Papers by Geneviève roult
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1995
On April 5 2007, the largest historical caldera collapse of the summit of the Piton de la Fournaise volcano occurred and continued over 9 days. A 340 m deep collapse of the caldera floor was measured at the end of the collapse episode. The volcano's most voluminous eruption in the last two centur...
International audienc
Leg 179 is a two-part leg composed of testing the hammer drill-in casing system developed at the ... more Leg 179 is a two-part leg composed of testing the hammer drill-in casing system developed at the Ocean Drilling Program (ODP) and drilling a hole for the Ninetyeast Ridge Observatory (NERO) Project. Testing of the hammer drill will determine the viability of the tool, the complete casing system, and the maximum slope that can be spudded by the tool. Fifteen days have been allocated for these tests. The NERO project will enable a major gap in the global coverage of seismic, magnetic, and general geophysical data to be filled. Currently, geophysical observatories are only present on continents and islands, thus data collection is incomplete. Establishing a cased reentry hole will be the first step toward the installation of a Geophysical Ocean Bottom Observatory. This observatory will be part of the future network of seafloor observatories proposed in the International Ocean Network (ION) program. From a scientific point of view, the geophysical applications can be considered at two d...
Variations temporelles de la gravité en relation avec la dynamique interne de la Terre Apport des... more Variations temporelles de la gravité en relation avec la dynamique interne de la Terre Apport des gravimètres supraconducteurs présentée par
Understanding the Dynamics of the February-April 2007 Eruptions of the Piton de la Fournaise and the Related Caldera Collapse from a Single Very Broad-band Seismic Station
The 26th December 2004 Sumatran-Andaman mega-event: observed and synthetic spectra computed from complex sources and various models
ABSTRACT
Seismic Noise Level at Geoscope
Bulletin of the Seismological Society of America
The 26th December 2004 Sumatra-Andaman event: an important step towards a density profile model in a near future?
ABSTRACT
Erratum: The GEOSCOPE Program: Progress and Challenges during the Past 30 Years
International audienc
GEODIS: A Portable Ocean Bottom Very Broadband Seismic Station
The last ten years have seen the simultaneous development of a global seismic network coordinated... more The last ten years have seen the simultaneous development of a global seismic network coordinated through the FDSN (Federation of Digital Seismograph Networks) and of portable broadband seismic arrays. The same approach can be followed for improving our scientific understanding of the Earth processes below oceanic areas. Both components of ocean bottom geophysical networks, will be coordinated by ION (international
The GEOSCOPE program: state of the art in 2005
The GEOSCOPE program was launched in 1982 by the National Institute of Sciences of Universe (INSU... more The GEOSCOPE program was launched in 1982 by the National Institute of Sciences of Universe (INSU), a department of the French National Center of Scientific Research (CNRS), at the instigation of the Institute of Physics of the Earth of Paris (IPGP). The purpose was the installation of about 25 stations well distributed worldwide (in particular in the southern hemisphere), in
Challenges of the GEOSCOPE Observatory
The GEOSCOPE observatory consists of a global seismic network and a data center. The observatory ... more The GEOSCOPE observatory consists of a global seismic network and a data center. The observatory was launched in 1982 by the French National Center of Scientific Research (CNRS/INSU) and progressively 30 stations have been installed across all continents and on islands throughout the oceans. The GEOSCOPE stations are located on 18 countries and equipped with three component very broad-band seismometers (STS1 or STS2) and 24 or 26 bit digitizers, as required by the Federation of Seismic Digital Network (FDSN). In most stations a pressure gauge and a thermometer are also installed. During the last years, 13 stations have been upgraded in order to send data in real or near real time to GEOSCOPE Data Center. In 2008, two new real time stations will be installed in the Indian Ocean: in the South of Madagascar and on Rodrigues island. Four stations in the Carribean region and in South America will also be upgraded to send real time data to GEOSCOPE Data Center and to local tsunami warning...
Robust Computation of Global Surface Wave Phase Velocity Maps from Massive Dataset by the Clash
The detection of seismic wave velocity heterogeneities enables to generate a present-day snapshot... more The detection of seismic wave velocity heterogeneities enables to generate a present-day snapshot of the deep interior of the Earth. One modus operandi to compute a 3D body wave velocity model relies on the surface wave phase velocity measurements. Using a roller-coaster type algorithm, we determine the phase velocities of the fundamental and the first six overtone, integrated over the great circle epicenter-station paths. This new non-linear inverse approach tends to introduce the minimum number of a priori conditions. Every solution is tested and the model which achieves the best misfit function is retained. For each frequency of a given mode-branch, phase velocities are then expressed in terms of global heterogeneity maps. To this end, a new method, which includes azimuthal anisotropy in its comprehensive form, is developed and is reverently baptized the Computation of Large Anisotropic Seismic Heterogeneities (CLASH). The surface of the Earth is regularly discretized by means of...
New observations of Q quality factors of a few gravest normal modes from superconducting gravimeters of the Global Geodynamics Project (GGP)
The high quality of the GGP superconducting gravimeters contributes to the clear observation of s... more The high quality of the GGP superconducting gravimeters contributes to the clear observation of seismic normal modes at frequencies lower than 1mHz and offers a good opportunity for studying the behaviour of these modes. The interest of scientists for the gravest normal modes is due to the fact that these modes do contribute to a better knowledge of the density profile in the Earth, helping to constrain Earth's models. These modes have been clearly identified after some large recent events recorded on superconducting gravimeters. The Peruvian earthquake of June 2001 provided us with individual spectra (in a unique station) with a clear splitting of the fundamental mode 0S2 and identification of each of the five individual singlets, with a resolution never obtained from broad-band seismometers records. The Q quality factors have been determined from the apparent decrease of the amplitude of each singlet with time, according to a well suited technique (Roult and Clevede, 2000). T...
The GEOSCOPE Program : state of the art in 2004
The GEOSCOPE program was launched in 1982 by the National Institute of Sciences of Universe (INSU... more The GEOSCOPE program was launched in 1982 by the National Institute of Sciences of Universe (INSU), a department of the French National Center of Scientific Research (CNRS), at the instigation of the Institute of Physics of the Earth of Paris (IPGP). The purpose of the GEOSCOPE program was the installation of about 25 stations well distributed worldwide (in particular in the southern hemisphere), in the standard configuration defined by the FDSN (very broad-band 24 bit, continuous recording at 20sps). The GEOSCOPE program is operating 28 digital very-broadband stations. Data from large events are teletransmitted for some stations (by phone line or through internet) and made available within one day. A satellite transmission system is now working, in cooperation with the french military agency CEA/DASE, in cooperation with CTBTO (Dzumac in New Caledonia). An agreement between GEOSCOPE and CTBTO allows us to get data continuously and with a low gain. The next CTBTO stations to be inst...
Tectonophysics, 2003
As a contribution to the study of high-latitude seismicity on the Antarctica plate, we have devel... more As a contribution to the study of high-latitude seismicity on the Antarctica plate, we have developed a procedure to identify and locate previously unnoticed earthquakes by using broadband records of 29 stations operating in the Southern Hemisphere. A first approach of the method consists of visually examining continuous records from GEOSCOPE and GSN stations for Rayleigh-waves associated with earthquakes missing in the NEIC monthly catalogue. Two hundred ten earthquakes were identified that had no corresponding locations in the 1999 NEIC catalogue. Among them, 88 events, with magnitude ranging from 3.7 to 5.2, and identified on at least four stations, have been located by using an epicenter location algorithm based on regional Rayleigh-wave propagation models. The precision of the location, depending both on the selected propagation model and the phase picking accuracy, is around 100 km. Most of the reported earthquakes occurred on the plate boundaries, principally along the South-Indian and Pacific ridges. A few epicenters have been located inside the Antarctica plate, far from the plate limits. Among them, only two earthquakes occurring on the continent itself are reported. About half of the events located in our study are reported by the PIDC (Prototype International Data Center). Three earthquakes, with magnitudes ranging from 4.7 to 5.2, reported neither by NEIC nor by PIDC, are sufficiently energetic to be recorded in most broad-band stations operating around the world. Considerations concerning the local crustal structure and the physical processes at the source are involved in interpreting these observations.
Tectonophysics, 2008
The Afar area is one of the biggest continental hotspots active since about 30Ma. It may be the s... more The Afar area is one of the biggest continental hotspots active since about 30Ma. It may be the surface expression of a mantle "plume" related to the African Superswell. Central Africa is also characterized by extensive intraplate volcanism. Around the same time (30Ma), volcanic activity restarted in several regions of the African plate and hotspots such as Darfur, Tibesti, Hoggar and Mount Cameroon, characterized by a significant though modest volcanic production. The interactions of mantle upwelling with asthenosphere, lithosphere and crust remain unclear and seismic anisotropy might help in investigating these complex interactions. We used data from the global seismological permanent FDSN networks (GEOSCOPE, IRIS, MedNet, GEO-FON, etc.), from the temporary PASSCAL experiments in Tanzania and Saudi Arabia and a French deployment of 5 portable broadband stations surrounding the Afar Hotspot. A classical two-step tomographic inversion from surface waves performed in the Horn of Africa with selected Rayleigh wave and Love wave seismograms leads to a 3D-model of both S V velocities and azimuthal anisotropy, as well as radial S H /S V anisotropy, with a lateral resolution of 500km. The region is characterized by low shear-wave velocities beneath the Afar Hotspot, the Red Sea, the Gulf of Aden and East of the Tanzania Craton to 400km depth. High velocities are present in the Eastern Arabia and the Tanzania Craton. The results of this study enable us to rule out a possible feeding of the Central Africa hotspots from the "Afar plume" above 150-200km. The azimuthal anisotropy displays a complex pattern near the Afar Hotspot. Radial anisotropy, although poorly resolved laterally, exhibits S H slower than S V waves down to about 150km depth, and a reverse pattern below. Both azimuthal and radial anisotropies show a stratification of anisotropy at depth, corresponding to different physical processes. These results suggest that the Afar hotspot has a different and deeper origin than the other African hotspots (Darfur, Tibesti, Hoggar). These latter hotspots can be traced down to 200km from S-wave velocity but have no visible effect on radial and azimuthal anisotropy.
Physics of the Earth and Planetary Interiors, 1994
To improve the lateral resolution of three-dimensional seismic wave velocity models in Antarctica... more To improve the lateral resolution of three-dimensional seismic wave velocity models in Antarctica and the surrounding oceans, we have analysed direct earthquake-to-station Rayleigh-wave data observed on the vertical high-gain long-period and the very long period components of seven GEOSCOPE stations located in the southern hemisphere and three other stations at equatorial latitudes. The phase velocities of Rayleigh waves along 400 well-distributed paths are obtained in the period range 60-300 s, by fitting the data with synthetic seismograms computed with known source parameters in a reference earth model represented by the Preliminary Reference Earth Model (PREM). Corrections for shallow layers have been carefully applied to the observed phase velocities. The geographical distributions of phase velocities and azimuthal anisotropy are then computed with the tomographic method without any a priori regionalization developed by Montagner (Ann. Geophys., 4(B3): 283-294, 1986). The results show some new and important features of Antarctica and the southern hemisphere. The locations of velocity anomalies are well resolved. The eastern part of Antarctica corresponds to a craton-like structure down to depths of about 250 km, and the highest velocities are observed in Enderby Land, where some of the oldest rocks in the world have been sampled. The low velocities are located along the ridges encircling the Antarctic continent. The lowest velocities appear in some areas corresponding to hotspots (Crozet, Kerguelen, Macquarie and Balleny Islands). Also, an elongated low velocity is found on the western flank of the Transantarctic Mountains, which might be related to the existence of a rift zone similar to the African rift. The Australia-Antarctica Discordance (AAD) presents slow velocities near the surface but fast velocities below the lithosphere. These main features are discussed in the framework of the Gondwana hypothesis and the earlier supercontinent. The first azimuthal anisotropy results are also discussed. Anisotropy values are smaller within the Antarctic continent than in the surrounding oceans. They are also small in the AAD but particularly large in the areas around it, suggesting an active tectonic process characterized by a downward flow at depth, a good candidate for a cold spot or a new subduction zone.
Physics of the Earth and Planetary Interiors, 1999
Direct earthquake-to-station Rayleigh and Love wave data observed on high gain broadband records ... more Direct earthquake-to-station Rayleigh and Love wave data observed on high gain broadband records are analyzed in order to improve the lateral resolution of the uppermost mantle in the southwest Pacific region. We used data of nine permanent Geoscope and Iris stations located in the southern hemisphere and nine other stations as part of two temporary networks, the Ž .
Uploads
Papers by Geneviève roult