6 research outputs found
Evaluation of the new infrastructure for French Permanent BroadbandStations in Auvergne
International audienc
Characteristics and possible origins of the seismicity in northwestern France
International audienceThe macroseismic and instrumental observations accumulated by the Bureau Central Sismologique Français and other national agencies over the last 100 years show that the northwestern part of metropolitan France is affected by an apparently diffuse and moderate intraplate seismicity. Far from any plate boundary, well-documented inherited structures, such as the Armorican shear zone network, the Sillon Houiller, and the normal faults related to the Atlantic ocean margin, likely exert significant control on the regional seismicity pattern. However, in the absence of a clearly measurable strain field, processes other than far-field tectonic stress loading such as erosion, gravitational potential energy, and/or hydraulic loadings can co-exist, but their respective influence on the current seismicity is debated and remains to be fully addressed. Reliable detection/location of low-to-moderate magnitude events is one of the most important challenges in the near future to better understand the processes that control this intraplate seismicity. As shown here for a limited region, this issue can be achieved positively, thanks to the new RĂ©sif-Epos network, in conjunction with sophisticated algorithms for both earthquakesâ detection and discrimination
Amélioration de la qualité des stations permanentes françaises à large bande possédant des installations à forage peu profond
International audienceWithin the framework of the RĂ©sif (French seismological and geodetic network) research infrastructure, a major extension of the French permanent broadband network (RLBP) has been initiated in 2011 with the objective to reach ~190 stations by 2020. This network will allow a more homogeneous covering of metropolitan France, encompassing a wide variety of tectonic and geological units. Presently the RLBP network consists in 124 operating stations.For each new potential site a test was conducted for ~3 weeks, usually burying the broadband sensor at 50-80 cm depth directly in the ground or within a light temporary vault.For the final set-up, we tested various hosting infrastructures at three prototype sites and decided to promote the installation of a posthole sensor in a steel-cased shallow borehole, 5-20m deep, for all the sites in open areas. 43 stations have already been installed this way and have been operated for 5 to 20 months.RĂ©sif is a national research infrastructure dedicated to the observation and understanding of the structure and dynamics of the Internal Earth. RĂ©sif is based on high-tech observation networks, composed of seismological, geodetic and gravimetric instruments deployed in a dense manner throughout France. The data collected make it possible to study with high spatial and temporal resolution the deformation of the ground, surface and deep structures, seismicity on a local and global scale and natural hazards, and more particularly seismic events, on French territory. RĂ©sif is part of the European (EPOS - European Plate Observing System) and global systems of instruments used to image the Earth's interior as a whole and to study many natural phenomena.Dans le cadre des infrastructures de recherche du RĂ©sif (RĂ©seau sismologique et gĂ©odĂ©sique français), une extension majeure du rĂ©seau haut dĂ©bit permanent français (RLBP) a Ă©tĂ© initiĂ©e en 2011 avec pour objectif d'atteindre ~190 stations en 2020. Ce rĂ©seau permettra une couverture plus homogĂšne de la France mĂ©tropolitaine, englobant une grande variĂ©tĂ© d'unitĂ©s tectoniques et gĂ©ologiques. Actuellement, le rĂ©seau RLBP compte 124 stations opĂ©rationnelles.Pour chaque nouveau site potentiel, un test a Ă©tĂ© effectuĂ© pendant environ 3 semaines, gĂ©nĂ©ralement en enterrant le capteur large bande Ă une profondeur de 50 Ă 80 cm directement dans le sol ou dans une voĂ»te temporaire lĂ©gĂšre.Pour la mise en place finale, nous avons testĂ© diffĂ©rentes infrastructures d'hĂ©bergement sur trois sites prototypes et avons dĂ©cidĂ© de promouvoir l'installation d'un capteur dans un puits de forage peu profond, 5-20m de profondeur, en acier, pour tous les sites en zones ouvertes. 43 stations ont dĂ©jĂ Ă©tĂ© installĂ©es de cette façon et ont Ă©tĂ© exploitĂ©es pendant 5 Ă 20 mois.RĂ©sif est une infrastructure de recherche nationale dĂ©diĂ©e Ă lâobservation et la comprĂ©hension de la structure et de la dynamique Terre interne. RĂ©sif se base sur des rĂ©seaux dâobservation de haut niveau technologique, composĂ©s dâinstruments sismologiques, gĂ©odĂ©siques et gravimĂ©triques dĂ©ployĂ©s de maniĂšre dense sur tout le territoire français. Les donnĂ©es recueillies permettent dâĂ©tudier avec une haute rĂ©solution spatio-temporelle la dĂ©formation du sol, les structures superficielles et profondes, la sismicitĂ© Ă lâĂ©chelle locale et globale et les alĂ©as naturels, et plus particuliĂšrement sismiques, sur le territoire français. RĂ©sif sâintĂšgre aux dispositifs europĂ©ens (EPOS - European Plate Observing System) et mondiaux dâinstruments permettant dâimager lâintĂ©rieur de la Terre dans sa globalitĂ© et dâĂ©tudier de nombreux phĂ©nomĂšnes naturels