22 research outputs found

    Implications of 3D Seismic Raytracing on Focal Mechanism Determination

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    The purpose of this study is to investigate apparent first‐motion polarities mismatch at teleseismic distances in the determination of focal mechanism. We implement and compare four seismic raytracing algorithms to compute ray paths and travel times in 1D and 3D velocity models. We use the raytracing algorithms to calculate the takeoff angles from the hypocenter of the 24 August 2016 Mw 6.8 Chauk earthquake (depth 90 km) in central Myanmar to the stations BFO, GRFO, KONO, and ESK in Europe using a 3D velocity model of the upper mantle below Asia. The differences in the azimuthal angles calculated in the 1D and 3D velocity models are considerable and have a maximum value of 19.6°. Using the takeoff angles for the 3D velocity model, we are able to resolve an apparent polarity mismatch where these stations move from the dilatational to the compressional quadrant. The polarities of synthetic waveforms change accordingly when we take the takeoff angles corresponding to the 3D model into account. This method has the potential to improve the focal mechanism solutions, especially for historical earthquakes where limited waveform data are available.acceptedVersio

    Fifteen-year follow-up of quality of life in type 1 diabetes mellitus

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    AIM: To evaluate metabolic control and health-related quality of life (HRQOL) in a type 1 diabetes mellitus (T1DM) population. METHODS: As part of a prospective cohort study, 283 T1DM patients treated with various insulin treatment modalities including multiple daily injections (MDI) and continuous subcutaneous insulin infusion (CSII) were examined annually. HRQOL was measured using the SF-36 and EuroQol questionnaires. Data regarding HRQOL, glycaemic and metabolic control from baseline and follow-up measures in 2002 and 2010 were analysed. Linear mixed models were used to calculate estimated values and differences between the three moments in time and the three treatment modalities. RESULTS: Significant changes [mean Δ (95%CI)] in body mass index [2.4 kg/m(2) (1.0, 3.8)], systolic blood pressure [-6.4 mmHg (-11.4, -1.3)] and EuroQol-VAS [-7.3 (-11.4, -3.3)] were observed over time. In 2010, 168 patients were lost to follow-up. Regarding mode of therapy, 52 patients remained on MDI, 28 remained on CSII, and 33 patients switched from MDI to CSII during follow-up. Among patients on MDI, HRQOL decreased significantly over time: mental component summary [-9.8 (-16.3, -3.2)], physical component summary [-8.6 (-15.3, -1.8)] and EuroQol-VAS [-8.1 (-14.0, -2.3)], P < 0.05 for all. For patients using CSII, the EuroQol-VAS decreased [-9.6 (-17.5, -1.7)]. None of the changes over time in HRQOL differed significantly with the changes over time within the other treatment groups. CONCLUSION: No differences with respect to metabolic and HRQOL parameters between the various insulin treatment modalities were observed after 15 years of follow-up in T1DM patients

    The European Plate Observing System and the Arctic

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    The European Plate Observing System (EPOS) aims to integrate existing infrastructures in the solid earth sciences into a single infrastructure, enabling earth scientists across Europe to combine, model, and interpret multidisciplinary datasets at different time and length scales. In particular, a primary objective is to integrate existing research infrastructures within the fields of seismology, geodesy, geophysics, geology, rock physics, and volcanology at a pan-European level. The added value of such integration is not visible through individual analyses of data from each research infrastructure; it needs to be understood in a long-term perspective that includes the time when changes implied by current scientific research results are fully realized and their societal impacts have become clear. EPOS is now entering its implementation phase following a four-year preparatory phase during which 18 member countries in Europe contributed more than 250 research infrastructures to the building of this pan-European vision. The Arctic covers a significant portion of the European plate and therefore plays an important part in research on the solid earth in Europe. However, the work environment in the Arctic is challenging. First, most of the European Plate boundary in the Arctic is offshore, and hence, sub-sea networks must be built for solid earth observation. Second, ice covers the Arctic Ocean where the European Plate boundary crosses through the Gakkel Ridge, so innovative technologies are needed to monitor solid earth deformation. Therefore, research collaboration with other disciplines such as physical oceanography, marine acoustics, and geo-biology is necessary. The establishment of efficient research infrastructures suitable for these challenging conditions is essential both to reduce costs and to stimulate multidisciplinary research.Le systĂšme European Plate Observing System (EPOS) vise l’intĂ©gration des infrastructures actuelles en sciences de la croĂ»te terrestre afin de ne former qu’une seule infrastructure pour que les spĂ©cialistes des sciences de la Terre des quatre coins de l’Europe puissent combiner, modĂ©liser et interprĂ©ter des ensembles de donnĂ©es multidisciplinaires moyennant diverses Ă©chelles de temps et de longueur. Un des principaux objectifs consiste plus particuliĂšrement Ă  intĂ©grer les infrastructures de recherche existantes se rapportant aux domaines de la sismologie, de la gĂ©odĂ©sie, de la gĂ©ophysique, de la gĂ©ologie, de la physique des roches et de la volcanologie Ă  l’échelle paneuropĂ©enne. La valeur ajoutĂ©e de cette intĂ©gration n’est pas visible au moyen des analyses individuelles des donnĂ©es Ă©manant de chaque infrastructure de recherche. Elle doit plutĂŽt ĂȘtre considĂ©rĂ©e Ă  la lumiĂšre d’une perspective Ă  long terme, lorsque les changements qu’impliquent les rĂ©sultats de recherche scientifique actuels auront Ă©tĂ© entiĂšrement rĂ©alisĂ©s et que les incidences sur la sociĂ©tĂ© seront claires. Le systĂšme EPOS est en train d’amorcer sa phase de mise en oeuvre. Cette phase succĂšde Ă  la phase prĂ©paratoire de quatre ans pendant laquelle 18 pays membres de l’Europe ont soumis plus de 250 infrastructures de recherche en vue de l’édification de cette vision paneuropĂ©enne. L’Arctique couvre une grande partie de la plaque europĂ©enne et par consĂ©quent, il joue un rĂŽle important dans les travaux de recherche portant sur la croĂ»te terrestre en Europe. Cependant, le milieu de travail de l’Arctique n’est pas sans dĂ©fis. PremiĂšrement, la majoritĂ© de la limite de la plaque europĂ©enne se trouvant dans l’Arctique est situĂ©e au large, ce qui signifie que des rĂ©seaux marins doivent ĂȘtre amĂ©nagĂ©s pour permettre l’observation de la croĂ»te terrestre. DeuxiĂšmement, de la glace recouvre l’ocĂ©an Arctique, lĂ  oĂč la limite de la plaque europĂ©enne traverse la dorsale de Gakkel, ce qui signifie qu’il faut recourir Ă  des technologies innovatrices pour surveiller la dĂ©formation de la croĂ»te terrestre. C’est pourquoi les travaux de recherche doivent nĂ©cessairement se faire en collaboration avec d’autres disciplines comme l’ocĂ©anographie physique, l’acoustique marine et la gĂ©obiologie. L’établissement d’infrastructures de recherche efficaces capables de faire face Ă  ces conditions rigoureuses s’avĂšre essentiel, tant pour rĂ©duire les coĂ»ts que pour stimuler la recherche multidisciplinaire

    Ambient noise levels and detection threshold in Norway

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    Ambient seismic noise is caused by a number of sources in specific frequency bands. The quantification of ambient noise makes it possible to evaluate station and network performance. We evaluate noise levels in Norway from the 2013 data set of the Norwegian National Seismic Network as well as two temporary deployments. Apart from the station performance, we studied the geographical and temporal variations, and developed a local noise model for Norway. The microseism peaks related to the ocean are significant in Norway. We, therefore, investigated the relationship between oceanic weather conditions and noise levels. We find a correlation of low-frequency noise (0.125–0.25 Hz) with wave heights up to 900 km offshore. High (2–10 Hz) and intermediate (0.5–5 Hz) frequency noise correlates only up to 450 km offshore with wave heights. From a geographic perspective, stations in southern Norway show lower noise levels for low frequencies due to a larger distance to the dominant noise sources in the North Atlantic. Finally, we studied the influence of high-frequency noise levels on earthquake detectability and found that a noise level increase of 10 dB decreases the detectability by 0.5 magnitude units. This method provides a practical way to consider noise variations in detection maps

    An integrated geophysical study of Vestbakken Volcanic Province, western Barents Sea continental margin, and adjacent oceanic crust

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    This paper describes results from a geophysical study in the Vestbakken Volcanic Province, located on the central parts of the western Barents Sea continental margin, and adjacent oceanic crust in the Norwegian-Greenland Sea. The results are derived mainly from interpretation and modeling of multichannel seismic, ocean bottom seismometer and land station data along a regional seismic profile. The resulting model shows oceanic crust in the western parts of the profile. This crust is buried by a thick Cenozoic sedimentary package. Low velocities in the bottom of this package indicate overpressure. The igneous oceanic crust shows an average thickness of 7.2 km with the thinnest crust (5-6 km) in the southwest and the thickest crust (8-9 km) close to the continent-ocean boundary (COB). The thick oceanic crust is probably related to high mantle temperatures formed by brittle weakening and shear heating prior to continental breakup. The COB is interpreted in the central parts of the profile where the velocity structure and Bouguer anomalies change significantly. East of the COB Moho depths increase while the vertical velocity gradient decreases. Below the assumed center for Early Eocene volcanic activity the model shows increased velocities in the crust. These increased crustal velocities are interpreted to represent Early Eocene mafic feeder dykes. East of the zone of volcanoes velocities in the crust decrease and sedimentary velocities are observed at depths of more than 10 km. The amount of crustal intrusions is much lower in this area than farther west. East of the KnĂžlegga Fault crystalline basement velocities are brought close to the seabed. This fault marks the eastern limit of thick Cenozoic and Mesozoic packages on central parts of the western Barents Sea continental margin

    Acoustic waveform inversion for ocean turbulence

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    The seismic oceanography method is based on extracting and stacking the low-frequency acoustic energy scattered by the ocean heterogeneity. However, a good understanding on how this acoustic wavefield is affected by physical processes in the ocean is still lacking. In this work an acoustic waveform modeling and inversion method is developed and applied to both synthetic and real data. In the synthetic example, the temperature field is simulated as a homogeneous Gaussian isotropic random field with the Kolmogorov–Obukhov spectrum superimposed on a background stratified ocean structure. The presented full waveform inversion method is based on the ray-Born approximation. The synthetic seismograms computed using the ray-Born scattering method closely match the seismograms produced with a more computationally expensive finite-difference method. The efficient solution to the inverse problem is provided by the multiscale nonlinear inversion approach that is specifically stable with respect to noise. Full waveform inversion tests are performed using both the stationary and time-dependent sound speed models. These tests show that the method provides a reliable reconstruction of both the spatial sound speed variation and the theoretical spectrum due to fully developed turbulence. Finally, the inversion approach is applied to real seismic reflection data to determine the heterogeneous sound speed structure at the west Barents Sea continental margin in the northeast Atlantic. The obtained model illustrates in more detail the processes of diapycnal mixing near the continental slope. This research was originally published in the Journal of Oceanography. © 2017 American Meteorological Societ
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