Impact of Heterogeneous Initial Stress on the Seismic Cycle and Rupture Dynamics of a Long Laboratory Fault

Natural fault systems exhibit a complex interplay of factors that govern the nucleation, propagation, and arrest of ruptures. Among these factors, the distribution of initial stress stands out as a key driver of rupture dynamics, influencing the size, recurrence interval, and spatial characteristics of seismic events. The fault system size further contributes to the complexity of the seismic cycle. This study investigates how heterogeneous initial stress conditions shape the seismic cycle of a long experimental fault.We reproduce frictional ruptures on a biaxial direct shear apparatus hosting a 2.5 m long fault composed of analog material (PMMA). The initial stress distribution is controlled through a stopper that modifies the boundary conditions. Strain gauge rosettes, recording at 40 kHz, measure stress evolution.Our results demonstrate that stress heterogeneity significantly affects seismic behavior, including nucleation location and complexity of the seismic sequences (from system size events to supercycles). Moreover, stress heterogeneity strongly influences the dynamics of main ruptures, leading to complex behaviors such as temporary arrest and re-nucleation of the rupture. Time delays (time intervals between arrest and re-nucleation) were found to span two orders of magnitude and were significantly larger than the dynamic propagation period. Numerical simulations corroborate these findings, revealing delayed triggering mechanisms such as creeping front-induced, dynamic wave-induced, or a combination of the two.This study offers a framework for interpreting stress heterogeneity's spatial and temporal evolution along natural faults and its implications for earthquake predictability and rupture dynamics.