume conduit is located southwest of Big Island. A conduit tilted in the northeast direction is required in the upper mantle to explain the observations. The determined positions of deflections of the discontinuities support the hypothesis of decoupled upper and lower mantle convection.
    Keywords: 550 - Earth sciences
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  • 55
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    In:  Scientific Drilling
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  • 56
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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  • 57
    Publication Date: 2020-02-12
    Description: In the south-eastern corner of the Tyrrhenian basin, in the central Mediterranean Sea, a tight alignment of earthquakes along a well-defined Benioff zone marks one of the narrowest active trenches worldwide, where one of the last fragment of the former Tethys ocean is consumed. Seismic tomography furnishes snapshot images of the present-day position of this slab, and seismic anisotropy allows to reconstruct the past kinematics of the subduction process. Using seismic anisotropy fast directions as a proxy for the present and past mantle flow, we look backward for the seismic traces of the slab motion through the western-central Mediterranean mantle, from the starting locus of subduction toward its present day position. The result of combining independent data sets provides a coherent pattern of anisotropy that illustrates an example of slab rollback from its initiation point to its present-day position.
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  • 58
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    Deutsches GeoForschungsZentrum GFZ
    In:  Scientific Technical Report STR
    Publication Date: 2020-02-12
    Description: Based on the physical processes governing the motion and dynamics of poly-thermal ice sheets, we distinguish two regions; the cold region, where the ice temperature is below the melting point, and the temperate region, where the ice temperature is exactly equal to the melting point, leading to the presence of a water fraction. This work focuses on the analysis and description of the temperate zone on the basis of rational thermo-dynamics of reacting mixtures. The balance laws for the ice-water mixture, that is the mass balance, balance of linear and angular momenta, energy and entropy, are discussed. A physical model for a polythermal ice sheet is then established, including appropriate boundary and transition conditions. The resulting formulation is convenient for numerical implementation. Numerical examples are carried out for a stationary 2-D case and the results of the present and traditional formulations are compared.
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  • 59
    Publication Date: 2020-02-12
    Description: Combined P and S receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the Aegean region are used to map the geometry of the subducted African and the overriding Aegean plates. We image the Moho of the subducting African plate at depths ranging from 40 km beneath southern Crete and the western Peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern Greece. However, the dip of the Moho of the subducting African plate is shallower beneath the Peloponnesus than beneath Crete and Rhodes and flattens out beneath the northern Aegean. Observed P-to-S conversions at stations located in the forearc indicate a reversed velocity contrast at the Moho boundary of the Aegean plate, whereas this boundary is observed as a normal velocity contrast by the S-to-P conversions. Our modeling suggests that the presence of a large amount of serpentinite (more than 30%) in the forearc mantle wedge, which generally occurs in the subduction zones, may be the reason for the reverse sign of the P-to-S conversion coefficient. Moho depths for the Aegean plate show that the southern part of the Aegean (crustal thickness of 20–22 km) has been strongly influenced by extension, while the northern Aegean Sea, which at present undergoes the highest crustal deformation, shows a relatively thicker crust (25–28 km). This may imply a recent initiation of the present kinematics in the Aegean. Western Greece (crustal thickness of 32–40 km) is unaffected by the recent extension but underwent crustal thickening during the Hellenides Mountains building event. The depths of the Aegean Moho beneath the margin of the Peloponnesus and Crete (25–28 and 25–33 km, respectively) show that these areas are also likely to be affected by the Aegean extension, even though the Cyclades (crustal thickness of 26–30 km) were not significantly involved in this episode. The Aegean lithosphere-asthenosphere boundary (LAB) mapped with S receiver functions is about 150 km deep beneath mainland Greece, whereas the LAB of the subducted African plate dips from 100 km beneath Crete and the southern Aegean Sea to about 225 km under the volcanic arc. This implies a thickness of 60–65 km for the subducted African lithosphere, suggesting that the Aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the Cyclades.
    Keywords: 550 - Earth sciences
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  • 60
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    Deutsches GeoForschungsZentrum GFZ
    In:  Scientific Technical Report STR
    Publication Date: 2020-02-12
    Description: This work describes the results of seismological field campaigns and experiments using combined seismic networks of varying geometries such as a combined seismic downhole and surface network or a combined temporary local and permanent regional network. The networks were deployed in different tectonic environments, i.e. in a stable intraplate surrounding, at a plate boundary along a major transform fault zone and in forearc and backarc settings of a subduction zone to record different types of seismicity (induced earthquakes, aftershocks, subduction-related seismicity). Recording periods are typically several months. The basic ideas behind all the different experiments and studies presented here can be described as follows: In a first step, a state of the art seismic network is designed and deployed in a selected area to record local (micro)seismic activity at low magnitude detection threshold. The acquired data base is then evaluated using standard processing techniques to generate a proper hypocenter catalog for the area of investigation during the observational period. This period might be extended (at higher magnitude detection threshold) through re-evaluating and calibrating earlier hypocenter catalogs gained from records of regional permanent networks. This new catalog for the selected region then forms the base for further evaluation using different approaches one of which is the determination of fault plane solutions in order to determine the local stress field orientation and relate it to the WSM data or information on regional displacement fields determined from GPS recordings.
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  • 61
    Publication Date: 2020-02-12
    Description: We present a new upper mantle seismic model for southern Africa based on the fitting of a large (3622 waveforms) multi-mode surface wave data set with propagation paths significantly shorter (≤ 6000 km) than those in globally-derived surface wave models. The seismic lithosphere beneath the cratonic region of southern Africa in this model is about 175 ± 25 km thick, consistent with other recent surface wave models, but significantly thinner than indicated by teleseismic body-wave tomography. We determine the in situ geotherm from kimberlite nodules from beneath the same region and find the thermal lithosphere model that best fits the nodule data has a mechanical boundary layer thickness of 186 km and a thermal lithosphere thickness of 204 km, in very good agreement with the seismic measurement. The shear wave velocity determined from analyzes of the kimberlite nodule compositions agree with the seismic shear wave velocity to a depth of ∼150 km. However, the shear wave velocity decrease at the base of the lid seen in the seismic model does not correspond to a change in mineralogy. Recent experimental studies of the shear wave velocity in olivine as a function of temperature and period of oscillation demonstrate that this wave speed decrease can result from grain boundary relaxation at high temperatures at the period of seismic waves. This decrease in velocity occurs where the mantle temperature is close to the melting temperature (within ∼100 °C).
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  • 62
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    In:  Bulletin of the Seismological Society of America
    Publication Date: 2020-02-12
    Description: We develop an algorithm for the detection and location of seismic sources using intermediate-period (35–150 sec) surface waves recorded on a global array of stations. Continuous vertical seismic waveforms from the global network are collected and a 4° × 4° global grid of target locations is defined. For each target location and each station, a surface-wave propagation operator is deconvolved from the seismogram to restore any source pulse present. The envelope of the seismogram is calculated and cross correlated with a theoretical source-pulse shape. The resulting waveforms are stacked to improve signal-to-noise characteristics, and the quality, strength, and timing of the potential detection are determined. When a successful event detection is made, a finer grid is applied to locate the event with greater precision. We apply the algorithm systematically for the period 1993–2003 and catalog the events. Approximately 2000 events are detected and located for each year and 98% of shallow events in the Harvard Centroid Moment Tensor (cmt) catalog are detected and located by the new algorithm. A comparison of 9482 events common to the two catalogs allows the detection strength to be calibrated against the cmt moment magnitude. All detected events have estimated moment magnitudes Mw 〉4.5. In each year, approximately 100 events not listed in other global seismicity catalogs are detected and located. Many of these events lie along the ridge-transform plate boundaries in the Southern Hemisphere and may be regular earthquakes that have gone undetected because of poor station coverage. Other events, located in areas where global and regional networks provide good coverage, are potentially anomalous and may have escaped detection as a result of their unusual source properties.
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  • 63
    Publication Date: 2020-02-12
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  • 64
    Publication Date: 2020-02-12
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  • 65
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    In:  Annals of Geophysics
    Publication Date: 2020-02-12
    Description: The ocean exerts a pervasive influence on Earths environment. It is therefore important that we learn how this system operates (NRC, 1998b; 1999). For example, the ocean is an important regulator of climate change (e.g., IPCC, 1995). Understanding the link between natural and anthropogenic climate change and ocean circulation is essential for predicting the magnitude and impact of future changes in Earths climate. Understanding the ocean, and the complex physical, biological, chemical, and geological systems operating within it, should be an important goal for the opening decades of the 21st century. Another fundamental reason for increasing our understanding of ocean systems is that the global economy is highly dependent on the ocean (e.g., for tourism, fisheries, hydrocarbons, and mineral resources) (Summerhayes, 1996). The establishment of a global network of seafloor observatories will help to provide the means to accomplish this goal. These observatories will have power and communication capabilities and will provide support for spatially distributed sensing systems and mobile platforms. Sensors and instruments will potentially collect data from above the air-sea interface to below the seafloor. Seafloor observatories will also be a powerful complement to satellite measurement systems by providing the ability to collect vertically distributed measurements within the water column for use with the spatial measurements acquired by satellites while also providing the capability to calibrate remotely sensed satellite measurements (NRC, 2000). Ocean observatory science has already had major successes. For example the TAO array has enabled the detection, understanding and prediction of El Niño events (e.g., Fujimoto et al., 2003). This paper is a world-wide review of the new emerging Seafloor Observatory Science, and describes both the scientific motivations for seafloor observatories and the technical solutions applied to their architecture. A description of world-wide past and ongoing experiments, as well as concepts presently under study, is also given, with particular attention to European projects and to the Italian contribution. Finally, there is a discussion on Seafloor Observatory Science perspectives.
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  • 66
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    In:  7. Forum und Gefahrentag des DKKV in Eschborn (GTZ) - Vorträge
    Publication Date: 2020-02-12
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  • 67
    Publication Date: 2020-02-12
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  • 68
    Publication Date: 2020-02-12
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  • 69
    Publication Date: 2020-02-12
    Description: The INGV-Harvard European-Mediterranean Regional Centroid Moment Tensor (RCMT) Catalog collects solutions routinely computed since 1997 for earthquakes with moderate magnitude (4.5≤M≤5.5) in the Mediterranean region. The database represents an extension to smaller magnitudes of the Harvard global CMT catalog, based on analysis of seismograms recorded at regional distance, and modeling of intermediate period surface waves. The catalog includes about 600 events, 200 of which in the Italian region. This study extends the catalog back in time, for the Italian region, as long as made possible by available digital data – i.e. since 1977 – with the same analysis and inversion method used for current seismicity. As a result, we present here 65 new moment tensors, for years between 1977 and 1997. These solutions represent 45% of the total number of events analyzed, the existing seismograms being often too scarce to allow a stable solution. The new dataset includes events in many seismic zones where moderate seismicity had previously been scarcely documented, e.g., the Po Plain, the Central to Southern Apennines and the Adriatic Sea. The complete dataset, including previously determined RCMTs and CMTs, represents the seismic deformation in the Italian area during the last 25 years.
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  • 70
    Publication Date: 2020-02-12
    Description: The volcanic arc of the Hellenic subduction zone with its four volcanic centers is of major relevance when evaluating the seismovolcanic hazard for the Aegean region. We present results from a 22-station temporary seismic network (CYCNET) in the central Hellenic Volcanic Arc (HVA). CYCNET recordings allow to analyze the level and spatio-temporal evolution of microseismic activity in this region for the first time. A total of 2175 events recorded between September 2002 and July 2004 are analyzed using statistical methods, cluster analysis and relative relocation techniques. We identify distinct regions with significantly varying spatio-temporal behavior of microseismicity. A large portion of the seismic activity within the upper crust is associated with the presence of islands representing horst structures that were generated during the major Oligocene extensional phase. In contrast, the central part of the Cyclades metamorphic core complex remains aseismic considering our magnitude threshold of 1.8 except one spot where events occur swarm-like and with highly similar waveforms. The highest activity in the study area was identified along the SW–NE striking Santorini–Amorgos zone. Within this zone the submarine Columbo volcano exhibits strong temporal variations of seismic activity on a high background level. This activity is interpreted to be directly linked to the magma reservoir and therein the migration of magma and fluids towards the surface. NE of Columbo where no volcanic activity has yet been reported we observe a similar seismicity pattern with small-scaled activity spots that might represent local pathways of upward migrating fluids or even developing volcanic activity within this zone of crustal weakness. In contrast, the Santorini and Milos volcanic complexes do not show significant temporal variations and low to moderate background activity, respectively. Relating our results to the distribution of historical earthquakes and the GPS-derived horizontal velocity field we conclude that the Santorini–Amorgos zone is presently in the state of right-lateral transtension reflecting a major structural boundary of the volcanic arc subdividing it into a seismically and volcanically quiet western and an active eastern part.
    Keywords: 550 - Earth sciences
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  • 71
    Publication Date: 2020-02-12
    Language: German , English
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  • 72
    Publication Date: 2020-02-12
    Description: Dynamite shots of the crustal-scale refraction seismic project ALP 2002 were recorded by an array of 40 seismological three-component stations on the TRANSALP profile. These observations provide a direct link between the two deep seismic projects. We report preliminary results obtained from these data. In a first approach, we verified the TRANSALP refraction seismic velocity model computing travel times for several shots and comparing them to the new observations. The results generally confirm this model. Significant first-break travel time differences in and near the Tauern Window are explained by anisotropy. Large-scale features of the model, particularly the Moho structure, seem to be continuous towards the east. Travel time residuals of wide-angle reflections indicate a slight eastward dip component of the Adriatic Moho.
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  • 73
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    IUGG Secretariat, CIRES Cooperative Institute for Research in Environmental Sciences, University of Colorado
    Publication Date: 2020-02-12
    Language: English
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  • 74
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    In:  Geophysical Journal International
    Publication Date: 2020-02-12
    Description: Teleseismic P-wave tomography has revealed a columnar low-velocity anomaly in the upper mantle below the volcanic Eifel region in western Germany extending to at least 400 km depth. Here we explore whether a geodynamically consistent model of a mantle plume can explain the observed traveltime residuals. We use a 3-D mantle convection code with temperature and pressure-dependent viscosity to generate a suite of model plumes that rise from the transition zone and spread below a stationary or drifting lithospheric plate. We use ray tracing to calculate synthetic travel times and vary the plume location, radius, temperature and the rate and direction of plate motion in order to fit the observed travel times. Our results show a fair correlation between synthetic and observed traveltime residuals. The presence of additional structures in the lithosphere and upper mantle of the Eifel region that are not covered by a simple plume model prevents a perfect fit of the observed seismological data and may bias to some degree the derived plume parameters. The traveltime anomalies are mainly caused by the plume stem with smaller contributions from the plume head. Models with and without an axisymetric plume head below the lithosphere fit the data almost equally well and we conclude that the absence of a plume head in tomographic images does not rule out its existence. In the best-fitting model the plume stem has a radius of 60 km and rises about 50 km to the SW of the quaternary volcanic field below a lithosphere that this slowly moving in the NNE direction. The temperature of the plume and its flux cannot be constrained tightly from our model results, but combining them with other constraints we estimate an excess temperature of ∼200°C and a buoyancy flux of 500–1000 kg s−1.
    Language: English
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  • 75
    Publication Date: 2020-02-12
    Language: English
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  • 76
    Publication Date: 2020-02-12
    Description: Seismic anisotropy, a property linked to the texture of the mantle rock, should be distributed with depth along the trace of the Dead Sea Rift (DSR), owing to a combination of present day and ancient tectonics. Using data from four permanent and one temporary seismic observatories we evaluate birefringence (splitting) of 91 teleseismic core-refracted shear waves, primarily SKS phases. We find significant levels of birefringence in the bulk of observed phases. We also find that birefringence parameters (fast directions and delays) vary as a function of source–receiver geometry. Notably, the pattern of this directional variation in birefringence is quite similar at all sites we have examined. We interpret observed birefringence in SKS phases in terms of one- and two-layer models. Single-layer models for all stations exhibit a fast polarization oriented 12–19° east of north, with anisotropy sufficient to generate 1.3-s time delay. We find strong evidence for at least two distinct anisotropic layers. For the two layer models, the upper layers resemble the single-layer models, showing near-north fast polarizations and delays on the order of 1 s. Three out of four sites show fast polarizations in the lower layer that strike 50–80° CW from north with time delays 0.3–0.6 s. One site, at the northern end of the DSR, displays a higher degree of anisotropy in the lower layer, and a more northerly fast polarization. Overall, the lower layers at all sites appear to be consistent with the deformation caused by plate motion relative to the asthenosphere. The fabric in the upper layer is sub-parallel to the present-day transcurrent motion on the DSR, but also matches the typical orientation of lithospheric seismic anisotropy in the Arabian shield. Our overall conclusion is that the impact of the DSR on the rock fabric of the mantle lithosphere is probably quite weak.
    Language: English
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  • 77
    Publication Date: 2020-02-12
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  • 78
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    Deutsches GeoForschungsZentrum GFZ
    In:  Scientific Technical Report STR
    Publication Date: 2020-02-12
    Language: English
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  • 79
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    International Association of Seismology and Physics of the Earth's Interior (IASPEI)
    In:  IASPEI Annual Report
    Publication Date: 2020-02-12
    Language: English
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  • 80
    Publication Date: 2020-02-12
    Language: English
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  • 81
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    In:  Scientific Drilling
    Publication Date: 2020-02-12
    Language: English
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  • 82
    Publication Date: 2020-02-12
    Description: A seismicity and stress field analysis of a region in NE Bavaria reveals a complex picture of seismic dislocation. The magnitudes are generally low, the strongest event recorded had a magnitude of 2.3. In the southern part of the area investigated, earthquakes occur very rarely. During the observation period of approximately four years, only four events, two of them forming a doublet, were recorded. Hypocentral depths in the southern part are considerably great (15 to 17 km) and indicate a mafic lower crust. The seismicity of the Marktredwitz area, located in the western extension of the Eger rift, is dominated by earthquake swarms that are strongly clustered in space and time. The swarms occurred at depths between 10 and 14 km. Precise relative relocations show clear planar arrangements of the hypocentres and enable to identify the orientation of active fault planes. A comparison of the structural and geomorphological settings reveals major similarities in the occurrence of earthquake swarms compared to the situation in the bordering Vogtland/NW-Bohemia swarm area.
    Language: English
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  • 83
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    DWA
    In:  Forum für Hydrologie und Wasserbewirtschaftung
    Publication Date: 2020-02-12
    Description: Der Band dokumentiert ausführlich 17 Referate und Diskussionsbeiträge des Workshops, der im Rahmen des BMBF-Förderschwerpunkt "Risikomanagement extremer Hochwasserereignisse" 2006 an der Univ. Trier veranstaltet wurde. Die Beiträge lassen sich 5 thematischen Blöcken zuordnen: 1. Konzepten (vorgestellt werden u.a. Fuzzy-Modelle) und 2. Anwendungsbeispielen und Modellkalibrierung von Niederschlag-Abfluss-Modellen. Innerhalb dieser Session wird ein sehr breites Spektrum an konkreten Modellanwendungen vorgestellt. Der 3. Themenblock befasst sich mit der Modellkopplung und der Integration von Fernerkundungsdaten, der 4. mit Extremen Abflüssen: Herleitung, Simulation, Bemessung, der 5. Themenblock mit Modellidentifikation und Modellunsicherheit.
    Language: German , English
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  • 84
    Publication Date: 2020-02-12
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  • 85
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    In:  The Andes - Active Subduction Orogeny | Frontiers in Earth Sciences
    Publication Date: 2020-02-12
    Description: The Andes were formed by Cenozoic tectonic shortening of the South American plate margin overriding the subducting Nazca Plate. Using coupled, thermo-mechanical, numerical modeling of the dynamic interaction between subducting and overriding plates, we searched for factors controlling the intensity of the tectonic shortening. From our modeling, constrained by geological and geophysical observations, we infer that the most important factor was fast and accelerating (from 2 to 3 cm yr(hoch)-1) westward drift of the South American Plate, whereas possible changes in the convergence rate were not as important. Other important factors are the crustal structure of the overriding plate and the shear coupling at the plate interface. The model in which the South American Plate has a thick (40-45 km at 35 Ma) crust and relatively high friction coefficient (0.05) at the Nazca-South American plate interface generates more than 300 km of tectonic shortening over the past 35 million years and replicates well the crustal structure and evolution of the high Central Andes, However, modeling does not confirm that possible climate-controlled changes to the sedimentary trench-fill during the last 30 million years might have significantly influenced the upperplate shortening rate. The model with initially thinner (less than 40 km) continental crust and a lower friction coefficient (less than 0.015) results in less than 40 ikm of shortening in the South American Plate, replicating the situation in the Southern Andes. During upper-plate deformation, the processes that cause a reduction in lithospheric strength and an increase in interplate coupling are particularly important. The most significant of these processes appears to be: (1) delamination of the lower crust and mantle lithosphere, driven by gabbro-eclogite transformation in the thickening lower crust, and (2) mechanical failure of the foreland sediments. The modeling demonstrates that delaminating lithosphere interacts with subduction-zone corner flow, influencing both the rate of tectonic shortening and magmatic-arc productivity, and suggests an anti-correlation between these two parameters. Our model also predicts that the down-dip limit of the frictional coupling domain between the Nazca and South American Plates should be ~15-20 km deeper in the Southern Andes (south of 28° S) compared to the high Central Andes, which is consistent with GPS and seismological observations.
    Keywords: 550 - Earth sciences
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  • 86
    Publication Date: 2020-02-12
    Description: This paper combines observations of seismicity, gravity, topography and thermal and velocity structures to investigate the rheological properties of the lithosphere in the Lake Baikal region. We examine the seismogenic thickness (Ts) using 25 earthquakes of Mw 5.1–7.1, whose full source parameters have been determined by inversion of teleseismic waveforms, 13 of which are presented here for the first time. These 25 events, plus six others (Mw 5.0–5.8) whose depths are well constrained, show that moderate earthquakes occur at depths up to ∼30 km in the northeast Baikal rift. Based on the teleseismic waveform modelling results and published relocations of microearthquakes using regional networks, we conclude that the mantle is not a significant source of seismicity in the Baikal region. Using the admittance between free-air gravity and topography, we estimate the effective elastic thickness (Te) in the region to be between 5 and 20 km. Nowhere do the data require that Te 〉 Ts, consistent with the simple interpretation that the long-term strength of the lithosphere resides in its seismogenic layer. A weak mantle in the Baikal region can be explained by its high temperature, which we estimate by combining local geotherm estimates with the regional upper mantle velocity structure, obtained from fundamental and higher-mode surface waves. Geotherms are fitted to pressure and temperature estimates from mantle nodules at four sites, both within and outside the Siberian shield. In order to constrain the temperatures at the Moho, we estimated crustal thicknesses using teleseismic receiver functions. Moho temperatures are estimated to exceed ∼550°C beneath the Siberian shield and are higher in the more recently deformed mountain belts to the south. Based on a reassessment of oceanic geotherms and seismicity, it seems likely, therefore, that the mantle in the Baikal region is too hot to be a source of long-term strength. This is consistent with the recent suggestion that the distribution of mantle seismicity in both the oceans and the continents is dependent on temperature alone. Finally, we note that results from S-wave tomography studies, combined with the observed locations of rift-related earthquakes, lead us to suspect that the frequently published position of the edge to the Siberian shield at the surface provides a poor description of that same boundary at depth.
    Language: English
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  • 87
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    In:  Geophysical Journal International
    Publication Date: 2020-02-12
    Description: Receiver functions (RF) are used to investigate the upper mantle structure beneath the Eifel, the youngest volcanic area of Central Europe. Data from 96 teleseismic events recorded by 242 seismological stations from permanent and a temporary network has been analysed. The temporary network operated from 1997 November to 1998 June and covered an area of approximately 400 × 250 km2 centred on the Eifel volcanic fields. The average Moho depth in the Eifel is approximately 30 km, thinning to ca. 28 km under the Eifel volcanic fields. RF images suggest the existence of a low velocity zone at about 60–90 km depth under the West Eifel. This observation is supported by P- and S-wave tomographic results and absorption (but the array aperture limits the resolution of the tomographic methods to the upper 400 km). There are also indications for a zone of elevated velocities at around 200 km depth, again in agreement with S-wave and absorption tomographic results. This anomaly is not visible in P-wave tomography and could be due to S-wave anisotropy. The RF anomalies at the Moho, at 60–90 km, and near 200 km depth have a lateral extent of about 100 km. The 410 km discontinuity under the Eifel is depressed by 15–25 km, which could be explained by a maximum temperature increase of +200°C to +300°C. In the 3-D RF image of the Eifel Plume we also notice two additional currently unexplained conversions between 410 and 550 km depth. They could represent remnants of previous subduction or anomalies due to delayed phase changes. The lateral extent of these conversions and the depression of the 410 km discontinuity is about 200 km. The 660 km discontinuity does not show any depth deviation from its expected value. Our observations are consistent with interpretation in terms of an upper mantle plume but they do not rule out connections to processes at larger depth.
    Keywords: 550 - Earth sciences
    Language: English
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  • 88
    Publication Date: 2020-02-12
    Description: The Variscan orogeny, resulting from the collision of Laurussia with Gondwana to form the supercontinent of Pangaea, was followed by a period of crustal instability and re-equilibration throughout Western and Central Europe. An extensive and significant phase of Permo-Carboniferous magmatism led to the extrusion of thick volcanic successions across the region (e.g. NE German Basin, NW part of the Polish Basin, Oslo Rift, northern Spain). Coeval transtensional activity led to the formation of more than 70 rift basins across the region. The various basins differ in terms of their form and infill according to their position relative to the Variscan orogen (i.e. internide or externide location) and to the controls that acted on basin development (e.g. basement structure configuration). This paper provides an overview of a variety of basin types, to more fully explore the controls upon the tectonomagmatic-sedimentary evolution of these important basins.
    Language: English
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  • 89
    Publication Date: 2020-02-12
    Language: English
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  • 90
    Publication Date: 2020-11-25
    Description: This paper describes an unsupervised classifier for polarimetric interferometric SAR (PolInSAR) data. Expectation maximisation is used to estimate class parameters that maximise the probability of a dataset for a given number of classes. Polarimetric information, in the form of coherency matrices, and interferometric information, in the form of complex coherences, is taken into account. Phase differentials between complex coherences in different polarisation bases are used to make the classifier sensitive to the vertical structure of the scene under observation, and a distribution of such phase differentials is developed. The classifier is self initialising in that it does not rely on decompositions or thresholds. Classification results based on real data are presented and discussed
    Language: English
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  • 91
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    Deutsches GeoForschungsZentrum GFZ
    In:  Scientific Technical Report STR
    Publication Date: 2021-08-21
    Description: A set of 59 seismological stations was deployed in the Central Andes region at 21°S (Chile-Bolivia) along a profile ~600 km long and were operated between 2002 and 2004. The teleseismic tomographic images (from P- and S- waves) show low-velocity anomalies that are interpreted as the effects of melting or fluids at both flanks of the Altiplano plateau. Beneath the Central Volcanic Zone (CVZ) a low-velocity anomaly is interpreted to be caused by fluids that are the origin of the volcanic material from the CVZ. A low-velocity anomaly in the upper crust is interpreted as the Altiplano Low-Velocity Zone that appears to extend as far to the east as the Eastern Cordillera. A high-velocity body between 100 km and 150 km depth is interpreted as being part of the old cold lithosphere that detached from the base of the crust. The Brazilian Shield is thought to be responsible for the strong high-velocity anomaly on the eastern side of the Central Andes. In addition, another set of 19 stations was deployed in the southern Argentine Puna along a profile ~200 km long and were run over the same period of time (2002-2004). The intention was to study the crustal thickness at 25.5°S, where delamination of the lithosphere was proposed to explain the higher elevation of the Puna plateau. Beneath the plateau a negative velocity anomaly is observed and interpreted here as being the location of fluid transfer between the deeper and shallower portions of the crust, that emanate from the Benioff zone at depths of ~200 km. This anomaly clearly divides in two branches: one to the west towards the volcanic arc (CVZ) and the other to the east where the back-arc volcanoes are located. On their way to lower depths, the fluid paths are probably influenced by the presence of nearby isotherms. The bifurcation of the ascending path could be related to the presence of the lithosphere-asthenosphere boundary (LAB) at ~100-130 km. Based on our observations, the type and form of the anomaly, it is possible to propose the presence of a return-flow type model for fluid ascent in contraposition to the assumed corner-flow model usually proposed for the Andes. The fluids that cause the seismic anomalies beneath the Puna plateau are generated at deeper levels in the asthenosphere and ascend parallel to the oceanic slab in the manner of a return-flow. In the crust and beneath the Salar de Antofalla (SA), a high-velocity block with seismic activity is interpreted as part of the old and cold Palaeozoic magmatic arc (Faja Eruptiva de la Puna Occidental). The presence of this block is may be responsible for the distribution of volcanic activity localized at both sides of this anomaly. Eastern of the SA, it is possible to recognize a zone with low-velocities beneath the Galan volcano. A sharp limit imposed by high velocities, probably related to metamorphic rocks from the Paleozoic basement (Tacuil and Luracatao ranges) can be detected on the east of the profile. A high-velocity block with seismic activity is located in the crust beneath the Salar de Antofalla (SA) and interpreted as part of the old and cold Palaeozoic magmatic arc (Faja Eruptiva de la Puna Occidental). This block might be responsible for the distribution of volcanic activity localized at both sides of this anomaly. Beneath the Galan volcano and east of the SA, a zone with low-velocities can be recognized. A sharp limit towards high-velocities can be observed on the east of the profile, probably related to metamorphic rocks from the Palaeozoic basement (Tacuil and Luracatao ranges).
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  • 92
    Publication Date: 2020-02-12
    Language: English
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  • 93
    Publication Date: 2022-02-18
    Description: The history of petroleum exploration in central Australia has been enlivened by vigorous debate about the source(s) of the oil and condensate found in the Cooper/Eromanga basin couplet. While early workers quickly recognized the source potential of thick Permian coal seams in the Patchawarra and Toolachee Formations, it took some time for the Jurassic Birkhead Formation and the Cretaceous Murta Formation to become accepted as effective source rocks. Although initially an exploration target, the Cambrian sediments of the underlying Warburton Basin subsequently were never seriously considered to have participated in the oil play, possibly due to a lack of subsurface information as a consequence of limited penetration by only a few widely spaced wells. Dismissal of the Warburton sequence as a source of hydrocarbons was based on its low generative potential as measured by total organic carbon (TOC) and Rock-Eval pyrolysis analyses. As most of the core samples analysed came from the upper part of the basin succession that has been subjected to severe weathering and oxidation, these results might not reflect the true nature of the Warburton Basin’s source rocks. We analysed a suite of source rock extracts, DST oils and sequentially extracted reservoir bitumens from the Gidgealpa field for conventional hydrocarbon biomarkers as well as nitrogen-containing carbazoles. The resulting data show that organic facies is the main control on the distribution of alkylated carbazoles in source rock extracts, oils and sequentially extracted bitumens. The distribution pattern of alkylcarbazoles allows to distinguish between rocks of Jurassic, Permian and pre-Permian age, thereby exceeding the specificity of hydrocarbon biomarkers. While no pre-Permian signature can be found in the DST oils, it is present in sequentially extracted residual oils. However, the pre-Permian molecular source signal is diluted beyond recognition during conventional extraction procedures. The bitumens that are characterised by a pre-Permian geochemical signature derive from differing pore-filling oil pulses and exhibit calculated maturities of up to 1.6% Rc, thereby proving for the first time the petroleum generative capability of source rocks in the Warburton Basin.
    Language: English
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  • 94
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    GFZ German Research Centre for Geosciences
    Publication Date: 2022-03-28
    Description: The IPOC seismic network is part of the Integrated Plate boundary Observatory Chile (IPOC), a European-Chilean network of institutions and scientists organizing and operating a distributed system of instruments and projects dedicated to the study of earthquakes and deformation at the continental margin of Chile. In particular, the seismic network is jointly operated by the GFZ German Research Centre for Geosciences, Potsdam, Germany; the Institut de Physique du Globe Paris, France (IPGP); the Chilean National Seismological Centre (CSN); the Universidad de Chile, Santiago, Chile (UdC); and the Universidad Católica del Norte, Antofagasta, Chile (UCNA). The subduction plate boundary between the South American and the oceanic Nazca plates exhibits some of the largest earthquakes on Earth. The IPOC goal is to improve the understanding of both the physical mechanisms underlying these processes and the natural hazards induced by them. The observatory is designed to monitor the plate boundary system from the Peru-Chile border to south of the city of Antofagasta, from the coast to the high Andes, capturing both great and small earthquakes in this region. A key component of IPOC is its multi-parameter observatories, where at each site a suite of different physical parameters are measured continuously. So far about 20 such multi-parameter stations are installed. All of these sites are equipped with STS-2 broadband seismometers and accelerometers. Additional instrumentation at some of the stations includes continuous GPS, electric and magnetic field (MT), surface inclination, and climate (temperature, air pressure, humidity). Most sites transmit their data in near-real time using a suite of communication channels (VSAT, WiFi, telemetry etc.). Seismic instruments are deployed on concrete pedestals in bedrock caverns (a few meters deep) to measure ground shaking from earthquakes or other sources that last from a tiny fraction of a second to several hours. Strong-motion sensors are deployed next to the broadband sensors to increase the dynamic range and for earthquake engineering applications. Broadband data are freely distributed in real-time and archive data is also available. This DOI encompasses all IPOC seismic data; data is available under FDSN network code CX.
    Language: English
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  • 95
    Publication Date: 2020-02-12
    Language: English
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  • 96
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    Koordinationsstelle Risikomanagement extremer Hochwasser, GeoForschungsZentrum Potsdam
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Language: German , English
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  • 97
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    In:  River flow 2006 : proceedings of the International Conference on Fluvial Hydraulics, Lisbon, Portugal, 6 - 8 September 2006
    Publication Date: 2020-02-12
    Description: Many multipurpose reservoirs are situated in the low mountain range of Germany. Most of them are necessary for drinking water supply and flood protection as well. Other utilizations are recreation, water power and the downstream low water regulation during dry seasons. The operation rules of the reser-voirs have to be optimized to meet the different requirements of use. One tool within this framework is a management system for river basins including all reservoirs and their specific operation rules affecting the downstream reaches. As an optimization objective for instance the minimization of inundation risks can be defined. In this case the risk can be defined as hydraulic and hydrologic safety of the reservoir itself and the risk due to inundation and damaging in the downstream regions. Considering the European Water Framework Directive the ecological aspect of reservoir management is one more point in the optimization process. To es-tablish a pilot project the software TALSIM will be applied to river catchments in the ore mountains (Saxony).
    Language: English
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  • 98
    Publication Date: 2020-02-12
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  • 99
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    In:  Scientific Drilling
    Publication Date: 2020-02-12
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  • 100
    Publication Date: 2020-02-12
    Description: [1] We study the origin of the background seismic noise averaged over long time by cross correlating of the vertical component of motion, which were first normalized by 1-bit coding. We use 1 year of recording at several stations of networks located in North America, western Europe, and Tanzania. We measure normalized amplitudes of Rayleigh waves reconstructed from correlation for all available station to station paths within the networks for positive and negative correlation times to determine the seasonally averaged azimuthal distribution of normalized background energy flow (NBEF) through the networks. We perform the analysis for the two spectral bands corresponding to the primary (10–20 s) and secondary (5–10 s) microseism and also for the 20–40 s band. The direction of the NBEF for the strongest spectral peak between 5 and 10 s is found to be very stable in time with signal mostly coming from the coastline, confirming that the secondary microseism is generated by the nonlinear interaction of the ocean swell with the coast. At the same time, the NBEF in the band of the primary microseism (10–20 s) has a very clear seasonal variability very similar to the behavior of the long-period (20–40 s) noise. This suggests that contrary to the secondary microseism, the primary microseism is not produced by a direct effect of the swell incident on coastlines but rather by the same process that generates the longer-period noise. By simultaneously analyzing networks in California, eastern United States, Europe, and Tanzania we are able to identify main source regions of the 10–20 s noise. They are located in the northern Atlantic and in the northern Pacific during the winter and in the Indian Ocean and in southern Pacific during the summer. These distributions of sources share a great similarity with the map of average ocean wave height map obtained by TOPEX-Poseidon. This suggests that the seismic noise for periods larger than 10 s is clearly related to ocean wave activity in deep water. The mechanism of its generation is likely to be similar to the one proposed for larger periods, namely, infragravity ocean waves.
    Language: English
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