Natural variability of fault friction and slip uncertainty exist in the
Earth's crust. To what extent it influences crustal stress and its
evolution is intriguing. We established a quasi-static, 2D model to
simulate the stress evolution due to Coulomb frictional slips in the
brittle crust. The model simply features randomly-oriented fractures
with heterogeneous frictional coefficients. We emphasized the global
stress response by summing the contribution of cascades of local
frictional slip under specific boundary conditions. We illustrated that
the decrease in stress difference manifests as a self-organized process
that ultimately leads to frictional equilibrium. The model informs that
the frictional equilibrium of a stochastic system can depart
substantially from a deterministic estimation. Although the model
quantitatively corroborates the notion of frictional equilibrium in
places where fracture slip is the dominant mechanism for stress release,
it reveals far more profound influence of system heterogeneity on the
local and global stress evolution.