TY - JOUR A1 - Hendriyana, Andri A1 - Bauer, Klaus A1 - Muksin, Umar A1 - Weber, Michael T1 - AIC-based diffraction stacking for local earthquake locations at the Sumatran Fault (Indonesia) JF - Geophysical journal international N2 - We present a new workflow for the localization of seismic events which is based on a diffraction stacking approach. In order to address the effects from complex source radiation patterns, we suggest to compute diffraction stacking from a characteristic function (CF) instead of stacking the original waveform data. A new CF, which is called in the following mAIC (modified from Akaike Information Criterion) is proposed. We demonstrate that both P- and S-wave onsets can be detected accurately. To avoid cross-talk between P and S waves due to inaccurate velocity models, we separate the P and S waves from the mAIC function by making use of polarization attributes. Then, the final image function is represented by the largest eigenvalue as a result of the covariance analysis between P-and S-image functions. Results from synthetic experiments show that the proposed diffraction stacking provides reliable results. The workflow of the diffraction stacking method was finally applied to local earthquake data from Sumatra, Indonesia. Recordings from a temporary network of 42 stations deployed for nine months around the Tarutung pull-apart basin were analysed. The seismic event locations resulting from the diffraction stacking method align along a segment of the Sumatran Fault. A more complex distribution of seismicity is imaged within and around the Tarutung basin. Two lineaments striking N-S were found in the centre of the Tarutung basin which support independent results from structural geology. KW - Time-series analysis KW - Body waves KW - Computational seismology KW - Earthquake source observations KW - Seismicity and tectonics Y1 - 2018 U6 - https://doi.org/10.1093/gji/ggy045 SN - 0956-540X SN - 1365-246X VL - 213 IS - 2 SP - 952 EP - 962 PB - Oxford Univ. Press 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 - 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 - Le Breton, Eline A1 - Handy, Mark R. A1 - Verwater, Vincent F. A1 - Heit, Benjamin A1 - Weber, Michael T1 - Constraints on crustal structure in the vicinity of the adriatic indenter (European Alps) from Vp and Vp/Vs local earthquake tomography JF - Journal of geophysical research : Solid earth N2 - In this study, 3-D models of P-wave velocity (Vp) and P-wave and S-wave ratio (Vp/Vs) of the crust and upper mantle in the Eastern and eastern Southern Alps (northern Italy and southern Austria) were calculated using local earthquake tomography (LET). The data set includes high-quality arrival times from well-constrained hypocenters observed by the dense, temporary seismic networks of the AlpArray AASN and SWATH-D. The resolution of the LET was checked by synthetic tests and analysis of the model resolution matrix. The small inter-station spacing (average of similar to 15 km within the SWATH-D network) allowed us to image crustal structure at unprecedented resolution across a key part of the Alps. The derived P velocity model revealed a highly heterogeneous crustal structure in the target area. One of the main findings is that the lower crust is thickened, forming a bulge at 30-50 km depth just south of and beneath the Periadriatic Fault and the Tauern Window. This indicates that the lower crust decoupled both from its mantle substratum as well as from its upper crust. The Moho, taken to be the iso-velocity contour of Vp = 7.25 km/s, agrees with the Moho depth from previous studies in the European and Adriatic forelands. It is shallower on the Adriatic side than on the European side. This is interpreted to indicate that the European Plate is subducted beneath the Adriatic Plate in the Eastern and eastern Southern Alps. KW - European Alps KW - crustal structure KW - subduction KW - seismic tomography KW - body waves Y1 - 2022 U6 - https://doi.org/10.1029/2021JB023160 SN - 2169-9313 SN - 2169-9356 VL - 127 IS - 2 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Feld, Christian A1 - Mechie, James A1 - Hübscher, Christian A1 - Hall, Jeremy A1 - Nicolaides, Stelios A1 - Gurbuz, Cemil A1 - Bauer, Klaus A1 - Louden, Keith A1 - Weber, Michael T1 - Crustal structure of the eratosthenes seamount, cyprus and S. Turkey from an amphibian wide-angle seismic profile JF - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth N2 - In 2010, project CoCoCo (incipient COntinent-COntinent COllision) recorded a 650 km long amphibian N-S wide-angle seismic profile, extending from the Anatolian plateau across southern Turkey and Cyprus to just south of the Eratosthenes Seamount (ESM). The aim of the project is to reveal the impact of the transition from subduction to continent-continent collision of Africa with Anatolia. Arrival picking, finite-differences ray-tracing and inversion of the offshore and on-offshore data produced a tomographic model across southern Cyprus, the accretionary wedge and the ESM. The main features of this model are (1) crustal P-velocities predominantly lower than 6.5 km/s beneath the ESM, (2) crustal thickness between 28 and 37 km, (3) an upper crustal reflection at 5 km depth beneath the ESM, (4) the likely presence of oceanic crust south of the ESM and a transform margin north of it and (5) a 12 km thick ophiolite sequence on Cyprus. Land shots on Turkey, also recorded on Cyprus, gravity data and geological and previous seismic investigations allow to derive a layered velocity model beneath Anatolia and the northern part of Cyprus. The main features of this model are (1) Moho depths of 38–45 km beneath the Anatolian plateau, (2) an upper and lower crust with large lateral changes in velocity and thickness, (3) a north-dipping subducting plate below Cyprus with a steepening of the dip-angle of the plate at about 45 km depth. Thus, the wide-angle seismic and gravity data provide detailed insights into the 2-D geometry and velocity structures associated with the Cyprus Arc collision zone. Finally, integrated analysis of the geophysics and geology allows a comprehensive interpretation of the crustal structure related to the collision process. KW - Controlled source seismology KW - Subduction zone processes KW - Continental margins: convergent KW - Crustal structure KW - Europe KW - Gravity anomalies and Earth structure Y1 - 2017 U6 - https://doi.org/10.1016/j.tecto.2017.02.003 SN - 0040-1951 SN - 1879-3266 VL - 700 SP - 32 EP - 59 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Giling, Darren P. A1 - Staehr, Peter A. A1 - Grossart, Hans-Peter A1 - Andersen, Mikkel Rene A1 - Boehrer, Bertram A1 - Escot, Carmelo A1 - Evrendilek, Fatih A1 - Gomez-Gener, Lluis A1 - Honti, Mark A1 - Jones, Ian D. A1 - Karakaya, Nusret A1 - Laas, Alo A1 - Moreno-Ostos, Enrique A1 - Rinke, Karsten A1 - Scharfenberger, Ulrike A1 - Schmidt, Silke R. A1 - Weber, Michael A1 - Woolway, R. Iestyn A1 - Zwart, Jacob A. A1 - Obrador, Biel T1 - Delving deeper: Metabolic processes in the metalimnion of stratified lakes JF - Limnology and oceanography N2 - Many lakes exhibit seasonal stratification, during which they develop strong thermal and chemical gradients. An expansion of depth-integrated monitoring programs has provided insight into the importance of organic carbon processing that occurs below the upper mixed layer. However, the chemical and physical drivers of metabolism and metabolic coupling remain unresolved, especially in the metalimnion. In this depth zone, sharp gradients in key resources such as light and temperature co-occur with dynamic physical conditions that influence metabolic processes directly and simultaneously hamper the accurate tracing of biological activity. We evaluated the drivers of metalimnetic metabolism and its associated uncertainty across 10 stratified lakes in Europe and North America. We hypothesized that the metalimnion would contribute highly to whole-lake functioning in clear oligotrophic lakes, and that metabolic rates would be highly variable in unstable polymictic lakes. Depth-integrated rates of gross primary production (GPP) and ecosystem respiration (ER) were modelled from diel dissolved oxygen curves using a Bayesian approach. Metabolic estimates were more uncertain below the epilimnion, but uncertainty was not consistently related to lake morphology or mixing regime. Metalimnetic rates exhibited high day-to-day variability in all trophic states, with the metalimnetic contribution to daily whole-lake GPP and ER ranging from 0% to 87% and < 1% to 92%, respectively. Nonetheless, the metalimnion of low-nutrient lakes contributed strongly to whole-lake metabolism on average, driven by a collinear combination of highlight, low surface-water phosphorous concentration and high metalimnetic volume. Consequently, a single-sensor approach does not necessarily reflect whole-ecosystem carbon dynamics in stratified lakes. Y1 - 2017 U6 - https://doi.org/10.1002/lno.10504 SN - 0024-3590 SN - 1939-5590 VL - 62 SP - 1288 EP - 1306 PB - Wiley CY - Hoboken 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 - Jousset, Philippe A1 - Reinsch, Thomas A1 - Ryberg, Trond A1 - Blanck, Hanna A1 - Clarke, Andy A1 - Aghayev, Rufat A1 - Hersir, Gylfi P. A1 - Henninges, Jan A1 - Weber, Michael A1 - Krawczyk, Charlotte M. T1 - Dynamic strain determination using fibre-optic cables allows imaging of seismological and structural features JF - Nature Communications N2 - Natural hazard prediction and efficient crust exploration require dense seismic observations both in time and space. Seismological techniques provide ground-motion data, whose accuracy depends on sensor characteristics and spatial distribution. Here we demonstrate that dynamic strain determination is possible with conventional fibre-optic cables deployed for telecommunication. Extending recently distributed acoustic sensing (DAS) studies, we present high resolution spatially un-aliased broadband strain data. We recorded seismic signals from natural and man-made sources with 4-m spacing along a 15-km-long fibre-optic cable layout on Reykjanes Peninsula, SW-Iceland. We identify with unprecedented resolution structural features such as normal faults and volcanic dykes in the Reykjanes Oblique Rift, allowing us to infer new dynamic fault processes. Conventional seismometer recordings, acquired simultaneously, validate the spectral amplitude DAS response between 0.1 and 100 Hz bandwidth. We suggest that the networks of fibre-optic telecommunication lines worldwide could be used as seismometers opening a new window for Earth hazard assessment and exploration. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-04860-y SN - 2041-1723 VL - 9 PB - Nature Publ. Group CY - London ER - TY - GEN A1 - Jousset, Philippe A1 - Reinsch, Thomas A1 - Ryberg, Trond A1 - Blanck, Hanna A1 - Clarke, Andy A1 - Aghayev, Rufat A1 - Hersir, Gylfi P. A1 - Henninges, Jan A1 - Weber, Michael A1 - Krawczyk, Charlotte M. T1 - Dynamic strain determination using fibre-optic cables allows imaging of seismological and structural features T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - Natural hazard prediction and efficient crust exploration require dense seismic observations both in time and space. Seismological techniques provide ground-motion data, whose accuracy depends on sensor characteristics and spatial distribution. Here we demonstrate that dynamic strain determination is possible with conventional fibre-optic cables deployed for telecommunication. Extending recently distributed acoustic sensing (DAS) studies, we present high resolution spatially un-aliased broadband strain data. We recorded seismic signals from natural and man-made sources with 4-m spacing along a 15-km-long fibre-optic cable layout on Reykjanes Peninsula, SW-Iceland. We identify with unprecedented resolution structural features such as normal faults and volcanic dykes in the Reykjanes Oblique Rift, allowing us to infer new dynamic fault processes. Conventional seismometer recordings, acquired simultaneously, validate the spectral amplitude DAS response between 0.1 and 100 Hz bandwidth. We suggest that the networks of fibre-optic telecommunication lines worldwide could be used as seismometers opening a new window for Earth hazard assessment and exploration. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 691 KW - North-America KW - fault zone KW - tomography KW - frequency Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-426770 IS - 691 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 -