A5006615158- Seismic Waves and Analysis
- High-pressure geophysics and materials
- earthquake and tectonic studies
- Seismic Imaging and Inversion Techniques
- Geological and Geochemical Analysis
- Seismology and Earthquake Studies
- Geophysics and Sensor Technology
- Earthquake Detection and Analysis
- Geological and Geophysical Studies
- Cryospheric studies and observations
- Methane Hydrates and Related Phenomena
- Geophysical Methods and Applications
- Landslides and related hazards
- Geophysics and Gravity Measurements
- Planetary Science and Exploration
- Winter Sports Injuries and Performance
- Microwave Imaging and Scattering Analysis
- Geological and Geophysical Studies Worldwide
- Geological Formations and Processes Exploration
- Geochemistry and Geologic Mapping
- Astro and Planetary Science
- Hydrocarbon exploration and reservoir analysis
- Geological Studies and Exploration
- Climate change and permafrost
- Marine and environmental studies
Institut de physique du globe de Paris
2015-2024
Université Paris Cité
2015-2024
University of California, San Diego
2024
Ludwig-Maximilians-Universität München
2024
Centre National de la Recherche Scientifique
2012-2023
Institut Universitaire de France
1998-2023
Sorbonne Paris Cité
2016-2019
Délégation Paris 7
2018
Sorbonne Université
1981-2018
Université Européenne de Bretagne
2010
A data set of 2600 paths for Rayleigh waves and 2170 Love enabled us to retrieve three‐dimensional distributions different seismic parameters. Shallow layer corrections have been carefully performed on phase velocity before regionalization inversion at depth. The parameters include the five a radially anisotropic medium eight azimuthal as defined by Montagner Nataf. It is found that lateral heterogeneities velocities anisotropies in upper mantle are dominated down 250–30 km plate tectonics...
Reference earth models can be retrieved from either body waves or normal-mode eigenperiods. However, there is a large discrepancy between different reference models, which arises partly the type of data set used in their construction and differences parametrization. derived body-wave observations do not give access to density, attenuation factor radial anisotropy. Conversely, normal modes cannot provide correct locations for depth seismic discontinuities, nor associated velocity jump....
We investigate the problem of retrieving anisotropy as a function depth in mantle, from observed azimuthal variations Love and Rayleigh wave velocities. Following approach Smith Dahlen, this dependence is expressed terms Fourier series azimuth θ. For most general case (provided it small enough), some simple linear combinations elastic tensor coefficients are shown to describe total effect (both polarization anisotropy) on propagation surface Waves. that do not depend related transversely...
Understanding the geotectonic evolution of southeastern Tibetan plateau requires knowledge about structure lithosphere. Using data from 77 broadband stations in SW China, we invert Rayleigh wave phase velocity dispersion curves ambient noise interferometry ( T = 10–40 s) and teleseismic surface waves 20–150 for 3‐D heterogeneity azimuthal anisotropy lithosphere to ∼150 km depth. Our array tomography reveals (1) deep crustal zones anomalously low shear speed (2) substantial variations with...
A data set of 2600 paths for Rayleigh waves and 2170 Love was selected in order to resolve azimuthal anisotropy surface the period range 70–250 s. The epicenters were chosen so that provide uniform spatial coverage Earth. synthetic seismogram is computed each path compared observed infer phase velocity along path. To process such a large set, new tomographic technique designed. good correlation found with tectonics whole at shorter periods waves. directions maximum velocities are also well...
We present an azimuthally anisotropic 3-D shear-wave speed model of the Australian upper mantle obtained from dispersion fundamental and higher modes Rayleigh waves. compare two tomographic techniques to map path-average earth models into a for heterogeneity azimuthal anisotropy. Method I uses rectangular surface cell parametrization depth basis functions that represent independently constrained estimates radial structure. It performs iterative inversion with norm damping gradient...
The increasing power of computers and numerical methods (like spectral element methods) allows continuously improving modelization the propagation seismic waves in heterogeneous media development new applications particular time reversal three‐dimensional Earth. concept time‐reversal (hereafter referred to as TR) was previously successfully applied for acoustic many fields like medical imaging, underwater acoustics non destructive testing. We present here first application at global scale TR...
Long-period surface waves from oceanic or atmospheric disturbances can be used for seismic mapping of the upper mantle.
According to different types of observations, the nature lithosphere-asthenosphere boundary (LAB) is controversial. Using a massive data set surface wave dispersions in broad period range (15–300 s), we have developed three-dimensional upper mantle tomographic model (first-order perturbation theory) at global scale. This used derive maps LAB from resolved elastic parameters. The key effects shallow layers and anisotropy are taken into account inversion process. We investigate distribution...
Abstract We present a high‐resolution 3‐D lithospheric model of the Indian plate region down to 300 km depth, obtained by inverting new massive database surface wave observations, using classical tomographic methods. Data are collected from more than 550 seismic broadband stations spanning subcontinent and surrounding regions. The Rayleigh dispersion measurements along ~14,000 paths made in broad frequency range (16–250 s). Our regionalized (group phase) data inverted at depth two steps:...
Abstract Global seismographic networks (GSNs) emerged during the late nineteenth and early twentieth centuries, facilitated by seminal international developments in theory, technology, instrumentation, data exchange. The mid‐ to late‐twentieth century saw creation of World‐Wide Standardized Seismographic Network (1961) International Deployment Accelerometers (1976), which advanced global geographic coverage as seismometer bandwidth increased greatly allowing for recording Earth's principal...
Whether the two large low-shear velocity provinces (LLSVPs) at base of Earth's mantle are wide compact structures extending thousands kilometers upward or bundles distinct plumes is subject debate. Full waveform shear wave tomography deep beneath Indian Ocean highlights presence several separate broad low-velocity conduits anchored core-mantle boundary in eastern part African LLSVP, most clearly La Réunion and Comores hot spots. The plumbing system these spots may also include alternating...
A global‐scale analysis of travel times the mantle Pds phases (converted from P to S discontinuity at a depth d beneath receiver) is presented. Most data are related ′410′ s and ′660′ , recorded by broadband stations Geoscope, Incorporated Research Institutions for Seismology (IRIS) other networks. In order provide good coverage, published measurements 37 complemented our 45 stations. Lateral resolution many higher than that SS its precursors, previously used similar purposes, but we have...
'Vectorial tomography' which enables lateral heterogeneities and anisotropy to be retrieved simultaneously is applied a dataset of dispersion velocities Rayleigh Love waves in the Indian Ocean. Crustal corrections are take account variations shallow parameters. It shown that explained by fewer parameters when azimuthal introduced than only velocity considered. Through hypothesis orthotropy (existence local symmetry axis), we display three-dimensional models S-wave characterized its amplitude...
The understanding of mantle convection is one the most puzzling problems modern geophysics. Among different approaches used by geophysicists to investigate convection, seismic tomography only able visualize, at same time, temperature, petrological anomalies, and flow directions from velocity anisotropy heterogeneities. In order enable a comparison with other geophysical observables, tomographic models are expanded into spherical harmonics. Most agree that down 300–400 km, deep structure...
We present a new method for wave propagation in global earth models based upon the coupling between spectral element and modal solution method. The Earth is decomposed into two parts, an outer shell with 3-D lateral heterogeneities inner sphere only spherically symmetric heterogeneities. Depending on problem, heterogeneous can be mapped as whole mantle or restricted to upper crust. In shell, sought terms of method, which stem from high order variational formulation space second-order...
Seismological studies indicate that the inner core of Earth is anisotropic for compressional waves ( P waves), and has low shear wave S wave) velocity, high seismic attenuation. Using an effective medium theory composite materials, we show presence a volume fraction 3 to 10% liquid in form oblate spheroidal inclusions aligned equatorial plane between iron crystals sufficient explain aforementioned phenomena. Variation -wave velocity polar axis more sensitive addition than waves. The could...
Abstract Seismic investigations are mainly limited by seismic noise. Two microbarometers have been installed in the vault of two different GEOSCOPE stations, one at SSB and other TAM. All vertical components most horizontal show a significant correlation with pressure. In order to correct signals from atmospheric pressure noise, transfer function between data is inverted. Results that, after correction, noise levels reached on similar display below low-noise model as defined Peterson (1993)....
The spectral element method, which provides an accurate solution of the elastodynamic problem in heterogeneous media, is implemented a code, called RegSEM, to compute seismic wave propagation at regional scale. By scale we here mean distances ranging from about 1 km (local scale) 90° (continental scale). advantage RegSEM resides its ability accurately take into account 3-D discontinuities such as sediment-rock interface and Moho. For this purpose, one version code handles local unstructured...
Transient gravity changes are expected to occur at all distances during an earthquake rupture, even before the arrival of seismic waves. Here we report on search such a prompt signal in data recorded by superconducting gravimeter and broadband seismometers 2011 Mw 9.0 Tohoku-Oki earthquake. During exceeding background noise is observed with statistical significance higher than 99% amplitude fraction μGal, consistent sign order magnitude theoretical predictions from first-order model. While...
Gravity gets into the earthquake game Earthquakes generate large movements of mass, which slightly change gravitational field. Unlike elastic waves that propagate from earthquake, gravity perturbations travel at speed light. Vallée et al. have finally observed these in seismometer records great Tohoku Japan 2011. The signal would allowed an accurate magnitude estimation minutes, rather than hours, for this catastrophic earthquake. Science , issue p. 1164