Vertical stress profiles and the significance of "stress decoupling"

Precise determinations of the complete stress tensor have been conducted at various depths near the village of Bure, in the eastern part of the Paris sedimentary Basin. They show that the magnitude of the principal stress components do not vary linearly with depth for this site. Similarly, precise data on the variation with depth of the maximum horizontal principal stress orientation, both in the southern Rhine Graben and in the North German Basin, show significant rotations. Vertical variations are controlled by the rheological characteristics and the relative thickness of the various formations. Hence the stress field observed at shallow depths in sedimentary formations may be decoupled from that which prevails at greater depth. It is proposed that in domains of very slow deformation rates, local deformation processes possibly associated with rock fluid interactions, but also with diapirism, may influence more significantly the local stress field than does the regional tectonic activity. Further, because principal stress directions have been found to rotate with depth both in sedimentary rocks as well as in crystalline and metamorphic domains down to depths much larger than those associated with topographic effects, it is concluded that large scale stress field analyses must take into account depths at which the various data have been collected. (C) 2012 Elsevier B.V. All rights reserved.