TY - JOUR A1 - Zang, Arno A1 - Stephansson, Ove A1 - Stenberg, Leif A1 - Plenkers, Katrin A1 - von Specht, Sebastian A1 - Milkereit, Claus A1 - Schill, Eva A1 - Kwiatek, Grzegorz A1 - Dresen, Georg A1 - Zimmermann, Günter A1 - Dahm, Torsten A1 - Weber, Michael T1 - Hydraulic fracture monitoring in hard rock at 410 m depth with an advanced fluid-injection protocol and extensive sensor array JF - Geophysical journal international N2 - In this paper, an underground experiment at the Aspo Hard Rock Laboratory (HRL) is described. Main goal is optimizing geothermal heat exchange in crystalline rock mass at depth by multistage hydraulic fracturing with minimal impact on the environment, that is, seismic events. For this, three arrays with acoustic emission, microseismicity and electromagnetic sensors are installed mapping hydraulic fracture initiation and growth. Fractures are driven by three different water injection schemes (continuous, progressive and pulse pressurization). After a brief review of hydraulic fracture operations in crystalline rock mass at mine scale, the site geology and the stress conditions at Aspo HRL are described. Then, the continuous, single-flow rate and alternative, multiple-flow rate fracture breakdown tests in a horizontal borehole at depth level 410 m are described together with the monitoring networks and sensitivity. Monitoring results include the primary catalogue of acoustic emission hypocentres obtained from four hydraulic fractures with the in situ trigger and localizing network. The continuous versus alternative water injection schemes are discussed in terms of the fracture breakdown pressure, the fracture pattern from impression packer result and the monitoring at the arrays. An example of multistage hydraulic fracturing with several phases of opening and closing of fracture walls is evaluated using data from acoustic emissions, seismic broad-band recordings and electromagnetic signal response. Based on our limited amount of in situ tests (six) and evaluation of three tests in Avro granodiorite, in the multiple-flow rate test with progressively increasing target pressure, the acoustic emission activity starts at a later stage in the fracturing process compared to the conventional fracturing case with continuous water injection. In tendency, also the total number and magnitude of acoustic events are found to be smaller in the progressive treatment with frequent phases of depressurization. KW - Geomechanics KW - Fracture and flow KW - Broad-band seismometers Y1 - 2016 SN - 0956-540X SN - 1365-246X VL - 208 SP - 790 EP - 813 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Weber, Michael A1 - Scholz, Denis A1 - Schröder-Ritzrau, Andrea A1 - Deininger, Michael A1 - Spötl, Christoph A1 - Lugli, Federico A1 - Mertz-Kraus, Regina A1 - Jochum, Klaus Peter A1 - Fohlmeister, Jens Bernd A1 - Stumpf, Cintia F. A1 - Riechelmann, Dana F. C. T1 - Evidence of warm and humid interstadials in central Europe during early MISSUE 3 revealed by a multi-proxy speleothem record JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Marine Isotope Stage 3 (MIS 3, 57-27 ka) was characterised by numerous rapid climate oscillations (i.e., Dansgaard-Oeschger (D/O-) events), which are reflected in various climate archives. So far, MIS 3 speleothem records from central Europe have mainly been restricted to caves located beneath temperate Alpine glaciers or close to the Atlantic Ocean. Thus, MIS 3 seemed to be too cold and dry to enable speleothem growth north of the Alps in central Europe. Here we present a new speleothem record from Bunker Cave, Germany, which shows two distinct growth phases from 52.0 (+0.8, -0.5) to 50.9 (+0.6, -1.3) ka and 473 (+1.0, -0.6) to 42.8 (+/- 0.9) ka, rejecting this hypothesis. These two growth phases potentially correspond to the two warmest and most humid phases in central Europe during MIS 3, which is confirmed by pollen data from the nearby Eifel. The hiatus separating the two phases is associated with Heinrich stadial 5 (HS 5), although the growth stop precedes the onset of HS 5. The first growth phase is characterised by a fast growth rate, and Mg concentrations and Sr isotope data suggest high infiltration and the presence of soil cover above the cave. The second growth phase was characterised by drier, but still favourable conditions for speleothem growth. During this phase, the delta C-13 values show a significant decrease associated with D/O-event 12. The timing of this shift is in agreement with other MIS 3 speleothem data from Europe and Greenland ice core data. (C) 2018 Elsevier Ltd. All rights reserved. KW - Speleothems KW - Pleistocene KW - Palaeoclimatology KW - Europe KW - Dansgaard-Oeschger event KW - Marine isotope stage 3 KW - Bunker cave KW - Multi-proxy approach KW - U-Th series Y1 - 2018 U6 - https://doi.org/10.1016/j.quascirev.2018.09.045 SN - 0277-3791 VL - 200 SP - 276 EP - 286 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Sarrazin, Fanny J. A1 - Kumar, Rohini A1 - Basu, Nandita B. A1 - Musolff, Andreas A1 - Weber, Michael A1 - Van Meter, Kimberly J. A1 - Attinger, Sabine T1 - Characterizing catchment-scale nitrogen legacies and constraining their uncertainties JF - Water resources research N2 - Improving nitrogen (N) status in European water bodies is a pressing issue. N levels depend not only on current but also past N inputs to the landscape, that have accumulated through time in legacy stores (e.g., soil, groundwater). Catchment-scale N models, that are commonly used to investigate in-stream N levels, rarely examine the magnitude and dynamics of legacy components. This study aims to gain a better understanding of the long-term fate of the N inputs and its uncertainties, using a legacy-driven N model (ELEMeNT) in Germany's largest national river basin (Weser; 38,450 km(2)) over the period 1960-2015. We estimate the nine model parameters based on a progressive constraining strategy, to assess the value of different observational data sets. We demonstrate that beyond in-stream N loading, soil N content and in-stream N concentration allow to reduce the equifinality in model parameterizations. We find that more than 50% of the N surplus denitrifies (1480-2210 kg ha(-1)) and the stream export amounts to around 18% (410-640 kg ha(-1)), leaving behind as much as around 230-780 kg ha(-1) of N in the (soil) source zone and 10-105 kg ha(-1) in the subsurface. A sensitivity analysis reveals the importance of different factors affecting the residual uncertainties in simulated N legacies, namely hydrologic travel time, denitrification rates, a coefficient characterizing the protection of organic N in source zone and N surplus input. Our study calls for proper consideration of uncertainties in N legacy characterization, and discusses possible avenues to further reduce the equifinality in water quality modeling. KW - nitrogen legacies KW - water quality modeling KW - equifinality KW - parameter KW - estimation KW - sensitivity analysis Y1 - 2022 U6 - https://doi.org/10.1029/2021WR031587 SN - 0043-1397 SN - 1944-7973 VL - 58 IS - 4 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Ryberg, Trond A1 - Braeuer, Benjamin A1 - Weber, Michael T1 - Upper mantle structure at Walvis Ridge from P-n tomography JF - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth N2 - Passive continental margins offer the unique opportunity to study the processes involved in continental extension and break-up. Within the LISPWAL (Llthospheric Structure of the Namibian continental Passive margin at the intersection with the Walvis Ridge from amphibious seismic investigations) project, combined on- and offshore seismic experiments were designed to characterize the Southern African passive margin at the Walvis Ridge in northern Namibia. In addition to extensive analysis of the crustal structures, we carried out seismic investigations targeting the velocity structure of the upper mantle in the landfall region of the Walvis Ridge with the Namibian coast. Upper mantle P-n travel time tomography from controlled source, amphibious seismic data was used to investigate the sub-Moho upper mantle seismic velocity. We succeeded in imaging upper mantle structures potentially associated with continental break-up and/or the Tristan da Cunha hotspot track. We found mostly coast-parallel sub-Moho velocity anomalies, interpreted as structures which were created during Gondwana break-up. (C)2016 Published by Elsevier B.V. KW - Seismic investigations KW - P-n tomography KW - passive continental margin KW - Gondwana break-up Y1 - 2017 U6 - https://doi.org/10.1016/j.tecto.2016.08.009 SN - 0040-1951 SN - 1879-3266 VL - 716 SP - 121 EP - 129 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Planert, Lars A1 - Behrmann, Jan H. A1 - Jokat, Wilfried A1 - Fromm, Tanja A1 - Ryberg, Trond A1 - Weber, Michael A1 - Haberland, Christian T1 - The wide-angle seismic image of a complex rifted margin, offshore North Namibia: Implications for the tectonics of continental breakup JF - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth N2 - Voluminous magmatism during the South Atlantic opening has been considered as a classical example for plume related continental breakup. We present a study of the crustal structure around Walvis Ridge, near the intersection with the African margin. Two wide-angle seismic profiles were acquired. One is oriented NNW–SSE, following the continent–ocean transition and crossing Walvis Ridge. A second amphibious profile runs NW–SE from the Angola Basin into continental Namibia. At the continent–ocean boundary (COB) the mafic crust beneath Walvis Ridge is up to 33 km thick, with a pronounced high-velocity lower crustal body. Towards the south there is a smooth transition to 20–25 km thick crust underlying the COB in the Walvis Basin, with a similar velocity structure, indicating a gabbroic lower crust with associated cumulates at the base. The northern boundary of Walvis Ridge towards the Angola Basin shows a sudden change to oceanic crust only 4–6 km thick, coincident with the projection of the Florianopolis Fracture Zone, one of the most prominent tectonic features of the South Atlantic ocean basin. In the amphibious profile the COB is defined by a sharp transition from oceanic to rifted continental crust, with a magmatic overprint landward of the intersection of Walvis Ridge with the Namibian margin. The continental crust beneath the Congo Craton is 40 km thick, shoaling to 35 km further SE. The velocity models show that massive high-velocity gabbroic intrusives are restricted to a narrow zone directly underneath Walvis Ridge and the COB in the south. This distribution of rift-related magmatism is not easily reconciled with models of continental breakup following the establishment of a large, axially symmetric plume in the Earth's mantle. Rift-related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism, dividing the margin in a magma-dominated southern and an essentially amagmatic northern segment. KW - Wide-angle seismic KW - Crustal structure KW - Walvis Ridge KW - Hotspot KW - Rifted continental margin KW - South Atlantic Y1 - 2017 U6 - https://doi.org/10.1016/j.tecto.2016.06.024 SN - 0040-1951 SN - 1879-3266 VL - 716 SP - 130 EP - 148 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Mohsen, Ayman A1 - Kind, Rainer A1 - Sobolev, Stephan Vladimir A1 - Weber, Michael T1 - Thickness of the lithosphere east of the Dead Sea Transform JF - Geophysical journal international N2 - We use the S receiver function method to study the lithosphere at the Dead Sea Transform (DST). A temporary network of 22 seismic broad-band stations was operated on both sides of the DST from 2000 to 2001 as part of the DESERT project. We also used data from six additional permanent broad-band seismic stations at the DST and in the surrounding area, that is, in Turkey, Saudi Arabia, Egypt and Cyprus. Clear S-to-P converted phases from the crust-mantle boundary (Moho) and a deeper discontinuity, which we interpret as lithosphere-asthenosphere boundary (LAB) have been observed. The Moho depth (30-38 km) obtained from S receiver functions agrees well with the results from P receiver functions and other geophysical data. We observe thinning of the lithosphere on the eastern side of the DST from 80 km in the north of the Dead Sea to about 65 km at the Gulf of Aqaba. On the western side of the DST, the few data indicate a thin LAB of about 65 km. For comparison, we found a 90-km-thick lithosphere in eastern Turkey and a 160-km-thick lithosphere under the Arabian shield, respectively. These observations support previous suggestions, based on xenolith data, heat flow observations, regional uplift history and geodynamic modelling, that the lithosphere around DST has been significantly thinned in the Late Cenozoic, likely following rifting and spreading of the Red Sea. KW - Dead Sea Transform KW - S receiver functions KW - thickness of the lithosphere Y1 - 2006 U6 - https://doi.org/10.1111/j.1365-246X.2006.03185.x SN - 0956-540X SN - 1365-246X VL - 167 IS - 2 SP - 845 EP - 852 PB - Blackwell CY - Oxford ER - TY - JOUR A1 - Mallonn, Matthias A1 - Poppenhäger, Katja A1 - Granzer, Thomas A1 - Weber, Michael A1 - Strassmeier, Klaus G. T1 - Detection capability of ground-based meter-sized telescopes for shallow exoplanet transits JF - Astronomy and astrophysics : an international weekly journal N2 - Meter-sized ground-based telescopes are frequently used today for the follow-up of extrasolar planet candidates. While the transit signal of a Jupiter-sized object can typically be detected to a high level of confidence with small telescope apertures as well, the shallow transit dips of planets with the size of Neptune and smaller are more challenging to reveal. We employ new observational data to illustrate the photometric follow-up capabilities of meter-sized telescopes for shallow exoplanet transits. We describe in detail the capability of distinguishing the photometric signal of an exoplanet transit from an underlying trend in the light curve. The transit depths of the six targets we observed, Kepler-94b, Kepler-63b, K2-100b, K2-138b, K2-138c, and K2-138e, range from 3.9 ppt down to 0.3 ppt. For five targets of this sample, we provide the first ground-based photometric follow-up. The timing of three targets is precisely known from previous observations, and the timing of the other three targets is uncertain and we aim to constrain it. We detect or rule out the transit features significantly in single observations for the targets that show transits of 1.3 ppt or deeper. The shallower transit depths of two targets of 0.6 and 0.8 ppt were detected tentatively in single light curves, and were detected significantly by repeated observations. Only for the target of the shallowest transit depth of 0.3 ppt were we unable to draw a significant conclusion despite combining five individual light curves. An injection-recovery test on our real data shows that we detect transits of 1.3 ppt depth significantly in single light curves if the transit is fully covered, including out-of-transit data toward both sides, in some cases down to 0.7 ppt depth. For Kepler-94b, Kepler-63b, and K2-100b, we were able to verify the ephemeris. In the case of K2-138c with a 0.6 ppt deep transit, we were able to refine it, and in the case of K2-138e, we ruled out the transit in the time interval of more than ±1.5 σ of its current literature ephemeris. KW - methods: observational KW - techniques: photometric KW - planets and satellites: fundamental parameters Y1 - 2022 U6 - https://doi.org/10.1051/0004-6361/202140599 SN - 0004-6361 SN - 1432-0746 VL - 657 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Kottmeier, Christoph A1 - Agnon, Amotz A1 - Al-Halbouni, Djamil A1 - Alpert, Pinhas A1 - Corsmeier, Ulrich A1 - Dahm, Torsten A1 - Eshel, Adam A1 - Geyer, Stefan A1 - Haas, Michael A1 - Holohan, Eoghan A1 - Kalthoff, Norbert A1 - Kishcha, Pavel A1 - Krawczyk, Charlotte A1 - Lati, Joseph A1 - Laronne, Jonathan B. A1 - Lott, Friederike A1 - Mallast, Ulf A1 - Merz, Ralf A1 - Metzger, Jutta A1 - Mohsen, Ayman A1 - Morin, Efrat A1 - Nied, Manuela A1 - Roediger, Tino A1 - Salameh, Elias A1 - Sawarieh, Ali A1 - Shannak, Benbella A1 - Siebert, Christian A1 - Weber, Michael T1 - New perspectives on interdisciplinary earth science at the Dead Sea: The DESERVE project JF - The science of the total environment : an international journal for scientific research into the environment and its relationship with man N2 - The Dead Sea region has faced substantial environmental challenges in recent decades, including water resource scarcity, similar to 1 m annual decreases in the water level, sinkhole development, ascending-brine freshwater pollution, and seismic disturbance risks. Natural processes are significantly affected by human interference as well as by climate change and tectonic developments over the long term. To get a deep understanding of processes and their interactions, innovative scientific approaches that integrate disciplinary research and education are required. The research project DESERVE (Helmholtz Virtual Institute Dead Sea Research Venue) addresses these challenges in an interdisciplinary approach that includes geophysics, hydrology, and meteorology. The project is implemented by a consortium of scientific institutions in neighboring countries of the Dead Sea (Israel, Jordan, Palestine Territories) and participating German Helmholtz Centres (KIT, GFZ, UFZ). A new monitoring network of meteorological, hydrological, and seismic/geodynamic stations has been established, and extensive field research and numerical simulations have been undertaken. For the first time, innovative measurement and modeling techniques have been applied to the extreme conditions of the Dead Sea and its surroundings. The preliminary results show the potential of these methods. First time ever performed eddy covariance measurements give insight into the governing factors of Dead Sea evaporation. High-resolution bathymetric investigations reveal a strong correlation between submarine springs and neo-tectonic patterns. Based on detailed studies of stratigraphy and borehole information, the extension of the subsurface drainage basin of the Dead Sea is now reliably estimated. Originality has been achieved in monitoring flash floods in an arid basin at its outlet and simultaneously in tributaries, supplemented by spatio-temporal rainfall data. Low-altitude, high resolution photogrammetry, allied to satellite image analysis and to geophysical surveys (e.g. shear-wave reflections) has enabled a more detailed characterization of sinkhole morphology and temporal development and the possible subsurface controls thereon. All the above listed efforts and scientific results take place with the interdisciplinary education of young scientists. They are invited to attend joint thematic workshops and winter schools as well as to participate in field experiments. (C) 2015 The Authors. Published by Elsevier B.V. KW - Climate KW - Water balance KW - Flash floods KW - Seismicity KW - Sinkholes KW - Education Y1 - 2016 U6 - https://doi.org/10.1016/j.scitotenv.2015.12.003 SN - 0048-9697 SN - 1879-1026 VL - 544 SP - 1045 EP - 1058 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kastle, Emanuel D. A1 - Weber, Michael A1 - Krüger, Frank T1 - Complex Deep Structure of the African Low-Velocity Zone JF - Bulletin of the Seismological Society of America N2 - We use recently deployed seismological arrays in Africa to sample a 2D cross section through the mantle down to the core-mantle boundary (CMB). By making use of travel-time residuals of S, ScS, and SKS phases, a new shear-velocity model of the African low-velocity zone (ALVZ) is derived. Our model suggests between 1.2% shear-velocity reduction at the top and 5% at the bottom with respect to 1D reference models. The average reduction over the whole low-velocity zone (LVZ) amounts to 2% in the presented model and is therefore about twice as strong as values found in global tomographic models. The top of the LVZ reaches up to 1200-km depth, and its lateral extent at the CMB is about 35 degrees. We propose the existence of a gap of 300 km, splitting the structure into two blocks. Our results are based on remarkable differences in SK(K) S travel-time residuals over a few degrees distance. The complexity of the structure could provide a key to an improved understanding of the deep-mantle LVZ dynamics and composition by comparison to geodynamic models. The gap in the model might suggest that the 2D cross section is cutting through a 3D indentation in the boundary of the ALVZ but may also be interpreted as a sign of two individual plumes, rather than one large homogeneous upwelling. Y1 - 2017 U6 - https://doi.org/10.1785/0120160215 SN - 0037-1106 SN - 1943-3573 VL - 107 SP - 1688 EP - 1703 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Jozi Najafabadi, Azam A1 - Haberland, Christian A1 - Ryberg, Trond A1 - Verwater, Vincent F. A1 - Breton, Eline le A1 - Handy, Mark R. A1 - Weber, Michael T1 - Relocation of earthquakes in the southern and eastern Alps (Austria, Italy) recorded by the dense, temporary SWATH-D network using a Markov chain Monte Carlo inversion JF - Solid earth : SE ; an interaktive open access journal of the European Geosciences Union N2 - In this study, we analyzed a large seismological dataset from temporary and permanent networks in the southern and eastern Alps to establish high-precision hypocenters and 1-D V-P and V-P/V-S models. The waveform data of a subset of local earthquakes with magnitudes in the range of 1-4.2 M-L were recorded by the dense, temporary SWATH-D network and selected stations of the AlpArray network between September 2017 and the end of 2018. The first arrival times of P and S waves of earthquakes are determined by a semi-automatic procedure. We applied a Markov chain Monte Carlo inversion method to simultaneously calculate robust hypocenters, a 1-D velocity model, and station corrections without prior assumptions, such as initial velocity models or earthquake locations. A further advantage of this method is the derivation of the model parameter uncertainties and noise levels of the data. The precision estimates of the localization procedure is checked by inverting a synthetic travel time dataset from a complex 3-D velocity model and by using the real stations and earthquakes geometry. The location accuracy is further investigated by a quarry blast test. The average uncertainties of the locations of the earthquakes are below 500m in their epicenter and similar to 1.7 km in depth. The earthquake distribution reveals seismicity in the upper crust (0-20 km), which is characterized by pronounced clusters along the Alpine frontal thrust, e.g., the Friuli-Venetia (FV) region, the Giudicarie-Lessini (GL) and Schio-Vicenza domains, the Austroalpine nappes, and the Inntal area. Some seismicity also occurs along the Periadriatic Fault. The general pattern of seismicity reflects head-on convergence of the Adriatic indenter with the Alpine orogenic crust. The seismicity in the FV and GL regions is deeper than the modeled frontal thrusts, which we interpret as indication for southward propagation of the southern Alpine deformation front (blind thrusts). Y1 - 2021 U6 - https://doi.org/10.5194/se-12-1087-2021 SN - 1869-9529 VL - 12 IS - 5 SP - 1087 EP - 1109 PB - Copernicus CY - Göttingen ER -