Options
Lelievre, Marjorie
Loading...
2 results
Now showing 1 - 2 of 2
- PublicationRestrictedThe GROSMarin experiment: three dimensional crustal structure of the North Ligurian margin from refraction tomography and preliminary analysis of microseismic measurements(2011)
; ; ; ; ; ; ; ; ; ; ; ; ;Dessa, J.-X.; Geoazur, Univ. P. et M. Curie, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Simon, S.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Lelievre, M.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Beslier, M.-O.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Deschamps, A.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Bethoux, N.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Solarino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Sage, F.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Eva, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Ferretti, G.; DipTeRis, Università degli Studi di Genova, Italy ;Bellier, O.; CEREGE, (CNRS UMR 6635, Univ. P. Cézanne Aix-Marseille, IRD, Collège de France), Europole Méditerranéen de l’Arbois, BP 80, 13545 Aix-en-Provence, France ;Eva, C.; DipTeRis, Università degli Studi di Genova, Italy; ; ; ; ; ; ; ; ; ; ; The deep structure of the North Ligurian margin and its contiguous Ligurian basin as well as the seismicity recorded in these zones are neither well understood nor precisely constrained. In order to better address these questions, there is a need for offshore instrumenting, which was realised for a duration of nearly 6 months during the GROSMarin (Grand Réseau d’Observation Sous-Marin) experiment. An array of 21 ocean bottom seismometers was deployed over the most active area of the margin and was complemented on land by mobile seismological stations that densified existing permanent networks. We also realised the acquisition of deep refraction seismic shots at sea in order to get a 3D distribution of velocities along the margin through travel time tomography. We present here a preliminary analysis of the seismicity recorded during this experiment and a tomographic model of the margin structures obtained using data from the offshore network only. Our results support the existence of a high velocity zone at the base of a domain interpreted as transitional between continental and oceanic ones, on the northern part of the deep basin. A very similar pattern is observed across the neighbouring margin of the Gulf of Lions and is most likely related to serpentinisation of the underlying mantle during late rifting and continental break-up. North of this transition zone, we observe the basinward crustal thinning of the continental crust beneath the margin that seemingly narrows eastward. To the south, our results hint at transition to the oceanic domain. In contrast, our velocity distribution does not reveal a transition along strike between transitional and oceanic domains, as previous works suggest. Some microseismic activity was recorded throughout the duration of the experiment, on land and at sea. The number of detected events and precision of location were both improved by our considering French and Italian permanent networks. The detection capabilities of our dense network still need to be fully exploited269 32 - PublicationOpen Access3D Crustal Structure of the North-Ligurian Margin: First Results of the GROSMarin Experiment(2010)
; ; ; ; ; ; ;GROSMARIN TEAM ;Dessa, Jean-Xavier; UPMC/OCA/UNS/INSU-CNRS/IRD ;Lelievre, Marjorie; UPMC/OCA/UNS/INSU-CNRS/IRD ;Simon, Soazig; UPMC/OCA/UNS/INSU-CNRS/IRD ;Deschamps, Anne; UPMC/OCA/UNS/INSU-CNRS/IRD ;Béthoux, Nicole; UPMC/OCA/UNS/INSU-CNRS/IRD ;Solarino, Stefano; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;GROSMARIN TEAM; ; ; ; ; ; The North-Ligurian rifted margin is singular in that it lies immediately next to the Alpine orogenic arc. It is furthermore seismically active and can experience destructive earthquakes such as in 1887 in the region of Imperia—an event that resulted in a tsunami and more than 600 casualties in spite of a coastal area that was much less densely populated than today. Out of such rare large events, the area undergoes a limited and diffuse seismic activity that can remain undetected and is generally poorly located. This results in a poor knowledge of active structures, especially at sea. Such knowledge is however required towards a quantification of the seismic hazard along the French Riviera and the Ligurian region. To this end, the GROSMarin project was undertaken with a dual objective: (1) to characterize the North-Ligurian margin from a structural standpoint—mode and degree of crustal stretching prior to oceanic accretion, segmentation along strike, subsequent evolution in an orogenic context— and (2) to identify zones of active crustal deformation at sea that are likely to generate earthquakes. The programme is a collaborative work between GeoAzur and Dip.Te.Ris (University of Genova), with some support from INGV, IFM-GEOMAR and IFREMER. It took place from April to October 2008 and consisted in the deployment of 21 ocean-bottom seismometers (OBS) on a grid spanning 50 km along strike and 25 km across, located between Nice, France, and Imperia, Italy, and ranging from mid-slope to the deep basin. This array was extended on land by the permanent stations of the French and Italian regional networks, temporarily densified by 13 portable stations. These instruments recorded the shots of a marine seismic source towed from R/V l’Atalante and were left for more than 5 months for passive surveying. The active part of the programme aims at characterizing the main structures of the margin through crustal 3D tomography; the objective of the passive part is to decrease the detection threshold of marine microseismicity and to reach a precise location of events in order to map active faults. Some of the sea and land instruments were fitted with broadband sensors to allow for teleseismic imaging of deep lithospheric discontinuities. We present the preliminary results of this experiment—in particular a first 3D tomographic model obtained from 31.500 travel times derived from our recording of active seismic shots by the OBS’s. Passive data analysis is being under progress and first relocations have been obtained. These results give an insight into the variability of the crustal structure, both along and across strike.177 80