TY - JOUR A1 - Rein, Theresa A1 - Hannemann, Katrin A1 - Thomas, Christine A1 - Korn, Michael T1 - Location and characteristics of the X-discontinuity beneath SW Morocco and the adjacent shelf area using P-wave receiver functions JF - Geophysical journal international N2 - Receiver function approaches have proven to be valuable for the investigation of crustal and upper mantle discontinuities whose sharp changes in seismic velocities cause wave conversions. While the crustal and mantle transition zone discontinuities are largely understood, the X-discontinuity at 250-350 km depth is still an object of controversial debate. The origin and global distribution of this structure with a velocity jump of 1.5-4.8% for compressional and shear waves is still unexplained. Although the crustal and mantle transition zone discontinuities beneath SW Morocco and surroundings have been investigated, only a few studies observed the X-discontinuity and place the depth at 260-370 km beneath the region of western Morocco. In order to better locate and characterize the X-discontinuity beneath southwest Morocco, we create P-wave receiver functions using data recorded by the Morocco-Munster array and detect the X-discontinuity at apparent depths of 285-350 km. In the western part of our study region we find apparent depths of similar to 310-340 km. The eastern part of the study area appears more complex: we locate two velocity jumps at apparent depths of around 285-295 km and 330-350 km in the northeast, and in the southeast we find a discontinuity at apparent depths of 340-350 km. Due to the large depth range and the twofold appearance of the X-discontinuity, we suggest that two different phase transitions cause the X-discontinuity beneath SW Morocco. The velocity contrasts at larger depths likely point to the coesite-stishovite phase transition occurring in deep eclogitic pools. The shallower depths can be explained by the transition from orthoenstatite to high-pressure clinoenstatite which requires the reaction between eclogite and peridotite to form orthopyroxene-rich peridotite. This reaction is likely related to previously proposed small-scale mantle upwellings beneath SW Morocco. Since both phase transitions require eclogite occurrence, the location of the X-discontinuity in this region can be used to indicate the location of recycled oceanic crust. KW - body waves KW - mantle discontinuities KW - NW Morocco KW - P-waves Y1 - 2020 U6 - https://doi.org/10.1093/gji/ggaa379 SN - 0956-540X SN - 1365-246X VL - 223 IS - 3 SP - 1780 EP - 1793 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Hetenyi, Gyorgy A1 - Molinari, Irene A1 - Clinton, John A1 - Bokelmann, Gotz A1 - Bondar, Istvan A1 - Crawford, Wayne C. A1 - Dessa, Jean-Xavier A1 - Doubre, Cecile A1 - Friederich, Wolfgang A1 - Fuchs, Florian A1 - Giardini, Domenico A1 - Graczer, Zoltan A1 - Handy, Mark R. A1 - Herak, Marijan A1 - Jia, Yan A1 - Kissling, Edi A1 - Kopp, Heidrun A1 - Korn, Michael A1 - Margheriti, Lucia A1 - Meier, Thomas A1 - Mucciarelli, Marco A1 - Paul, Anne A1 - Pesaresi, Damiano A1 - Piromallo, Claudia A1 - Plenefisch, Thomas A1 - Plomerova, Jaroslava A1 - Ritter, Joachim A1 - Rumpker, Georg A1 - Sipka, Vesna A1 - Spallarossa, Daniele A1 - Thomas, Christine A1 - Tilmann, Frederik A1 - Wassermann, Joachim A1 - Weber, Michael A1 - Weber, Zoltan A1 - Wesztergom, Viktor A1 - Zivcic, Mladen A1 - Abreu, Rafael A1 - Allegretti, Ivo A1 - Apoloner, Maria-Theresia A1 - Aubert, Coralie A1 - Besancon, Simon A1 - de Berc, Maxime Bes A1 - Brunel, Didier A1 - Capello, Marco A1 - Carman, Martina A1 - Cavaliere, Adriano A1 - Cheze, Jerome A1 - Chiarabba, Claudio A1 - Cougoulat, Glenn A1 - Cristiano, Luigia A1 - Czifra, Tibor A1 - Danesi, Stefania A1 - Daniel, Romuald A1 - Dannowski, Anke A1 - Dasovic, Iva A1 - Deschamps, Anne A1 - Egdorf, Sven A1 - Fiket, Tomislav A1 - Fischer, Kasper A1 - Funke, Sigward A1 - Govoni, Aladino A1 - Groschl, Gidera A1 - Heimers, Stefan A1 - Heit, Ben A1 - Herak, Davorka A1 - Huber, Johann A1 - Jaric, Dejan A1 - Jedlicka, Petr A1 - Jund, Helene A1 - Klingen, Stefan A1 - Klotz, Bernhard A1 - Kolinsky, Petr A1 - Kotek, Josef A1 - Kuhne, Lothar A1 - Kuk, Kreso A1 - Lange, Dietrich A1 - Loos, Jurgen A1 - Lovati, Sara A1 - Malengros, Deny A1 - Maron, Christophe A1 - Martin, Xavier A1 - Massa, Marco A1 - Mazzarini, Francesco A1 - Metral, Laurent A1 - Moretti, Milena A1 - Munzarova, Helena A1 - Nardi, Anna A1 - Pahor, Jurij A1 - Pequegnat, Catherine A1 - Petersen, Florian A1 - Piccinini, Davide A1 - Pondrelli, Silvia A1 - Prevolnik, Snjezan A1 - Racine, Roman A1 - Regnier, Marc A1 - Reiss, Miriam A1 - Salimbeni, Simone A1 - Santulin, Marco A1 - Scherer, Werner A1 - Schippkus, Sven A1 - Schulte-Kortnack, Detlef A1 - Solarino, Stefano A1 - Spieker, Kathrin A1 - Stipcevic, Josip A1 - Strollo, Angelo A1 - Sule, Balint A1 - Szanyi, Gyongyver A1 - Szucs, Eszter A1 - Thorwart, Martin A1 - Ueding, Stefan A1 - Vallocchia, Massimiliano A1 - Vecsey, Ludek A1 - Voigt, Rene A1 - Weidle, Christian A1 - Weyland, Gauthier A1 - Wiemer, Stefan A1 - Wolf, Felix A1 - Wolyniec, David A1 - Zieke, Thomas T1 - The AlpArray seismic network BT - a large-scale european experiment to image the alpine orogen JF - Surveys in Geophysics N2 - The AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and asthenosphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth. KW - Seismology KW - Alps KW - Seismic network KW - Geodynamics KW - Seismic imaging KW - Mountain building Y1 - 2018 U6 - https://doi.org/10.1007/s10712-018-9472-4 SN - 0169-3298 SN - 1573-0956 VL - 39 IS - 5 SP - 1009 EP - 1033 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Gassner, Alexandra A1 - Thomas, Christine A1 - Krüger, Frank A1 - Weber, Michael H. T1 - Probing the core-mantle boundary beneath Europe and Western Eurasia: A detailed study using PcP JF - Physics of the earth and planetary interiors N2 - We use PcP (the core reflected P phase) recordings of deep earthquakes and nuclear explosions from the Grafenberg (Germany) and NORSAR (Norway) arrays to investigate the core-mantle boundary region beneath Europe and western Eurasia. We find evidence for a previously unknown ultra-low velocity zone 600 km south-east of Moscow, located at the edge of a middle-size low shear- velocity region imaged in seismic tomography that is located beneath the Volga river region. The observed amplitude variations of PcP can be modelled by velocity reductions of P and S-waves of -5% and -15%, respectively, with a density increase of +15%. Travel time delays of pre-and postcursors are indicating a thickness of about 13 km for this ultra-low velocity region (ULVZ). However, our modelling also reveals highly ambiguous amplitude variations of PcP and a reflection off the top of the anomaly for various ULVZs and topography models. Accordingly, large velocity contrasts of up to -10% in V-P and -20% in Vs cannot be excluded. In general, the whole Volga river region shows a complex pattern of PcP amplitudes caused most likely by CMB undulations. Further PcP probes beneath Paris, Kiev and northern Italy indicate likely normal CMB conditions, whereas the samples below Finland and the Hungary-Slovakia border yield strongly amplified PcP signals suggesting strong CMB topography effects. We evaluate the amplitude behaviour of PcP as a function of distance and several ULVZ models using the 1D reflectivity and the 2D Gauss beam method. The influence of the velocity and density perturbations is analysed as well as the anomaly thickness, the dominant period of the source wavelet and interface topographies. Strong variation of the PcP amplitude are obtained as a function of distance and of the impedance contrast. We also consider two types of topographies: undulations atop the CMB in the presence of flat ULVZs and vice versa. Where a broad range of CMB topography dimensions lead to large PcP amplitude variations, only large ULVZ undulations generate significant amplitude scattering. Consequently, this indicates that topography effects of anomalies may mask the true medium parameters as well as the ULVZ thickness. Moreover, there might be a possibility of misinterpreting the precursor as PcP, in particular for thin ULVZs. (C) 2015 Elsevier B.V. All rights reserved. KW - Core-mantle boundary KW - Ultra-low velocity zones KW - Seismology KW - Amplitude and waveform analysis of PcP KW - Earthquakes KW - Nuclear explosions Y1 - 2015 U6 - https://doi.org/10.1016/j.pepi.2015.06.007 SN - 0031-9201 SN - 1872-7395 VL - 246 SP - 9 EP - 24 PB - Elsevier CY - Amsterdam ER -