Earthquake recurrence-time variations with and without fault-zone interactions

The macroscopic behaviour of a fault zone can be described by a classic Coulomb friction law and static^kinetic rheology. The critical failure stress leading to the activation of a single shear zone segment then depends on the normal stress acting on the future fault plane. It is known that the seismic cycle on a main fault patch can be modulated by surrounding fault activations, leading to interaction with the main segment, or by other external stress perturbations. The results presented here stem from analytical assessments and 2-D numerical elastic models. They show that an earthquake recurrence-time variation with continuing deformation system development is not necessarily connected to fault interaction processes under the above assumptions. Instead, aperiodicity can result from a non-ideal orientation of the rupture plane in the simplest possible homogeneous stress ¢eld, even when constant loading rate and frictional parameters are assumed. This e¡ect can still be found in the multifault geometries we studied, where the interaction of segments determines the seismicity patterns of the system to varying extents. Our results suggest that a stable earthquake periodicity on non-changing fault sets will seldom be found in nature. We propose a reconsideration of the ideas leading to a hypothesized steady seismic cycle in earthquake prediction models.