Reactivation of Non‐Optimally Orientated Faults Due to Glacially Induced Stresses

Abstract The deformation due to an ice load is accompanied by displacement and stress changes. These stress changes are known to have created large‐magnitude earthquakes along pre‐existing faults during and after deglaciation of the Late Quaternary ice sheets. However, these so‐called glacially induced faults have been found to be not optimally orientated in their respective regional stress regime. Here, we analyzed the potential of non‐optimally orientated fault reactivation within a glacially induced stress field as well as changes of the stress regimes due to these additional stresses. A finite element model is used to estimate glacially induced stresses, which are then combined with background stress magnitudes. Non‐optimally orientated faults can be reactivated by glacially induced stresses within thrust‐, strike‐slip‐, and normal‐faulting stress regimes, but depending on their location with respect to the ice sheet and their orientation within the regional stress field. While faults with large variations of dip and strike outside of the ice sheet are prone to reactivation when the background stress field is a normal‐ or strike‐slip‐faulting stress regime, faults within a thrust‐faulting stress regime can also be reactivated within the ice margin during and after the deglaciation. Outside the ice margin, instabilities in a thrust‐faulting stress regime develop along the intermediate principal stress axis. Stress regime changes can occur for all background stress states. Finally, we find that certain conditions in a strike‐slip‐faulting stress regime can also explain the observed glacially induced thrust faults in Northern Europe.