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  • 1
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    Imaging seismic wave-fields with AlpArray and neighboring European networks (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2024-02-28
    Description: The AlpArray experiment and the deployment of Swath-D together with the dense permanent network in Italy allow for detailed imaging of the spatio-temporal imaging complexity of seismic wave-fields within the greater Alpine region. The distance of any point within the area to the nearest station is less than 30 km, resulting in an average inter-station distance of about 45 km. With a much denser deployment in a smaller region of the Alps (320 km in length and 140 km wide), the Swath-D network possesses an average inter-station distance of about 15 km. We show that seismogram sections with a spatial sampling of less than 5 km can be obtained using recordings of these regional arrays for just a single event. Multiply reflected body waves can be observed for up to 2 h after source time. In addition, we provide and describe animations of long-period seismic wave-fields using recordings of about 1300–1600 broadband stations for six representative earthquakes. These illustrate the considerable spatio-temporal variability of the wave-field’s properties at a high lateral resolution. Within denser station distributions like those provided by Swath-D, even shorter period body and surface wave features can be recovered. The decrease of the horizontal wavelength from P to S to surface waves, deviations from spherically symmetric wavefronts, and the capability to detect multi-orbit arrivals are demonstrated qualitatively by the presented wave-field animations, which are a valuable tool for educational, quality control, and research purposes. We note that the information content of the acquired datasets can only be adequately explored by application of appropriate quantitative methods accounting for the considerable complexity of the seismic wave-fields as revealed by the now available station configuration.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Christian-Albrechts-Universität zu Kiel (3094)
    Keywords: ddc:551.22 ; Seismology ; Wave-fields ; Animations ; Alps ; AlpArray ; Swath-D
    Language: English
    Type: doc-type:article
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  • 2
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    Dead Sea Basin Imaged by Ambient Seismic Noise Tomography (2012)
    In:  Pure and Applied Geophysics
    Details
    Publication Date: 2020-02-12
    Description: In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007 to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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  • 3
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    Stress tensor and focal mechanisms in the Dead Sea basin (2016)
    In:  Journal of Seismology
    Details
    Publication Date: 2020-02-12
    Description: We use the recorded seismicity, confined to the Dead Sea basin and its boundaries, by the Dead Sea Integrated Research (DESIRE) portable seismic network and the Israel and Jordan permanent seismic networks for studying the mechanisms of earthquakes in the Dead Sea basin. The observed seismicity in the Dead Sea basin is divided into nine regions according to the spatial distribution of the earthquakes and the known tectonic features. The large number of recording stations and the adequate station distribution allowed the reliable determinations of 494 earthquake focal mechanisms. For each region, based on the inversion of the observed polarities of the earthquakes, we determine the focal mechanisms and the associated stress tensor. For 159 earthquakes, out of the 494 focal mechanisms, we could determine compatible fault planes. On the eastern side, the focal mechanisms are mainly strike-slip mechanism with nodal planes in the N-S and E-W directions. The azimuths of the stress axes are well constrained presenting minimal variability in the inversion of the data, which is in agreement with the Eastern Boundary fault on the east side of the Dead Sea basin and what we had expected from the regional geodynamics. However, larger variabilities of the azimuthal and dip angles are observed on the western side of the basin. Due to the wider range of azimuths of the fault planes, we observe the switching of σ1 and σ2 or the switching of σ2 and σ3 as major horizontal stress directions. This observed switching of stress axes allows having dip-slip and normal mechanisms in a region that is dominated by strike-slip motion.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 4
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    Crustal structure of the Dead Sea Basin (DSB) from a Receiver Function Analysis (2011)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: The Dead Sea Transform (DST) is a major left-lateral strike-slip fault that accommodates the relative motion between the African and Arabian plates, connecting a region of extension in the Red Sea to the Taurus collision zone in Turkey over a length of about 1100 km. The Dead Sea Basin (DSB) is one of the largest basins along the DST. The DSB is a morphotectonic depression along the DST, divided into a northern and a southern sub-basin, separated by the Lisan salt diapir. We report on a receiver function study of the crust within the multidisciplinary geophysical project, DEad Sea Integrated REsearch (DESIRE), to study the crustal structure of the DSB. A temporary seismic network was operated on both sides of the DSB between 2006 October and 2008 April. The aperture of the network is approximately 60 km in the E—W direction crossing the DSB on the Lisan peninsula and about 100 km in the N—S direction. Analysis of receiver functions from the DESIRE temporary network indicates that Moho depths vary between 30 and 38 km beneath the area. These Moho depth estimates are consistent with results of near-vertical incidence and wide-angle controlled-source techniques. Receiver functions reveal an additional discontinuity in the lower crust, but only in the DSB and west of it. This leads to the conclusion that the internal crustal structure east and west of the DSB is different at the present-day. However, if the 107 km left-lateral movement along the DST is taken into account, then the region beneath the DESIRE array where no lower crustal discontinuity is observed would have lain about 18 Ma ago immediately adjacent to the region under the previous DESERT array west of the DST where no lower crustal discontinuity is recognized.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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  • 5
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    Fibre-optic distributed acoustic sensing data from Reykjanes, Iceland (2018)
    GFZ Data Services
    Details
    Publication Date: 2020-02-12
    Description: Imaging the internal structure of faults remains challenging using conventional seismometers. Here, the authors use deployed fibre-optic cables to obtain strain data and identify faults and volcanic dykes in Iceland. Such fibre-optic networks are pervasive for telecommu-nication and could be used for hazard assessment. Natural hazard prediction and efficient crustal exploration requires dense seismic observa-tions both in time and space. Seismological techniques provide ground-motion data, whose accuracy depends on sensor characteristics and spatial distribution. In the manuscript Jousset et al. (2018), we demonstrate that 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.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 6
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    Imaging the deep roots of the San Andreas Fault Zone at Parkfield, CA, with magnetotelluric measurements (2005)
    In:  Protokoll zum 21. Kolloquium „Elektromagnetische Tiefenforschung“
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    Publication Date: 2020-02-12
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 7
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    Local seismicity pattern and 1-D velocity model in the Southern and Eastern Alps using the temporary SWATH-D network data (2019)
    In:  Geophysical Research Abstracts
    Details
    Publication Date: 2021-06-15
    Description: The Alps as the result of the convergence of the African and European plates represent extremely complex struc-tures and kinematics. The Southern and Eastern Alps as part of this continental collision are the target area of thecurrent study. In this region, the Priadriatic Fault is sinistrally offset by the Guidicarie Fault and a switch in the sub-duction polarity had been proposed. In order to better understand the crustal and upper-mantle structure and how itis related to faults seen at the surface, we aim to assess the precise distribution of local earthquakes (potentially in-dicating active faults) and the seismic velocity structure in the subsurface. In our investigation, we use the data of avery dense seismic network deployed in the Southern and Eastern Alps (SWATH-D network - DFG funded priorityProgramme 4D-MB) to provide seismicity pattern and velocity structure of the crust and possibly the upper mantle.This temporary network consists of 150 stations with an average inter-station spacing of 15 km complementingthe larger scale AlpArray Seismic Network (AASN). The objectives are, accordingly, to implement a reliable andfully automated algorithm to detect the events and pick the phase onset times of local earthquakes, provide precisehypocentral locations and calculate a velocity model for the target area. Here we focus on the first results of theearthquake analysis procedure and present a 1-D velocity model for the Southern and Eastern Alps. Later, this datawill be used for a 3-D tomographic inversion. So far, we used 10 months of data from September 2017 to Jun 2018and implemented an automated multi-stage processing chain to provide the first catalog. The catalog comprises123 local earthquakes with 5261 P and 2651 S picks. The hypocentral locations were then calculated and a 1-Dvelocity model was also obtained using simultaneous inversion of hypocenters, velocity, and station corrections.The seismicity pattern is characterized by rather diffuse clusters in the Friuli, Lake Garda, Brenner and Trentinoregions with low to medium magnitude (ML 0-4) events within the upper 25 km of the crust. The central part ofthe region, where the Preadriatice fault sinistrally offset by the Guidicarie Fault and its related fold-and-thrust belt,has obviously less activity. Our 1-D velocity model indicates upper crustal velocities that are higher than averagefor the whole Alpine region.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 8
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    LISPWAL : Lithospheric structure of the Namibian Continental passive margin at the intersection with the Walvis Ridge from amphibious seismic investigations ; November 2010 - January 2011 Namibia (2014)
    Deutsches GeoForschungsZentrum GFZ
    In:  Scientific Technical Report - Data | GIPP Experiment- and Data Archive
    Details
    Publication Date: 2020-02-12
    Description: Passive continental margins offer the unique opportunity to study the processes involved in continental extension and break up as well as the role of hot-spot related magmatism. We conducted combined on- and offshore seismic experiments in Northern Namibia designed to characterize the Southern African passive margin at the interaction with the Walvis Ridge, to assess the interaction of the presumed plume with continental lithosphere and to determine the deep structure of the transition from the coastal fold belt to the stable craton, where the Walvis Ridge hits the African continent. The seismic project integrated three experiments, (A) an onshore, coast-parallel refraction seismic profile, (B) two onshore-offshore wide-angle seismic transects, and (C) a combined on- and offshore seismic experiment to image the sub-Moho velocity (Pn tomography) at the ocean-continent transition (Fig. 1). The knowledge of the lithospheric structure of the margin together with results from other geoscientific studies (e.g., conducted within the SPPSAMPLE, DFG Priority Program 1375, South Atlantic Margin Processes and Links with onshore Evolution) will help to address fundamental questions such as, how continental crust and plume head interact, what the extent and volumes of magmatic underplating is, and how and which inherited (continental) structures might have been involved and utilized in the break-up process.
    Language: English
    Type: info:eu-repo/semantics/report
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  • 9
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    Complex Deep Structure of the African Low‐Velocity Zone (2017)
    In:  Bulletin of the Seismological Society of America
    Details
    Publication Date: 2020-02-12
    Description: 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°. 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.
    Language: English
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  • 10
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    Exploring Structural Controls on Sumatran Earthquakes (2010)
    In:  Eos, Transactions American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Description: A series of linked marine and land studies have recently targeted the Sumatra subduction zone, focusing on the 2004 and 2005 plate boundary earthquake ruptures in Indonesia. A collaborative research effort by scientists from the United Kingdom (UK Sumatra Consortium), Indonesia, United States, France, and Germany is focusing on imaging the crustal structure of the margin to examine controls on along-strike and updip earthquake rupture propagation. The fundamental science objective is to examine how margin architecture and properties control earthquake rupture location and propagation.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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