Scale-free Effects Research Articles

Critical dynamics of fractal fault systems and its role in the generation of pre-seismic electromagnetic emissions

Regional seismicity is known to demonstrate scale-invariant properties in different ways. Some typical examples are fractal spatial distributions of hypocenters, Gutenberg–Richter magnitude statistics, fractal clustering of earthquake onset times, power-law decay of aftershock sequences, as well as scale-invariant geometry of fault systems. In some regions, the observed scale-free effects are likely to be connected to a cooperative behavior of interacting tectonic plates and can be described in terms of the self-organized criticality (SOC) concept. In this work, we investigate a new SOC model incorporating short-term fractal dynamics of seismic instabilities and slowly evolving matrix of cracks (faults) reflecting long-term history of preceding events. The model is based on a non-Abelian directed sandpile algorithm proposed recently by Hughes and Paczuski [Phys. Rev. Lett. 88 (5), 054302-1], and displays a self-organizing fractal network of occupied grid sites similar to the structure of stress fields in seismic active regions. Depending on the geometry of local stress distribution, some places on the model grid have higher probability of major events compared to the others. This dependence makes it possible to consider a time-dependent structure of the background earth crust geometry as a sensitive seismic risk indicator. We also propose a simple framework for modeling ultra-low frequency (ULF) electromagnetic emissions associated with abrupt changes in the large-scale geometry of the stress distribution before characteristic seismic events.