On the importance of setting 3-D stress field in simulations of on- and off-fault deformation

During the last decades, many numerical models have been developed to investigate the conditions for seismic and aseismic slip. Those models explore the behaviour of frictional faults, embedded in either elastic or inelastic media and submitted to a far field loading (seismic cycle models), or initial stresses (single dynamic rupture models). Those initial conditions impact both on-fault and off-fault dynamics. Because of the sparsity of direct measurements of fault stresses, modellers have to make assumptions about these initial conditions. To this day, Anderson's theory is the only framework that can be used to link fault generation and reactivation to the 3-D stress field. In this work, we look at the role of the 3-D stress field in modelling a 2-D strike-slip fault under plane-strain conditions. We show that setting up an incorrect initial stress field, based on Anderson's theory, can lead to underestimation of the damage zone width by up to a factor of six, for the studied cases. Moreover, because of the interactions between fault slip and off-fault deformation, initial stress field influences the rupture propagation. Our study emphasizes the need to set up the correct initial 3-D stress field, even in 2-D numerical simulations.