TRACKING EFFICIENCY ASSOCIATED WITH FAULT SYSTEM REORGANIZATION IN LABORATORY AND NUMERICAL EXPERIMENTS

Laboratory and numerical experiments demonstrate that fault evolution includes episodes of fault reorganization that optimize work on the fault system. Consequently, the mechanical and kinematic efficiency of fault systems do not increase monotonically through their evolution. New fault configurations can optimize the external work required to accommodate deformation, suggesting that changes in system efficiency can drive fault reorganization. Laboratory evidence and numerical results show that fault reorganization within accretion and strike-slip systems is associated with increasing efficiency due to increased fault slip (frictional work and seismic energy) and commensurate decreased off-fault deformation (internal work and work against gravity).

Between episodes of fault reorganization, fault systems may become less efficient as they produce increasing off fault deformation. For example, laboratory and numerical experiments show that the interference and interaction between different fault segments may increase local internal work or that increasing convergence can increase work against gravity produced by a fault system. This accumulation of work triggers fault reorganization. The internal work and work against gravity are conservative, so stored work produced in deforming the inefficient system provides the energy required to grow new faults that reorganize the system to a more efficient configuration.

The results of laboratory and numerical experiments reveal that we should expect crustal fault systems to reorganize following periods of increasing inefficiency, even in the absence of changes to the tectonic regime that loads the faults. The time frame of fault reorganization depends on fault system configuration, strain rate and processes that relax stresses within the crust. For example, stress relaxation may keep pace with stress accumulation, which limits the increase in the internal work and gravitational work so that irregularities can persist along active fault systems without reorganization of the fault system. Understanding the partitioning of the work budget through laboratory and numerical experiments can reveal the processes that govern fault reorganization to more optimal configurations.