This report presents a pilot study in which the relative movements of major rejections in the Stockholm area have been investigated. Then, rock stress directions are estimated by analyzing the movement data using a theory called ”stress inversion” as well as numerical modeling.

Methods based on the theory of stress inversion have previously been used in Forsmark, Laxemar-Simpevarp and Olkiluoto (Sanitot et al., 2011, Viola et al., 2009, Viola et al., 2011), where different stress fields could be identified in different geological periods.

In the framework of this project, mapping of fractures with movement indicators has been performed in 6 different locations in the Stockholm area. The relative movements are identified from striations on fracture surfaces as well as displacement of intersecting structures, such as dykes. Totally, data on 46 fracture surfaces have been obtained.

The movement data can then be analyzed and the rock stress directions obtained by using the computer program ”Tensor”. The ”stress inversion” theory is used in the computer program. An important assumption for the ”stress inversion” theory is that the direction of the movement on a fracture is parallel with the largest shear stress on the fracture surface.

Appendices 1 & 2 belong to the report and can be opened or downloaded