UMR Geoazur

Valbonne, France

UMR Geoazur

Valbonne, France
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Bensalah M.K.,Cadi Ayyad University | Bensalah M.K.,University of Lisbon | Youbi N.,Cadi Ayyad University | Youbi N.,University of Lisbon | And 17 more authors.
Journal of African Earth Sciences | Year: 2015

We welcome the comment by Michard et al. (2013) as it gives us the opportunity to better discuss the Jurassic-Cretaceous magmatism of the High Atlas (Morocco). In their comment, Michard et al. (2013) focus on three main points which are: (i) the age of the basalts from Naour, (ii) the structural history of the Central High Atlas and (iii) the geodynamic significance of the related Jurassic-Cretaceous magmatism. We will address these questions in the following sections. © 2015 Elsevier Ltd.

Bensalah M.K.,Cadi Ayyad University | Bensalah M.K.,University of Lisbon | Youbi N.,Cadi Ayyad University | Youbi N.,University of Lisbon | And 19 more authors.
Journal of African Earth Sciences | Year: 2013

Basaltic lava flows, dykes and sills, interbedded within red clastic continental sedimentary sequences (the so called " Couches Rouges" ) are widespread in the Oued El-Abid syncline. They represent the best candidates to study the Jurassic-Cretaceous magmatism in the Moroccan High Atlas. The volcanic successions were formed during two pulses of volcanic activity, represented by the Middle to Upper Jurassic basaltic sequence B1 (1-4 eruptions) and the Lower Cretaceous basaltic sequence B2 (three eruptions). Whether belonging to the B1 or B2, the lava flows present morphology and internal structures typical of inflated pahoehoe. Our geochemical data show that, at least for Jurassic magmatism, the dykes, and sills cannot be considered as strictly representing the feeders of the sampled lava flows. The Middle to Upper Jurassic pulse is moderately alkaline in character, while the Lower Cretaceous one is transitional. Crustal contamination plays a minor role in the petrogenesis of these magmas, which were generated by variable partial melting degrees of a garnet-bearing mantle source. Magmatism location was controlled by pre-existing Hercynian fault systems reactivated during a Middle to Upper Jurassic-Cretaceous rifting event. The associated lithospheric stretching induced melting, by adiabatic decompression, of enriched low-solidus infra-lithospheric domains. © 2013 Elsevier Ltd.

Cociani L.,University College Dublin | Bean C.J.,University College Dublin | Lyon-Caen H.,Ecole Normale Superieure de Paris | Pacchiani F.,National Institute of Oceanography and Applied Geophysics - OGS | Deschamps A.,UMR Geoazur
Journal of Geophysical Research: Solid Earth | Year: 2010

The analysis of temporal variations in the seismic velocity across faults can be used to estimate in situ stress changes. Seismic velocity of propagation depends on the fault stiffness, which is a function of stress. The coda wave interferometry technique is applied to seven families of repeating earthquakes (multiplets) recorded on the southern shore of the Gulf of Corinth, Greece, to estimate high precision velocity changes in the Earth's crust associated with the Mw = 4.3 Agios Ioanis earthquake. Results show that the Agios Ioanis event causes a perturbation in elastic properties at seismogenic depth, resulting in a reduction of 0.2% in the seismic velocity. The results are not consistent with either damage induced by dynamic stresses nor a fluid transient origin. In contrast, both the spatial distribution and magnitude of the velocity perturbation correlate well with modeled static stress variations. This suggests that the measured changes in the mechanical properties of the seismogenic crust can be attributed to a change in static stress field associated with the Mw = 4.3 Agios Ioanis earthquake. The velocity changes indicate an unclamping of the Pyrgaki fault at depth, which has local hazard implications. Copyright 2010 by the American Geophysical Union.

Malinowski M.,Institute of Geophysics PAS | Operto S.,UMR Geoazur | Ribodetti A.,UMR Geoazur
73rd European Association of Geoscientists and Engineers Conference and Exhibition 2011: Unconventional Resources and the Role of Technology. Incorporating SPE EUROPEC 2011 | Year: 2011

Here we assess the potential of the visco-acoustic frequency domain full-waveform inversion (FWI) to reconstruct P-wave velocity and P-wave attenuation factor (Qp) from onshore seismic data. We show that both the velocity and the attenuation factor can be reliably reconstructed with a comparable resolution and without trade-off for sufficiently attenuating media and sufficiently-accurate velocity starting model by non-linear inversion. We applied both the acoustic and visco-acoustic FWI to real wide-aperture onshore seismic data with a strong footprint of attenuation that were recorded in the Polish Basin. We show how a heuristic normalisation of the data with offset allows us to remove the effect of the attenuation from the data and reconstruct a reliable velocity model in the acoustic approximation. Alternatively, visco-acoustic FWI allows us to reconstruct jointly both a reliable velocity model and a Q model from the true-amplitude data. We find the recovered velocity and Q models consistent with the expected lithology and stratigraphy in the study area. We link high-attenuation zones with the increased clay content and the presence of the mineralized fluids.

Belli A.,UMR Geoazur | Belli A.,University of Franche Comte | Exertier P.,UMR Geoazur | Samain E.,UMR Geoazur | And 4 more authors.
Advances in Space Research | Year: 2015

The Time Transfer by Laser Link (T2L2) experiment on-board the Jason-2 satellite was launched in June 2008 at 1335km altitude. It has been designed to use the Satellite Laser Ranging (SLR) space technique as an optical link between ground and space clocks. T2L2, as all the instruments aboard Jason-2, is referenced to the Ultra Stable Oscillator (USO) provided by the Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) system. A complex data processing has been developed in order to extract time & frequency products as the relative frequency bias of the USO from ground-to-space time transfer passages. The precision of these products was estimated of a few parts in 10-13 given the very good in-flight performance of T2L2 with a ground-to-space time stability of a few picoseconds (ps) over 100s. Frequency bias from T2L2 were compared with results from operational orbit computation, notably with the DIODE (Détermination Immédiate d'Orbite par Doris Embarqué) outputs (see Jayles et al. (2016) same issue) at the level of 1·10-12.The present paper is focusing on the main physical effects which drive the frequency variations of the Jason-2 USO during its flight, notably over the South Atlantic Anomaly (SAA) area. In addition to the effects of radiation we studied the effect of the residual temperature variations, in the range 8-11°C (measured on-board). A model was established to represent these effects on the short term with empirical coefficients (sensitivities of the USO) to be adjusted. The results of fitting the model over ∼200 10-day periods, from 2008 to 2014, show the sensitivities of the Jason-2 USO to temperature and radiation. The analysis of the 6-year output series of empirical coefficients allows us to conclude that: (i) the temperature to frequency dependence is very stable along time at the level of around -1.2·10-12 per°C, (ii) the radiation effects are much lower than those previously detected on the Jason-1 USO with a factor>10. The swept material used by manufacturers for the Jason-2 quartz oscillator has such properties to avoid non-linear effects >1-2·10-12, (iii) the model is available at 1min or less over the Jason-2 mission, with a level of consistency of 5·10-13, which is the average RMS of the post-fit residuals. © 2015 COSPAR.

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