An examination of the nature and dynamics of seismogenesis in South California, USA, based on Non-Extensive Statistical Physics

Abstract

We examine the nature of the seismogenetic system in South California, USA, by searching for evidence of complexity and non-extensivity in the earthquake record. We attempt to determine whether earthquakes are generated by a self-excited Poisson process, in which case they are independent, or by a Critical process, in which long-range interactions in non-equilibrium states are expected (correlation). Emphasis is given to background seismicity, i.e. to the rudimentary expression of the seismogenetic system. We use the complete and homogeneous earthquake catalogue published by the South California Earthquake Data Centre, in which aftershocks are either included, or have been removed by a stochastic declustering procedure. We examine multivariate cumulative frequency distributions of earthquake magnitudes, interevent time and interevent distance in the context of Non-Extensive Statistical Physics, which generalizes the additive Boltzmann-Gibbs thermodynamics to non-additive (non-extensive) dynamic systems. Our results indicate that the seismogenetic systems of South California are generally sub-extensive complex and certainly non-Poissonian. Background seismicity exhibits long-range interaction as evidenced by the overall increase of correlation observed by declustering the earthquake catalogues, as well as by the high correlation observed for earthquakes separated by long interevent distances. The results compare very well with those obtained in previous work for the seismogenetic systems of North California. Specifically, the Walker Lane – Eastern California Shear Zone on one hand, and the San Andreas Fault system – south California Continental Borderland region on the other, appear to comprise fault networks with different dynamics and expression. The former exhibits persistent, very high correlation and has attributes of (stationary) Self-Organized Criticality (SOC). The latter exhibits high correlation mainly at long ranges and has attributes of evolutionary of (Self-Organized) Criticality. All in all, our results are compatible with simulations of small-world fault networks in which free boundary conditions at the surface allow for self-organization and criticality to develop.