InSight: Single Station Broadband Seismology for Probing Mars' Interior

InSight is a proposed Discovery mission which will deliver a lander containing geophysical instrumentation, including a heat flow probe and a seismometer package, to Mars. The aim of this mission is to perform, for the first time, an in-situ investigation of the interior of a truly Earth- like planet other than our own, with the goal of understanding the formation and evolution of terrestrial planets through investigation of the interior structure and processes of Mars

Mantle upwellings and convective instabilities revealed by seismic tomography and helium isotope geochemistry beneath eastern Africa

International audienceThe relationship between intraplate volcanism and continental tectonics has been investigated for North and East Africa using a high resolution three-dimensional anisotropic tomographic model derived from seismic data of a French experiment ''Horn of Africa'' and existing broadband data. The joint inversion for seismic velocity and anisotropy of the upper 400 km of the mantle, and geochemical data reveals a complex interaction between mantle upwellings, and lithosphere. Two kinds of mantle upwellings can be distinguished: The first one, the Afar ''plume'' originates from deeper than 400 km and is characterized by enrichment in primordial 3 He and 3 He/ 4 He ratios higher than those along mid-ocean ridges (MOR). The second one, associated with other Cenozoic volcanic provinces (Darfur, Tibesti, Hoggar, Cameroon), with 3 He/ 4 He ratios similar to, or lower than MOR, is a consequence of shallower upwelling. The presumed asthenospheric convective instabilities are oriented in an east-west direction, resulting from interaction between south-north asthenospheric mantle flow, main plume head and topography on the base of lithosphere

High-resolution imaging of the Pyrenees and Massif Central from the data of the PYROPE and IBERARRAY portable array deployments

International audienceThe lithospheric structures beneath the Pyrenees, which holds the key to settle long-standing controversies regarding the opening of the Bay of Biscay and the formation of the Pyrenees, are still poorly known. The temporary PYROPE and IBERARRAY experiments have recently filled a strong deficit of seismological stations in this part of western Europe, offering a new and unique opportunity to image crustal and mantle structures with unprecedented resolution. Here we report the results of the first tomographic study of the Pyrenees relying on this rich data set. The important aspects of our tomographic study are the precision of both absolute and relative traveltime measurements obtained by a nonlinear simulated annealing waveform fit and the detailed crustal model that has been constructed to compute accurate crustal corrections. Beneath the Massif Central, the most prominent feature is a widespread slow anomaly that reflects a strong thermal anomaly resulting from the thinning of the lithosphere and upwelling of the asthenosphere. Our tomographic images clearly exclude scenarios involving subduction of oceanic lithosphere beneath the Pyrenees. In contrast, they reveal the segmentation of lithospheric structures, mainly by two major lithospheric faults, the Toulouse fault in the central Pyrenees and the Pamplona fault in the western Pyrenees. These inherited Hercynian faults were reactivated during the Cretaceous rifting of the Aquitaine and Iberian margins and during the Cenozoic Alpine convergence. Therefore, the Pyrenees can be seen as resulting from the tectonic inversion of a segmented continental rift that was buried by subduction beneath the European plate

Planned Products of the Mars Structure Service for the InSight Mission to Mars

Abstract The InSight lander will deliver geophysical instruments to Mars in 2018, including seismometers installed directly on the surface (Seismic Experiment for Interior Structure, SEIS). Routine operations will be split into two services, the Mars Structure Service(MSS) and Marsquake Service (MQS), which will be responsible, respectively, for defining the structure models and seismicity catalogs from the mission. The MSS will deliver a series of products before the landing, during the operations, and finally to the Planetary Data System (PDS) archive. Prior to the mission, we assembled a suite of a priori models of Mars, based on estimates of bulk composition and thermal profiles. Initial models during the mission will rely on modeling surface waves and impact-generated body waves independent of prior knowledge of structure. Later modeling will include simultaneous inversion of seismic observations for source and structural parameters. We use Bayesian inversion techniques to obtain robust probability distribution functions of interior structure parameters. Shallow structure will be characterized using the hammering of the heatflow probe mole, as well as measurements of surface wave ellipticity. Crustal scale structure will be constrained by measurements of receiver function and broadband Rayleigh wave ellipticity measurements. Core interacting body wave phases should be observable above modeled martian noise levels, allowing us to constrain deep structure. Normal modes of Mars should also be observable and can be used to estimate the globally averaged 1D structure, while combination with results from the InSight radio science mission and orbital observations will allow for constraint of deeper structure

Dernière campagne de forages du projet Construction large bande

National audienceGouttières (27), Restinclières (34), Champagny-en-Vanoise (73), Gouzon (23), Béthincourt (55), Méricourt (80)... Voici là un petit aperçu des 12 étapes du "tour de France des forages" de l'année 2020

Dernière campagne de forages du projet Construction large bande

National audienceGouttières (27), Restinclières (34), Champagny-en-Vanoise (73), Gouzon (23), Béthincourt (55), Méricourt (80)... Voici là un petit aperçu des 12 étapes du "tour de France des forages" de l'année 2020

Dernière campagne de forages du projet Construction large bande

National audienceGouttières (27), Restinclières (34), Champagny-en-Vanoise (73), Gouzon (23), Béthincourt (55), Méricourt (80)... Voici là un petit aperçu des 12 étapes du "tour de France des forages" de l'année 2020

The Snake River Plain Experiment revisited. Relationships between a Farallon plate fragment and the transition zone

International audienceWe reconsider the analysis of the 93 PASSCAL-OREGON SRP experiment data. The techniques applied to the processing of Pds waves, which are P to $ conversions at seismic discontinuities at depth d in the receiver region, differ from those employed by Ducker & S/•ee/•an [1997]. We perform global moveout corrections and migration, taking advantage of the alignment of seismicity along the great circle described by the array (South America, and the Kuril and Aleutians islands). We do not detect a deep signature of a mantle plume. The 410 km discontinuity exhibits a fragmented aspect, which prevents us from reliably estimating the transition zone thickness. The 660 km discontinuity is clearly more visible, and largely deflected in a large part of the profile. We associate this anomalous behaviour and the noisy aspect of the discontinuities with the presence of a Farallon plate fragment. 660 have been reported on a regional scale study using an array of 20 broadband stations in the Yellowstone-Snake River Plain (YSRP) complex [Ducker & S/•ee-/•an, 1997]. The array configuration was a 510 km NW-SE trending line crossing the YSRP (Fig. 1), which is assumed to be the Yellowstone hotspot track [Smith & Braile, 1994]. Indeed, while a part of the magmatic material is trapped in the lithosphere under the actual Yellowstone caldera, producing high siliceous lavas, the plume is sheared by the North-American plate motion. We analyze the data produced by the 93 PASSCAL-OREGON SR

Anisotropic structure of the African upper mantle from Rayleigh and Love wave tomography

International audienceThe geodynamics of the mantle below Africa is not well understood and anisotropy tomography can provide new insight into the coupling between the African plate and the underlying mantle convection. In order to study the anisotropic structure of the upper mantle beneath Africa, we have measured phase velocities of 2900 Rayleigh and 1050 Love waves using the roller-coaster algorithm [Beucler, E., Stutzmann, E., Montagner, J.-P., 2003. Surface-wave higher mode phase velocity measurments, using a roller-coaster type algorithm. Geophys. J. Int. 155 (1), 289–307]. These phase velocities have been inverted to obtain a new tomographic model that gives access to isotropic SV-wave velocity perturbations, azimuthal and radial anisotropies. Isotropic SV-wave velocity maps have a lateral resolution of 500 km. Anisotropy parameters have a lateral resolution of 1000 km which is uniform over Africa for azimuthal anisotropy but decreases at the West and South of Africa for radial anisotropy. At shallow depth, azimuthal anisotropy varies over horizontal distances much smaller than the continent scale. At 280 km depth, azimuthal anisotropy is roughly N-S, except in the Afar area, which might indicate differential motion between the African plate and the underlying mantle. The three cratons of West Africa, Congo and Kalahari are associated with fast velocities and transverse anisotropy that decrease very gradually down to 300 km depth. On the other hand, we observe a significant change in the direction and amplitude of azimuthal anisotropy at about 180 km depth, which could be the signature of the root of these cratons. The Tanzania craton is a shallower structure than the other African cratons and the slow velocities (−2%) observed on the maps at 180 and 280 km depth could be the signature of hot material such as a plume head below the craton. This slow velocity anomaly extends toward the Afar and azimuthal anisotropy fast directions are N-S at 180 km depth, indicating a possible interaction between the Tanzania small plume and the Afar. The Afar plume is associated with a very slow velocity anomaly (−6%) which extens below the Red sea, the Gulf of Aden and the Ethiopian rift at 80 km depth. The Afar plume can be observed down to our deepest depth (300 km) and is associated with radial anisotropy smaller than elsewhere in Africa, suggesting active upwelling. Azimuthal anisotropy directions change with increasing depth, being N-S below the Red sea and Gulf of Aden at 80 km depth and E–W to NE–SW at 180 km depth. The Afar plume is not connected with the smaller hotspots of Central Africa, which are associated either with shallow slow velocities for Mt Cameroon or with no particular velocity anomaly and N-S azimuthal anisotropy for the hotspots of Tibesti, Darfur and Hoggar. A shallow origin for these hotspots is in agreement with their normal 3He/4He ratio and with their location in a region that had been weakened by the rifting of West and Central Africa

Feedback on the installation of a borehole broadband seismometer at station BOUF, French permanent broadband network

International audienceThe French permanent broadband network (RLBP) is planned to develop in Brittany, NW France, in the following year. This region mostly lies on the Armorican Massif – a peneplained remnant of the Hercynian orogen – where almost no cave exists and where human presence is widespread due to intense agriculture activities. For those two reasons, choice has be made to install the broadband sensor of the future seismological stations into 10 m deep cased boreholes. Our first realization is the BOUF station, located at Bouguenais at c.a 15 km south from Nantes, France. This site was previously instrumented for 3 years during the PyrOPE temporary deployment with a 1 m deep seismic vault. The first 6 months of measurements in the borehole shows a dramatical decrease of the seismic noise (∼10 dB) above 20 s of period compared with the previous installation. We however stress that great care should be taken during the putting in of the sensor, and in particular on the cable configuration. We propose here some indications and good practice to achieve a good quality measuring site. We also present here the results of a set of tests we performed on the structure of the borehole: diagraphy analyses, check of the welds and of the concrete, temperature profile