164 Seismic Imaging underground facilities (Andra, 2009). A 3D seismic survey (37 km2) was recorded to verify the geometry and properties of the clay formation and of the underlying and overlying limestone formations. In addition to the 3D seismic campaign, drilling and geophysical borehole measurements, including vertical seismic profiles (VSP), and up-hole investigations were performed to calibrate the 3D seismic blocks and to perform the time-to-depth conversion. After presenting the geological setting, we describe the survey design and the processing applied to the dataset. We describe a method that could be developed to build a geo-model in depth, using pre-stack time migration, elastic inversion in time and the relationship between P-wave velocity and acoustic impedance. We also show how petro-physical studies could be conducted. 2D and 3D lines are used to illustrate the potential of the proposed procedure for estimating density (ρ), velocity (Vp, Vs), distributions of mechanical (Q factor, dynamic and static moduli) and petro-physical parameters (porosity, specific surface, permeability indicator). This chapter is a review of published literature. The data and parameter values contained in this chapter do not predetermine the use that will be made of them for design and safety analyses. 7.1 Geological setting The Meuse/Haute-Marne sector is located in the eastern part of the Paris Basin (Figure 7.1). The sedimentary succession shows a simple, monocline structure, dipping towards the centre of the basin (NW) which follows the general structure of the basin. The sector north of the Haute-Marne and south of the Meuse (Figure 7.1) constitutes a geologically simple area of the Paris Basin, with a succession of layers of limestone, marl and clay rock deposited in ancient ocean. The dip of the layers is low, around 1° to 1.5° towards the north-west. The Callovo-Oxfordian formation was chosen to host the Cigéo underground installation. It comprises 155 million year old clay rock, which is at least 130 meters thick and located at a depth of between 400 and 600 meters. It is referred to herein as the Callovo-Oxfordian argillites (Cox) formation. The selection of this Callovo-Oxfordian formation was based on its depth, low permeability, weak diffusion of solutes, high retention capacities and its significant thickness, which is favourable to the limitation of radionuclide migration from the Callovo-Oxfordian, into the surrounding formations, and then the biosphere, for a time scale of at least several hundred thousand years. The top of the Cox formation is more carbonate-rich, with interbedded clayey layers and carbonate rock. The Cox is more homogeneous in its central part with a clay-mineral concentration of 45-50%, which corresponds to a maximum of flooding within the area. A detailed study of the spatial variability of the Cox geological and physical properties may be found in Garcia et al. (2011). This formation is
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