Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

324 PATA Days 2024 C O N C L U S I O N S Fig. 3 shows the assumed difference between rock masses in the 3DEC versus PFC codes. In 3DEC the rock mass is modeled as mainly intact and homogenous rock, interrupted only by thin “clean” fracture contacts. This is a good description of the repository volume at Forsmark in sparsely fractured igneous rock. In PFC the rock mass is represented by many rigid particles with limited edge contacts. This rock geometry better represents shear zones, composed of a crushed and shattered fault core with flanking damage zones (i.e., standard fault architecture). Given these differences, it is not surprising that displacements predicted by 3DEC are much smaller than those observed in historical DFs, if those DFs represent reactivated of shear zones, rather than of simple fractures. A C K N O W L E D G E M E N T S Carl-Henrik Pettersson of the Swedish Radiation Safety Authority commissioned this study andmade insightful comments. I gratefully acknowledge discussions on Fennoscandian postglacial faulting with Hilmar Bungum (Geological Survey of Norway), Colby Smith (Geological Survey of Sweden) and Raimo Sutinen (Geological Survey of Finland). Alexandra Sarmiento assisted me in navigating the FDHI database. Fig. 3: Representations of rock geometry assumed by 3DEC (left) versus PFC (right). From ITASCA (itascacg.com/software/distinct- element-method)