LAUSR

The large scale stress patterns observed in intra-plate areas are often considered to result from far-field boundary forces that drive plate tectonics. However, no present-day deformation has been detected in the French Paris Basin, yet significant deviatoric stresses are measured in limestone formations observed above soft argillite layers encountered in this region. Further, the pore pressure measured in the argillite is larger than that measured in the surrounding permeable zones. These observations suggest a presently active source of stress in this sedimentary system. We propose that this stress field is not related to tectonics but only to gravity acting on the series of visco-elastic orthotropic geomaterials that fill up the basin. This visco-elastic response is linked to pressure solution effects activated by pore pressure transients related to climatic variations. These pressure transients develop in the fracture system that affects some of the geomaterials and imply a time dependant deformation field, with time constants related to those of climatic variations. This model outlines the influence of time-dependent material properties on the present day stress and pore pressure fields that prevail at various depths. It may be considered as a possible loading mechanism for the analysis of intra-plate seismicity.