2012:52 Technical Note, Shear movement of near-field rock due to large earthquakes

The review assignment concentrates on the possible impact of large earthquakes on the shear deformation of large fractures in the repository volume. For this purpose a general review of some of SKB‘s top-level reports was carried out.

The reports draw a generally consistent and to a considerable extend comprehensive picture of the potential impact on the repository integrity in case of the unlikely event of a large earthquake close to the repository. The reports mostly include the relevant references and data. The conclusions drawn from the incorporated data is sound and consistent.

The analysis clearly shows that an earthquake, which could potentially influence the performance of the repository needs, to be very close to the repository and needs to be of considerable magnitude. In addition, such a seismic event can only have an impact, if large fractures that intersect canister positions are overlooked.

This review identifies two main areas that require additional analysis to gain stronger confidence in the concept. The stress field and stress evolution model for the repository area needs to be better understood, and the growth of fractures should be considered.

The stress measurements that have been performed at Forsmark leave room for discussion, and as the stress field is the starting point for any further geomechanical analysis, the stress field interpretation needs to be independently revisited.