- France
Jean-Paul Montagner
Institut de Physique du Globe de Paris, Seismology, Faculty Member
- Geophysicist, professor at IPG-Paris and University Paris-Diderotedit
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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... 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.
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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... 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.
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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... 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.
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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... 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 ...
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Research Interests: Anisotropy and Isotropy
Global tomographic models have been improved over years not only by an increase in the number of data but more importantly by using more general parameterizations, now including anisotropy (radial anisotropy and then general slight... more
Global tomographic models have been improved over years not only by an increase in the number of data but more importantly by using more general parameterizations, now including anisotropy (radial anisotropy and then general slight anisotropy) and anelasticity. The imaging of seismic anisotropy renews our vision of upper mantle dynamics because different physical processes (cracks or fluid inclusions, lattice preferred orientation of crystals, fine layering) give rise to observable seismic anisotropy (S-wave splitting, surface wave radial and azimuthal anisotropy). Surface waves provide an almost uniform lateral and azimuthal coverages, particularly below oceanic areas and are used to image large scale (>1000km) lateral heterogeneities of velocity and anisotropy in the upper mantle (0-660km depth). The interpretation of anisotropy makes it possible to relate surface geology and plate tectonics to underlying mantle convection processes, and to map at depth the origin of geological objects such as continents, mountain ranges, slabs, ridges and plumes. Usually, several different processes create a complex stratification of anisotropy which can be unraveled by simultaneously taking account of effects of anisotropy on body waves and surface waves. The example of stratification of anisotropy beneath the Horn of Africa will be presented.
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Differentes methodes d'inversion de la vitesse de ces ondes sont appliquees a plusieurs regions du globe: ocean pacifique, afrique, ocean indien. La regionalisation suivant l'age du fond oceanique montre que des heterogeneites... more
Differentes methodes d'inversion de la vitesse de ces ondes sont appliquees a plusieurs regions du globe: ocean pacifique, afrique, ocean indien. La regionalisation suivant l'age du fond oceanique montre que des heterogeneites laterales de vitesse existent jusqu'a au moins 400 km de profondeur et que la correlation entre la tectonique de surface et la structure profonde est meilleure sous l'ocean pacifique que sous l'ocean indien
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This report comprises a presentation of scientific data on subduction earthquakes, on tsunamis and on the Tohoku earthquake. It proposes a detailed description of the French situation (in the West Indies, in metropolitan France, and in... more
This report comprises a presentation of scientific data on subduction earthquakes, on tsunamis and on the Tohoku earthquake. It proposes a detailed description of the French situation (in the West Indies, in metropolitan France, and in terms of soil response), and a discussion of social and economic issues (governance, seismic regulation and nuclear safety, para-seismic protection of constructions). The report is completed by other large documents: presentation of data on the Japanese earthquake, discussion on prediction and governance errors in the management of earthquake mitigation in Japan, discussions on tsunami prevention, on needs of research on accelerometers, and on the seismic risk in France
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Research Interests: Physics and Anisotropy
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The ocean covers two-thirds of the Earth's surface, making it difficult to study the structure of the Earth in these areas. The ocean, however, provides a pressure signal that can be used to study the oceanic crust, by measuring the... more
The ocean covers two-thirds of the Earth's surface, making it difficult to study the structure of the Earth in these areas. The ocean, however, provides a pressure signal that can be used to study the oceanic crust, by measuring the seafloor deformation under this pressure signal. We use continuous signals of seismic ground velocity combined with differential pressure at the sea floor recorded by ocean bottom stations (OBS). By combining pressure and displacement data of the OBS, we can calculate the compliance function from the pressure signal of infra-gravity waves in the frequency band (0.003-0.03 Hz) . The displacement depends on the seismic properties of the earth's crustal layers, primarily its shear modulus.The compliance function is very sensitive to the regions with a low shear velocity which makes it an excellent tool for investigating the earth crust for these regions.To calculate the compliance function, the data must be preprocessed in several steps including glitch and earthquake removal, tilt correction, etc.To remove earthquakes we used earthquake catalogs for large events and a recursive STA/LTA algorithm for local events. We use a combfilter to remove hourly glitches produced by the internal OBS system . Tilt noise is caused by deep ocean currents, we minimize it on the vertical record by rotating the 3-component seismic data to an angle that minimize the variance of the vertical record, then by removing noise coherent with the horizontal components.In this study, we used the French OBS of the Rhum-Rum experiment (Barruol and Sigloch, EOS, 2013) near La Reunion Island for 13 months in 2012, then calculated the compliance function. The crustal shear velocity structure below each station is then recovered by depth inversion of compliance.
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<p>We reconstruct the body and surface waves from the seismic ambient wave field, recorded by a dense seismic array deployment in the Paris Basin, France, with a final objective of performing a 3D seismic tomography by... more
<p>We reconstruct the body and surface waves from the seismic ambient wave field, recorded by a dense seismic array deployment in the Paris Basin, France, with a final objective of performing a 3D seismic tomography by inversion of the retrieved P-phase arrivals. The array was installed in November 2010 and consists of around 100 stations. The stations were shifted to different locations every day, yielding around 580 recording locations with an interstation distance of about 400 m. Each station has continuously recorded around 3-4 days of the seismic ambient wavefield. We calculate the cross-coherency between each station couple in the frequency band of 1.0-4.5 Hz and estimate the empirical Green’s functions. We use the polarization properties of the cross-correlation tensors to separate the P- and Rayleigh wavefields. The results show the reconstruction of the fundamental and higher modes of Rayleigh and Love waves, as well as of diving P- waves. We observe the apparent group velocity of the fundamental and first higher mode of the Rayleigh wave around 0.5 and 1.5 km/s, respectively, and the apparent group velocity of around 0.8 km/s for the fundamental mode of the Love wave. The extraction of the P waves is challenging because of a high amplitude coherent artefact that can cause misinterpretation of the P- wave moveout. We propose a new approach to filter out the extracted P- wave in presence of this artifact and reconstruct the P-wave with a correct apparent velocity of around 2-3 km/s, validated against available active seismic data. This approach is based on template-matching and can be regarded as the most crucial step in P-wave retrieval from our dataset. Future steps will consist of using the extracted P-wave arrival time for a 3D tomography of the anticline structure located beneath the array.</p>
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Knowledge of Martian crust and uppermost mantle aid us studying the planet's evolution. NASA's InSight mission provides seismic data being used to reveal the interior structure. Most studies have focused on the crustal structure... more
Knowledge of Martian crust and uppermost mantle aid us studying the planet's evolution. NASA's InSight mission provides seismic data being used to reveal the interior structure. Most studies have focused on the crustal structure beneath InSight lander, but the seismic structure of other regions has remained poorly known. We use surface‐wave data to investigate the crustal structure of a large region along the Medusa Fossae Formation and the dichotomy. We adopt the largest‐magnitude marsquake (S1222a) that has been recorded, which provides both Rayleigh‐ and Love‐wave signals. We measure and jointly invert these surface‐wave fundamental‐mode group velocities from ∼15 to 40 s to estimate the average 1D isotropic velocity models. These models includes a high‐velocity layer at ∼7‐km depth, which could be due to a regional basaltic activity or regional stress. Our models also indicate that a common intra‐crustal structure (∼12–40 km depth) may exist in this region along the dichotomy.
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<p>One current concern in climate science is the estimations of the amount of ice loss by glaciers each year and the corresponding rate of sea level rise. Greenland ice sheet contribution is significant with about 30% to the global... more
<p>One current concern in climate science is the estimations of the amount of ice loss by glaciers each year and the corresponding rate of sea level rise. Greenland ice sheet contribution is significant with about 30% to the global ice mass losses. Ice loss in Greenland is distributed approximately equally between loss in land by surface melting and loss at the front of marine-terminating glaciers that is modulated by dynamic processes. Dynamic mass loss includes both submarine melting and iceberg calving. The processes that control ablation at tidewater glacier termini, glacier retreat and calving are complex, setting the limits to the estimation of dynamic mass loss and the relation to glacier dynamics. It involves interactions between bedrock &#8211; glaciers &#8211; icebergs &#8211; ice-m&#233;lange &#8211; water &#8211; atmosphere. Moreover, the capsize of cubic kilometer scale icebergs close to a glacier front can destabilize the glacier, generate tsunami waves, and induce mixing of the water column which can impact both the local fauna and flora.</p><p>We aim to improve the understanding of iceberg capsize using a mechanical modeling of iceberg rotation against the glacier terminus, constrained by the generated seismic waves that are recorded at teleseismic distances. To achieve this objective, we develop a fluid-structure interaction model for the capsizing iceberg. Full scale fluid-structure interaction models enable accurate simulation of complex fluid flows in presence of rigid or deformable solids and in presence of free surfaces. However, such models are computationally very expensive. Therefore, our strategy is to construct a simple solid dynamics model involving contact and friction, whose simplified interaction with water is governed by parametrized forces and moments. We fine tune these parametrized effects on an iceberg capsizing in contact with a glacier with the help of reference direct numerical simulations of fluid-structure interactions involving full resolution of Navier-Stokes equations. We assess the sensitivity of the glacier dynamics to the glacier-bedrock friction law and the conditions for triggering a stick-slip motion of the glacier due to iceberg capsize. The seismogenic sources of the capsizing iceberg in contact with a glacier simulated with our model are then compared to the recorded seismic signals for well documented events.</p>
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&lt;p&gt;The interpretation of earthquakes produced by very large glaciers in Greenland and Antarctica (so-called icequakes) due to iceberg calving at the glacier terminus, crevasse opening, and/or sliding of the glacier over the... more
&lt;p&gt;The interpretation of earthquakes produced by very large glaciers in Greenland and Antarctica (so-called icequakes) due to iceberg calving at the glacier terminus, crevasse opening, and/or sliding of the glacier over the bedrock, requires an accurate knowledge of the seismic response of polar ices. On the other hand, the polar ice microstructure plays an important role in glacier dynamics and may be recovered from seismic investigation. Quantification of the effective elastic properties of polycrystalline ice and associated seismic response, possibly anisotropic, and of their strong dependency on the ice microstructure is therefore a key issue. For polar ices, important microstructural features include (i) the strongly pronounced crystallographic texture (LPO) with grains &lt;em&gt;c&lt;/em&gt;-axes typically oriented towards the in-situ vertical direction or aligned with the vertical plane, (ii) the open porosity in the firn (down to ~100m depth), (iii) the air bubble (closed porosity) down to ~1000m depth, (iv) melt pockets in temperate ices, and (v) the inclusion of sand/rocks coming from the bedrock erosion in the ~100m bottom layer. All these microstructures are associated with a large mechanical contrast in the material. To estimate the seismic response of such ices, we make use of a mean-field homogenization model (elastic self-consistent model) that allows estimating the effective elastic properties of polar ices with respect to the microstructural parameters, and the interplay between these parameters. Associated anisotropic seismic response will be discussed and compared with observations. We then propose a reduced-order modeling of the seismic response based on a sparse Proper Generalized Decomposition.&lt;/p&gt;
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Global seismographic networks (GSNs) emerged during the late nineteenth and early twentieth centuries, facilitated by seminal international developments in theory, technology, instrumentation, and data exchange. The mid‐ to late‐twentieth... more
Global seismographic networks (GSNs) emerged during the late nineteenth and early twentieth centuries, facilitated by seminal international developments in theory, technology, instrumentation, and data exchange. The mid‐ to late‐twentieth century saw the creation of the World‐Wide Standardized Seismographic Network (1961) and International Deployment of Accelerometers (1976), which advanced global geographic coverage as seismometer bandwidth increased greatly allowing for the recording of the Earth's principal seismic spectrum. The modern era of global observations and rapid data access began during the 1980s, and notably included the inception of the GEOSCOPE initiative (1982) and GSN (1988). Through continual improvements, GEOSCOPE and the GSN have realized near‐real time recording of ground motion with state‐of‐art data quality, dynamic range, and timing precision to encompass 180 seismic stations, many in very remote locations. Data from GSNs are increasingly integrated with...
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he purpose of the GEOSCOPE Program was the installation of 25 stations in the standard configuration defined by the FDSN (VBB 24 bit, continuous recording at 20 samples/s). The installation is almost complete. The effort this year... more
he purpose of the GEOSCOPE Program was the installation of 25 stations in the standard configuration defined by the FDSN (VBB 24 bit, continuous recording at 20 samples/s). The installation is almost complete. The effort this year focussed on the accessibility of data, either through the IRIS/GOPHER system for large earthquakes, through CD-ROM production, and on line using the Juke-box JUMBO in the GEOSCOPE Data Center (Paris). This aspect will be stressed as the cooperation between IRIS and GEOSCOPE intensifies.
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Recent studies reported the observation of prompt elastogravity signals during the 2011 M9.1 Tohoku earthquake, recorded with broadband seismometers and gravimeter between the rupture onset and the arrival of the seismic waves. Here we... more
Recent studies reported the observation of prompt elastogravity signals during the 2011 M9.1 Tohoku earthquake, recorded with broadband seismometers and gravimeter between the rupture onset and the arrival of the seismic waves. Here we show that to extend the range of magnitudes over which the gravity perturbations can be observed and reduce the time needed for their detection, high‐precision gravity strainmeters under development could be used, such as torsion bars, superconducting gradiometers, or strainmeters based on atom interferometers. These instruments measure the differential gravitational acceleration between two seismically isolated test masses and are initially designed to observe gravitational waves around 0.1 Hz. Our analysis involves simulations of the expected gravity strain signals generated by fault rupture, based on an analytical model of gravity perturbations in a homogeneous half‐space. We show that future gravity strainmeters should be able to detect prompt gra...
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The capsizing of icebergs calved from marine‐terminating glaciers generate horizontal forces on the glacier front, producing long‐period seismic signals referred to as glacial earthquakes. These forces can be estimated by broadband... more
The capsizing of icebergs calved from marine‐terminating glaciers generate horizontal forces on the glacier front, producing long‐period seismic signals referred to as glacial earthquakes. These forces can be estimated by broadband seismic inversion, but their interpretation in terms of magnitude and waveform variability is not straightforward. We present a numerical model for fluid drag that can be used to study buoyancy‐driven iceberg capsize dynamics and the generated contact forces on a calving face using the finite‐element approach. We investigate the sensitivity of the force to drag effects, iceberg geometry, calving style, and initial buoyancy. We show that there is no simple relationship between force amplitude and iceberg volume, and similar force magnitudes can be reached for different iceberg sizes. The force history and spectral content varies with the iceberg attributes. The iceberg aspect ratio primarily controls the capsize dynamics, the force shape, and force frequen...
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... Author Contact Information , E-mail The Corresponding Author , a , b , D. Giardini c , B. Banerdt d , J. Gagnepain-Beyneix a , b , A. Mocquet e , T. Spohn f , JF Karczewski b , g , P. Schibler a , S. Cacho a , WT Pike d , C. Cavoit h... more
... Author Contact Information , E-mail The Corresponding Author , a , b , D. Giardini c , B. Banerdt d , J. Gagnepain-Beyneix a , b , A. Mocquet e , T. Spohn f , JF Karczewski b , g , P. Schibler a , S. Cacho a , WT Pike d , C. Cavoit h , A. Desautez a , M. Favède a , T. Gabsi a , L ...
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Research Interests: Geology and Seismology
Measuring significant and systematic temporal variations of physical parameters is a major goal of seismologists for monitoring seismogenic zones, and eventually forecasting earthquakes. Seismic anisotropy, induced by the crack... more
Measuring significant and systematic temporal variations of physical parameters is a major goal of seismologists for monitoring seismogenic zones, and eventually forecasting earthquakes. Seismic anisotropy, induced by the crack distribution within the continental crust, is very sensitive to stress field changes. So far, anisotropy has been investigated through shear-wave splitting measurements of local earthquakes. In order to get rid of
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1 In his pioneering paper on seismic anisotropy in a layered earth, Anderson (1961) introduced a 2 parameter often referred in global seismology as η without providing any reasoning. This note 3 hopes to clarify the significance of η in... more
1 In his pioneering paper on seismic anisotropy in a layered earth, Anderson (1961) introduced a 2 parameter often referred in global seismology as η without providing any reasoning. This note 3 hopes to clarify the significance of η in the context of the dependence of bodywave velocities in 4 a transversely isotropic system on the angle of incidence, and also its relation with the other 5 well-known anisotropic parameters introduced by Thomsen (1986). 6
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Seismic anisotropy is an effi cient way to investigate the deformation fi eld within the upper mantle. In the framework of rigid tectonic plates, we make use of recent tomographic models of azimuthal anisotropy to derive the best rotation... more
Seismic anisotropy is an effi cient way to investigate the deformation fi eld within the upper mantle. In the framework of rigid tectonic plates, we make use of recent tomographic models of azimuthal anisotropy to derive the best rotation pole of the Pacifi c plate in the uppermost 200 km of the mantle. It is found to be in good agreement with current plate motion (NUVEL1, HS3, and NNR). However, when dividing the Pacifi c plate into two subplates separated by what we refer to as the megagash, an east-west low-velocity and low-anisotropy band extending across the Pacifi c plate from Samoa-Tonga to the Easter-Juan Fernández Islands, the rotation pole of northern Pacifi c is still in agreement with current plate motion but not the rotation pole of the southern part of the Pacifi c, far away from the "classical" rotation pole of the Pacifi c plate. This result suggests a differential motion between the North and South Pacifi c and an ongoing reorganization of plates in the Pacifi c Ocean. The megagash might be a future plate boundary between the North and South Pacifi c plates, associated with the intense volcanism along this band. *jpm@ipgp.fr † Deceased Montagner, J.-P.