Search

Showing total 6 results
Start Over Topic geophysics
6 results

1. Ambient seismic noise imaging of the lowermost mantle beneath the North Atlantic Ocean

Author

Pierre Boué, Lise Retailleau, Michel Campillo, Lei Li, Observatoire Volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris, Institut des Sciences de la Terre (ISTerre), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Grenoble Alpes (UGA)-Université Gustave Eiffel-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry]), Institut de Physique du Globe de Paris (IPG Paris), Department of Geophysics [Stanford], Stanford EARTH, Stanford University-Stanford University, Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Gustave Eiffel-Université Grenoble Alpes (UGA), and The data set was downloaded and processed using python and the seismological community scientific library obspy (Krischer et al. 2015). The figures were produced using Python and MATLAB and the Python module basemap was used to produce the map. The facilities of IRIS Data ervices, and specifically the IRIS Data Management Center, were used for access to waveforms, related metadata, and/or derived products used in this study. IRIS Data Downloaded from https://academic.oup.com/gji/article-abstract/222/2/1339/5827640 by CNRS user on 23 June 2020Services are funded through the Seismological Facilities for the Advancement of Geoscience (SAGE)Award of theNational Science Foundation under Cooperative Support Agreement EAR-1851048.The computation of the correlation functions presented in this paper was performed performed using the GRICAD infrastructure (https://gricad.univ-grenoble-alpes.f r), which is partly supported by the Equip@Meso project (reference ANR-10-EQPX-29–01) of the programme Investissements d’Avenir supervised by the Agence Nationale pour la Recherche. This work has been supported by a grant from Labex OSUG@2020 (Investissements d’avenir—ANR10 LABX56) and Fondation Simone et Cino Del Duca, Institut de France (Prix scientifique 2013). We acknowledge the support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grantagreement No 742335, F-IMAGE). The research of LR was supported by Pacific Gas and Electric. We thank K. Schaukowitch and the Hume centre for writing and speaking at Stanford for useful comments that helped us to improve the manuscript. We thank the Editor, Michael Ritzwoller, St´ephanie Durand and two anonymousreviewers for their comments and suggestions which helped to improve the quality of this paper

Subjects
Composition and structure of the mantle, Seismic noise, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Frequency band, Body waves, Cosmic microwave background, body waves, 010502 geochemistry & geophysics, 01 natural sciences, Mantle (geology), Physics::Geophysics, Core-Mantle-Boundary, Geochemistry and Petrology, Time-series analysis, Core–mantle boundary, 14. Life underwater, Atlantic Ocean, 0105 earth and related environmental sciences, Ambient noise correlations, Microseism, Reflectivity, Geophysics, 13. Climate action, Seismology, Geology
Abstract

SUMMARY Body waves can be extracted from correlation functions computed from seismic records even at teleseismic distances. Here we use P and PcP waves from the secondary microseism frequency band that are propagating between Europe and the Eastern United States to image the core–mantle boundary (CMB) and D” structure beneath the North Atlantic. This study presents the first 3-D image of the lower mantle obtained from ocean-generated microseism data. Robustness of our results is evaluated by comparing images produced by propagation in both directions. Our observations reveal complex patterns of lateral and vertical variations of P-wave reflectivity with a particularly strong anomaly extending upward in the lower mantle up to 2600 km deep. We compare these results with synthetic data and associate this anomaly to a Vp velocity increase above the CMB. Our image aims at promoting the study of the lower mantle with microseism noise excitations.

Published
2020

2. The Dominant Role of Brewer‐Dobson Circulation on 17 O‐Excess Variations in Snow Pits at Dome A, Antarctica

Author

Hongxi Pang, Peng Zhang, Shuangye Wu, Jean Jouzel, Hans Christian Steen‐Larsen, Ke Liu, Wangbin Zhang, Jinhai Yu, Chunlei An, Deliang Chen, Shugui Hou, Nanjing University (NJU), University of Gothenburg (GU), University of Dayton, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Glaces et Continents, Climats et Isotopes Stables (GLACCIOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), University of Bergen (UiB), Polar Research Institute of China (PRIC), and We thank all of the CHINARE-26 and CHINARE-32 scientists, technicians, and porters for their hard work in the field. We thank Amaelle Landais (LSCE) for the 17O-excess measurements and her constructive comments on this paper. We also thank Tongmei Wang for her advice on calculating the residual circulation. This work was jointly supported by the National Natural Science Foundation of China (41622605, 41830644, 91837102, 42021001), the Chinese Arctic and Antarctic Administration (CXPT2020012), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and the Swedish STINT (CH2019-8377).

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Atmospheric Science, Geophysics, Space and Planetary Science, Earth and Planetary Sciences (miscellaneous), [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment
Abstract

Recent studies have suggested that water isotopologues in snow pits from remote East Antarctica can be influenced by the input of stratospheric water, which has anomalously high 17O-excess values. However, it remains unclear whether the 17O-excess records preserved in snow and ice from this region can be used to reconstruct stratosphere-troposphere exchange (STE). In this study, we present high-resolution 17O-excess records from two snow pits at Dome A, the highest point of the Antarctic ice sheet. The 17O-excess records show a significant positive correlation with the strength of the Brewer-Dobson circulation (BDC), the hemispheric-scale troposphere-stratosphere overturn circulation. Stronger BDC leads to more stratospheric water input over Antarctica and higher 17O-excess, and vice versa. In addition, the 17O-excess records also have a significant positive correlation with the Southern Annular Mode (SAM) index, because SAM modulates Antarctic precipitation, which has a dilution effect on the stratospheric water input. The 17O-excess records do not show significant correlations with local temperature and relative humidity in the moisture source region. These results suggest the dominant effect of BDC on 17O-excess and indicate the potential for using 17O-excess records in ice cores from remote sites in East Antarctica for reconstructing long-term variations of STE, and understanding their mechanisms and climate effects. publishedVersion

Published
2022

3. Seismic Mapping of Subglacial Hydrology Reveals Previously Undetected Pressurization Event

Author

Celeste R. Labedz, Timothy C. Bartholomaus, Jason M. Amundson, Florent Gimbert, Marianne S. Karplus, Victor C. Tsai, Stephen A. Veitch, Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Seismological Laboratory, California Institute of Technology, California Institute of Technology (CALTECH), and This work was made possible in part by hard work in the field by Margot Vore, Daniel Bowden, Galen Kaip, and the students and staff of the 2017 Juneau Icefield Research Program. We especially thank Matt Beedle for provision of the photogrammetrically-produced DEM of Lake Linda, following lake drainage. This work was also aided by the advice of Mike Gurnis and Rob Clayton. We thank Paul Winberry and two anonymous reviewers for their helpful feedback, which improved this paper greatly. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1745301. This work was made possible in part by a University of Idaho seed grant, #FY18-01. DEM provided by the Polar Geospatial Center under NSF-OPP awards 1043681, 1559691, and 1542736.

Subjects
Geophysics, environmental seismology, cryoseismology, [SDU]Sciences of the Universe [physics], [SDE]Environmental Sciences, glaciology, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, seismology, glacier hydrology, Earth-Surface Processes
Abstract

International audience; Understanding the dynamic response of glaciers to climate change is vital for assessing water resources and hazards, and subglacial hydrology is a key player in glacier systems. Traditional observations of subglacial hydrology are spatially and temporally limited, but recent seismic deployments on and around glaciers show the potential for comprehensive observation of glacial hydrologic systems. We present results from a high-density seismic deployment spanning the surface of Lemon Creek Glacier, Alaska. Our study coincided with a marginal lake drainage event, which served as a natural experiment for seismic detection of changes in subglacial hydrology. We observed glaciohydraulic tremor across the surface of the glacier that was generated by the subglacial hydrologic system. During the lake drainage, the relative changes in seismic tremor power and water flux are consistent with pressurization of the subglacial system of only the upper part of the glacier. This event was not accompanied by a significant increase in glacier velocity; either some threshold necessary for rapid basal motion was not attained, or, plausibly, the geometry of Lemon Creek Glacier inhibited speedup. This pressurization event would have likely gone undetected without seismic observations, demonstrating the power of cryoseismology in testing assumptions about and mapping the spatial extent of subglacial pressurization.

Published
2022

4. Ambient noise surface wave tomography to determine the shallow shear velocity structure at Valhall: depth inversion with a Neighbourhood Algorithm

Author

Aurélien Mordret, Satish C. Singh, N. M. Shapiro, Philippe Roux, Matthieu Landès, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Sismologie (IPGP), Institut de Physique du Globe de Paris, Institut des Sciences de la Terre (ISTerre), Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-PRES Université de Grenoble-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), European Grid Infrastructure. For more information, please consult the EGI-InSPIRE paper (http://go.egi.eu/pdnon), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPG Paris), Centre National de la Recherche Scientifique (CNRS)-PRES Université de Grenoble-Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry]), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), and Institut des Sciences de la Terre, Universit´e Joseph Fourier, CNRS UMR 5275, Maison des G´eosciences, 1381 Rue de la Piscine, F-38400 Saint Martin d’H`eres, France

Subjects
Seismic tomography, 010504 meteorology & atmospheric sciences, Ambient noise level, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Inversion (meteorology), 010502 geochemistry & geophysics, Geodesy, 01 natural sciences, Geophysics, [SDU]Sciences of the Universe [physics], Geochemistry and Petrology, Surface wave, Tomography, Shear velocity, Surface waves and free oscillations, Seismology, Geology, 0105 earth and related environmental sciences
Abstract

International audience; S U M M A R Y This study presents a depth inversion of Scholte wave group and phase velocity maps obtained from cross-correlation of 6.5 hr of noise data from the Valhall Life of Field Seismic network. More than 2 600 000 vertical-vertical component cross-correlations are computed from the 2320 available sensors, turning each sensor into a virtual source emitting Scholte waves. We used a traditional straight-ray surface wave tomography to compute the group velocity map. The phase velocity maps have been computed using the Eikonal tomography method. The inversion of these maps in depth are done with the Neighbourhood Algorithm. To reduce the number of free parameters to invert, geological a priori information are used to propose a power-law 1-D velocity profile parametrization extended with a gaussian high-velocity layer where needed. These parametrizations allowed us to create a high-resolution 3-D S-wave model of the first 600 m of the Valhall subsurface and to precise the locations of geological structures at depth. These results would have important implication for shear wave statics and monitoring of seafloor subsidence due to oil extraction. The 3-D model could also be a good candidate for a starting model used in full-waveform inversions.

Published
2014

5. Variability in fluence and spectrum of high-energy photon bursts produced by lightning leaders

Author

Wei Xu, Sebastien Celestin, Victor P. Pasko, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Communications and Space Sciences Laboratory [PennState] (CSSL), Pennsylvania State University (Penn State), Penn State System-Penn State System, and Part of the simulation results presented in this paper has been obtained using the computer cluster at the Centre de Calcul Scientifique en région Centre (CCSC).

Subjects
Physics, [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph], Photon, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Astrophysics::High Energy Astrophysical Phenomena, Gamma ray, Electron, Astrophysics, Photon energy, 01 natural sciences, 7. Clean energy, Fluence, Lightning, Spectral line, Corona (optical phenomenon), Geophysics, 13. Climate action, Space and Planetary Science, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract

International audience; In this paper, we model the production and acceleration of thermal runaway electrons during negative corona flash stages of stepping lightning leaders and the corresponding terrestrial gamma ray flashes (TGFs) or negative cloud-to-ground (−CG) lightning-produced X-ray bursts in a unified fashion. We show how the source photon spectrum and fluence depend on the potential drop formed in the lightning leader tip region during corona flash and how the X-ray burst spectrum progressively converges toward typical TGF spectrum as the potential drop increases. Additionally, we show that the number of streamers produced in a negative corona flash, the source electron energy distribution function, the corresponding number of photons, and the photon energy distribution and transport through the atmosphere up to low-orbit satellite altitudes exhibit a very strong dependence on this potential drop. This leads to a threshold effect causing X-rays produced by leaders with potentials lower than those producing typical TGFs extremely unlikely to be detected by low-orbit satellites. Moreover, from the number of photons in X-ray bursts produced by −CGs estimated from ground observations, we show that the proportionality between the number of thermal runaway electrons and the square of the potential drop in the leader tip region during negative corona flash proposed earlier leads to typical photon fluences on the order of 1 ph/cm2 at an altitude of 500 km and a radial distance of 200 km for intracloud lightning discharges producing 300 MV potential drops, which is consistent with observations of TGF fluences and spectra from satellites.

Published
2015

6. Statistics of whistler mode waves in the outer radiation belt: Cluster STAFF-SA measurements

Author

Michael A. Balikhin, Hugo Breuillard, Didier Mourenas, Oleksiy Agapitov, G. Rolland, Vladimir Krasnoselskikh, Yuri V. Khotyaintsev, Anton Artemyev, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Swedish Institute of Space Physics [Kiruna] (IRF), Centre d'Études de Limeil-Valenton (CEA-DAM), Direction des Applications Militaires (DAM), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Department of Automatic Control and Systems Engineering, University of Sheffield [Sheffield], Centre National d'Études Spatiales [Toulouse] (CNES), for their assistance in evaluating this paper. This work was supported by CNES through the grant 'Modeles d’ondes' and Cluster Co-I DWP.Swedish Research Council, grant 2007-4377, and European Project: 284520,EC:FP7:SPA,FP7-SPACE-2011-1,MAARBLE(2012)

Subjects
Physics, Hiss, 010504 meteorology & atmospheric sciences, Whistler, Wave propagation, 01 natural sciences, Physics::Geophysics, L-shell, symbols.namesake, Geophysics, Amplitude, Earth's magnetic field, Space and Planetary Science, Surface wave, [SDU]Sciences of the Universe [physics], Van Allen radiation belt, 0103 physical sciences, Statistics, Physics::Space Physics, symbols, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract

International audience; [1] ELF/VLF waves play a crucial role in the dynamics of the radiation belts and are partly responsible for the main losses and the acceleration of energetic electrons. Modeling wave-particle interactions requires detailed information of wave amplitudes and wave normal distribution over L-shells and over magnetic latitudes for different geomagnetic activity conditions. We performed a statistical study of ELF/VLF emissions using wave measurements in the whistler frequency range for 10 years (2001–2010) aboard Cluster spacecraft. We utilized data from the STAFF-SA experiment, which spans the frequency range from 8 Hz to 4 kHz. We present distributions of wave magnetic and electric field amplitudes and wave normal directions as functions of magnetic latitude, magnetic local time, L-shell, and geomagnetic activity. We show that wave normals are directed approximately along the background magnetic field (with the mean value of  — the angle between the wave normal and the background magnetic field, about 10 ı –15 ı) in the vicinity of the geomagnetic equator. The distribution changes with magnetic latitude: Plasmaspheric hiss normal angles increase with latitude to quasi-perpendicular direction at 35 ı –40 ı where hiss can be reflected; lower band chorus are observed as two wave populations: One population of wave normals tends toward the resonance cone and at latitudes of around 35 ı –45 ı wave normals become nearly perpendicular to the magnetic field; the other part remains quasi-parallel at latitudes up to 30 ı. The observed angular distribution is significantly different from Gaussian, and the width of the distribution increases with latitude. Due to the rapid increase of  , the wave mode becomes quasi-electrostatic, and the corresponding electric field increases with latitude and has a maximum near 30 ı. The magnetic field amplitude of the chorus in the day sector has a minimum at the magnetic equator but increases rapidly with latitude with a local maximum near 12 ı –15 ı. The wave magnetic field maximum is observed in the night sector at L > 7 during low geomagnetic activity (at L 5 for K p > 3). Our results confirm the strong dependence of wave amplitude on geomagnetic activity found in earlier studies. (2013), Statistics of whistler-mode waves in the outer radiation belt: Cluster STAFF-SA measurements

Published
2013