Foreshocks and b-value: bridging macroscopic observations to source mechanical considerations

TL;DR

This paper enhances the OFC earthquake model with an analytical expression linking dissipation to material properties and heterogeneities, explaining foreshock b-value variations through material softening, validated by cellular automaton simulations.

Contribution

It introduces an analytical enrichment of the OFC model that connects fault material properties and heterogeneities to seismicity patterns, especially foreshock b-value behavior.

Findings

Analytical expression linking dissipation to elastic and heterogeneity properties.

Modeling of low b-values through material softening.

Simulation validation of model predictions.

Abstract

Spring-block models, such as the Olami-Feder-Christensen (OFC) model, were introduced several years ago to describe earthquake dynamics in the context of selforganized criticality. With the aim to address the dependency of the seismicity style on sources material properties we present an analytical enrichment of a 2D OFC model. We concluded with an analytical expression which introduces, through an appropriate constitutive equation, an effective dissipation parameter a related analytically not only with the elastic properties of the fault plane, but also with stochastic structural heterogeneities and structural processes of the source through a gradient coefficient. Moreover, within the proposed formulation the low b-values experimentally observed in foreshock sequences can be modeled by a process of material softening in the seismogenic volume. To check our analytical findings a cellular automaton was build-up whereas simulation results have verified models predictions for the evolution of b in macroscopic records.