Papers by Jean-Paul Montagner
Encyclopedia of earth sciences, 2020
Seismology is usually devoted to the investigation of tectonic earthquakes and imaging of the sol... more Seismology is usually devoted to the investigation of tectonic earthquakes and imaging of the solid structure of the Earth. But with the improvement of seismometers and the explosion of the continuous recording of the ground motion by broadband seismic networks, other phenomena can be investigated. Since seismometers are sensitive to any kind of ground displacement, small events hidden in the noise can be detected. A large part of these small events is related to the interaction or the coupling of the surface of the solid Earth with its surficial unconsolidated solids, fluid/gas enveloppes (ocean and atmosphere). Iceberg calving, glacier dynamics, landslides, snow avalanches, hurricanes, ocean waves belong to this kind of environmental events, able to generate observable seismic signals. Microseisms permanently excited by the interaction of gravity waves and swells in oceans, fluvial seismic signals make it necessary to use statistical approaches for extracting useful information on the source processes in a broad frequency range. In contrast to microseisms, other events are episodic, deterministic, some of them well located in space and time, can be individually investigated. The study of all these natural phenomena giving rise to observable seismic signals constitute the field of environmental seismology.
Due to the faintness of the associated signals, new methods and techniques have been used. For deterministic events, beamforming methods, time-reversal methods or its less general form, back-projection technique (see Larmat et al., this issue for all references), have been applied to locate them in space and time. Microseisms were investigated since Wiechert (1904) and physical processes to explain them were proposed many decades ago (Longuet-Higgins, 1950, Hasselman, 1963). For a stochastic approach of ambient noise, the cross-correlation methods of signals between two seismic stations are now routinely used and make it possible to retrieve the empirical Green’s function (impulse response of the propagating medium) between these two stations (see Campillo et al., this issue). They are particularly well suited for monitoring physical parameters such as variation in the subsoil temperature, aquifers, climate and global changes.
Environmental seismology can be distinguished from “anthropic seismology”, including the study of seismic signals associated with anthropic activity, such as nuclear, mining explosions, attacks, triggered events, urban seismology (traffic, footquakes …) eventhough similar methods can be used to study them.
Research Square (Research Square), Aug 2, 2023
Seismic anisotropy in the upper mantle reveals geodynamic processes and the tectonic evolution of... more Seismic anisotropy in the upper mantle reveals geodynamic processes and the tectonic evolution of the Earth. The two most powerful methods, surface wave tomography, and shear-wave splitting observations, cannot investigate the deep local anisotropy with good vertical and lateral resolution, resulting in poor constraints on plate deformation processes of the complex plate boundary beneath the Southern California region. Here, we show that the amplitude ratio of translational displacement and rotation makes it possible to retrieve the local anisotropy in the upper mantle. Azimuthal anisotropy in the asthenosphere is well determined and resolved in lateral and vertical directions. The fast axis retrieved from the amplitude observation indicates the local rapid changes in plate deformation and complex pattern of mantle flow, which is compatible with the distributions of horizontal mantle flow illuminated by geodetic measurements, providing new insights on geodynamic processes of the Southern California region.
A new approach is proposed for measuring the local dispersion curves of surface waves in weakly a... more A new approach is proposed for measuring the local dispersion curves of surface waves in weakly anisotropic media using a single, multi-component station, which consists of translation and rotation or strain. We directly extract the local azimuth-dependent phase velocity of the Rayleigh wave from the 6C amplitude ratio using seismic arrays deployed in Southern California. The extracted dispersion curves match well with the theoretical 2φ azimuthal anisotropy term. And the estimated fast wave direction is also consistent well with results calculated from SKS and beamforming methods which demonstrates the feasibility of studying local seismic anisotropy directly from 6C amplitude observations.
Proceedings, Jun 1, 2015
We present here Scholte and Love wave phase velocity tomography at the Valhall Oil Field using am... more We present here Scholte and Love wave phase velocity tomography at the Valhall Oil Field using ambient noise recorded by a network of 3D multi-component ocean bottom cable. We have cross-correlated 6.5 hours of continuous recording of noise between vertical-vertical (ZZ), radial-radial (RR), and transverse-transverse (TT) components. After applying an F-K filter, we were able to extract the first overtone of Scholte waves at Valhall from the RR cross-correlations. We then used the filtered overtone waveforms to measure inter-station frequency-dependent phase time delays and constructed 2D phase-velocity maps with the Eikonal tomography method. Furthermore, we compute average dispersion curves for Scholte and Love waves by combining information from more than 10 millions of individual cross-correlations. We use the Neighbourhood algorithm to invert jointly these dispersion curves and to obtain an average 1D anisotropic model of the Valhall overburden down to depths of ~1 km. We find a significant radial anisotropy at depths below 600 m. This average 1D model is used as a reference model for the 3D inversion.
Science Advances, Jan 27, 2023
Whether the two large low–shear velocity provinces (LLSVPs) at the base of Earth’s mantle are wid... more Whether the two large low–shear velocity provinces (LLSVPs) at the base of Earth’s mantle are wide compact structures extending thousands of kilometers upward or bundles of distinct mantle plumes is the subject of debate. Full waveform shear wave tomography of the deep mantle beneath the Indian Ocean highlights the presence of several separate broad low-velocity conduits anchored at the core-mantle boundary in the eastern part of the African LLSVP, most clearly beneath La Réunion and Comores hot spots. The deep plumbing system beneath these hot spots may also include alternating vertical conduits and horizontal ponding zones, from 1000-km depth to the top of the asthenosphere, reminiscent of dyke and sills in crustal volcanic systems, albeit at a whole-mantle scale.
Many imaging techniques depend on the fact that the waves used for imaging are invariant for time... more Many imaging techniques depend on the fact that the waves used for imaging are invariant for time reversal. The physical reason for this is that in imaging one propagates the recorded waves backward in time to the place and time when the waves interacted with the medium. In this chapter, the invariance for time reversal is shown for Newton's law, Maxwell's equations, the Schrödinger equation and the equations of fluid mechanics. The invariance for time reversal can be used as a diagnostic tool to study the stability of the temporal evolution of systems. This is used to study the relation between classical chaos and wave chaos, which also has implications for quantum chaos. The main conclusion is that in classical chaos perturbations in the system grow exponentially in time [exp (µt)], whereas for the corresponding wave system perturbations grow at a much smaller rate algebraically with time (√ t).
HAL (Le Centre pour la Communication Scientifique Directe), Apr 1, 2012
International audienc
AGU Fall Meeting Abstracts, Dec 1, 2001
EGU General Assembly Conference Abstracts, Apr 1, 2016
Journal Of Geophysical Research: Solid Earth, Aug 1, 2021
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Birkhäuser Basel eBooks, 1998
During the last 30 years, considerable evidence of seismic anisotropy has accumulated demonstrat... more During the last 30 years, considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales, but not in all depth ranges. We detail which conditions are necessary to detect large-scale seismic anisotropy. Firstly, minerals must ...
Special papers, Aug 29, 2015
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Papers by Jean-Paul Montagner
Due to the faintness of the associated signals, new methods and techniques have been used. For deterministic events, beamforming methods, time-reversal methods or its less general form, back-projection technique (see Larmat et al., this issue for all references), have been applied to locate them in space and time. Microseisms were investigated since Wiechert (1904) and physical processes to explain them were proposed many decades ago (Longuet-Higgins, 1950, Hasselman, 1963). For a stochastic approach of ambient noise, the cross-correlation methods of signals between two seismic stations are now routinely used and make it possible to retrieve the empirical Green’s function (impulse response of the propagating medium) between these two stations (see Campillo et al., this issue). They are particularly well suited for monitoring physical parameters such as variation in the subsoil temperature, aquifers, climate and global changes.
Environmental seismology can be distinguished from “anthropic seismology”, including the study of seismic signals associated with anthropic activity, such as nuclear, mining explosions, attacks, triggered events, urban seismology (traffic, footquakes …) eventhough similar methods can be used to study them.
Due to the faintness of the associated signals, new methods and techniques have been used. For deterministic events, beamforming methods, time-reversal methods or its less general form, back-projection technique (see Larmat et al., this issue for all references), have been applied to locate them in space and time. Microseisms were investigated since Wiechert (1904) and physical processes to explain them were proposed many decades ago (Longuet-Higgins, 1950, Hasselman, 1963). For a stochastic approach of ambient noise, the cross-correlation methods of signals between two seismic stations are now routinely used and make it possible to retrieve the empirical Green’s function (impulse response of the propagating medium) between these two stations (see Campillo et al., this issue). They are particularly well suited for monitoring physical parameters such as variation in the subsoil temperature, aquifers, climate and global changes.
Environmental seismology can be distinguished from “anthropic seismology”, including the study of seismic signals associated with anthropic activity, such as nuclear, mining explosions, attacks, triggered events, urban seismology (traffic, footquakes …) eventhough similar methods can be used to study them.