The weakness of earthquake faults

Numerical experiments using the particle based lattice solid model produce simulated earthquakes. Model faults with a thin gouge layer are sufficiently weak relative to those without gouge to explain the heat flow paradox (HFP). Stress drop statistics are in agreement with field estimates. Models with a thick granular fault zone exhibit a strong evolution effect. Results are initially similar to those of laboratory experiments but after a sufficient time, the system self-organizes into a weak state. The long time required for self-organization could explain why weak gouge has not been observed in the laboratory. The new results suggest an HFP explanation without the so called 'fatal flaws' of previously proposed solutions. They demonstrate that fault friction potentially undergoes a strong evolution effect and could be dependent on gouge microstructure. This raises questions about the extent to which laboratory derived 'friction laws' can be used in macroscopic domain earthquake simulation studies.