Laboratory of Geodynamics and Geophysics (LGG)

• Mandat de l'équipe "géodynamique"
• Mandat de l'équipe "imagerie sismique"
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The technological developments achieved through seismic survey conducted over the last years have provided Ifremer with hight-performance equipment and tools. Priority is hanceforth given to processing and analysis methods that promote the development of tools which best enhance scientific data.

Collaboration between the different actors of the Institute working in the field the seismic imagery was thus created within the Department of Marine Geosciences with the aim of reaching the critical mass necessary to conduct projects and to improve the legibiliy of actions in this domain. The creation of a "seismic imagery" unit, within the Laboratory of Geophysics and Geodynamics of the department has been proposed. Consequently, the LGG is restructured into two groups, respectively "Geodynamics" and "Seismic Imagery", whose main assigments are defines below.

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Main assigments of the "Geodynamics" group

For the moment, the work of this group is concentrated around 3 main axes but a scientific watch is however insured on more various subjects, susceptible to feature in current events of the feature.

Axis 1 : Passive margins and sedimentary basins

The "Geodynamics" group leads a general scientific reflexion on passive margins which should result in a typology and a production of a training model of interest to the petroleum industry, among others.

Cette démarche holistique s’appuie sur des études de détails (campagnes à la mer, analyse structurale, analyse sédimentaire et modélisation numérique et analogique) intégrées dans des études globales (grandes synthèses) intégrant l’héritage tectonique, la géodynamique générale et régionale, la naissance des océans, la segmentation des bassins, les mouvements verticaux, la topographie (et l’érosion) des continents et l’influence de la segmentation mantellique.

Cet axe nécessite la continuation de la forte collaboration du Laboratoire avec l’industrie pétrolière (Petrobras, Total, Melrose, Statoil…) et d’autres institutions internationales (BGR…).

Axe 2 : Marges actives et risques naturels

Cet axe comprend deux aspects :

• L’enregistrement rapide des répliques des grands séismes, dans le but de mieux comprendre les mécanismes de ces événements.
• Un effort de plus long terme visant à mieux appréhender le fonctionnement des failles actives et de tenter d’évaluer l’aléa sismique associé.

Les principales méthodes utilisées dans cette approche sont :

• L'étude des séismes à plusieurs échelles (microséismes, répliques des grand séismes et fonctionnement du choc principal).
• Le rapport entre les fluides, le dégazage et l'activité des failles.
• La reconnaissance des failles actives par la sismique à différentes résolutions (de la très haute résolution jusqu'à la sismique).

Axis 3 : Geological fluids and ecosystems

The study of interactions between fluids and the substratum the source of oceanic ecosystems field implies geology and geodynamics. The participation of the LGG covers several aspects :

• The geological characterization of oceanic fluid exchange in particular the study of fluid exits on the major chimio-synthetic ecosystems in extreme conditions.
• The characterization of gas emissions associated with these exchangesmaking up the total carbon result.
• The study of the role of fluids in geological fluctuatin (slope instability, earthquakes, gas hydrate destabilizaion, etc.).

Mandate of the

« seismic imagery » group

Three axes are proposed :

Axis 1 : Geophysical research:

Pursual of methodological development for imagery and the geophysical characterization of geological processes.

This axes includes :

• proposing and leading research projects within the framework of Ifremer's main research programmes.
• participating in the assembly and running of research projects in geosciences.
• development end application of advanced processing methods.
• article publication.

On the technological level, the actions in progress - enumeral hereafter - will be carried out with the support of the RDT department. These actions are :

• SYSIF : multi-track component of deep towed seismic.
• GEOPS : Vp, Vs in situ measurements.
• Control of seismic sources for data exploitation.

Axis 2 : Support of the use of conventional geophysical methods :

This support intervenes at two levels :

"Prelimary draft" phase, to wich the Seismic Imagery group provides expert testimony for the definition of the geographysical means (technical and human) to be applied within the frame of a given scientific problematic. The possible implication of the laboratory, in the fields of data acquisition and processing related to a gven project will be discussed during this phase.

The "project" phase itself, includes one or more of the following tasks :

• direct or indirect participation, in the acquisition of geophysical data.
• implementation, maintenance and evolution of the software requirements for the "conventional" data processing of geophysical sea surveys.
• Training of students/personnel in the standard methods of processing.

Data processing is a perennial service which must reply to the demands of the department in this field. The support of the information technology department of the Instituteis also required in order to set up the adequate processing means (material, network architecture, optimized environment for the software employed) and to ensure their maintenance and evolution.

Axis 3 : Quality control of seismic data :

Initiated by the department NSE/AS, the action aimed at setting up methods of Quality Control of seismic data (HR, SISRAP, SMT) within the frame of IFREMER's mandate of common equipment stock management. It has resulted in the development of methods and software tools for quality control their availability to partners and the training of scientific users.

Recognized results of this action within the Marine Geoscience department (GO, BOBGEO, SIGOLO, Marmesonet, SESAME, SPIRAL…) and of several other French research laboratories (GéoSciences Azur, IUEM, IPGP) result in proposing the continuation of this work bound for scientific users.

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ESSES

Ifremer - Géosciences marines
B.P. 70 - 29280 Plouzané cédex, France
Fax building 611 : (33) 98.22.45.49 building 612 : (33) 98.22.45.70

Phone numbers:
* switchboard : (33) 98.22.40.40 or (33) 98.22 - Followed by extension number
* Secretarial department GM : 42.24

e-mail : Firstname.Name@ifremer.fr

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