Dissertation defence (Geology): FM Nicklas Nordbäck

FM Nicklas Nordbäck defends the dissertation in Geology titled “Characterisation of brittle structures of bedrock in southern Finland - Unravelling the evolution and properties of fault and fracture systems and their prediction at different scales” at the University of Turku on 10 May 2024 at 12.15 (University of Turku, Main Building, Säästöpankki lecture hall, Turku).

Opponent: Professor Uwe Ring (Stockholm University, Sweden)
Custos: Professor Antti Ojala (University of Turku)

Doctoral Dissertation at UTUPub: https://urn.fi/URN:ISBN:978-951-29-9695-7


Summary of the Doctoral Dissertation:

Fractures in our bedrock develop due to forces caused by plate tectonics that slowly move, tear apart and put together old and new continents around the Earth. This doctoral thesis focuses on the evolution and characteristics of fractures within the crystalline bedrock in southern Finland. To establish age relationships and gain understanding of the complex evolution of fracture networks occurring in the bedrock, the investigations included analysis of multiscale datasets ranging from traditional bedrock observations to drone photogrammetry and airborne datasets. In addition, isotopic age dating of fractured rock samples from the underground spent nuclear fuel repository in Olkiluoto provided additional time constraints.

The results provide new scientific findings regarding the age of fractures and give explanations for their formation. These results show that major fractured zones of the bedrock developed during a period between approximately 1.75 to 1.0 billion years ago, when the bedrock in southern Finland was affected by different stress states, due to the movement, collisions, and exhumation of continental plates. The majority of all fractures in the bedrock seem to have formed before 550 Ma when the current bedrock surface had become revealed to the surface of the Earth.

In addition to understanding the tectonic history of the bedrock, the scientific problems addressed in this thesis have significance for the modelling and understanding of the properties of fractured bedrock volumes and future stability. This is especially important in geological storage of spent nuclear fuel there is a need to gain a good understanding of the fracture systems and to predict their mechanical and seismic stability and hydrogeological properties for the next 100 000 years.
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