Linking electromagnetic precursors with earthquake dynamics: An approach based on nonextensive fragment and self-affine asperity models

摘要

EM emissions in a wide frequency spectrum ranging from kHz to MHz areproduced by opening cracks, which can be considered as precursors of generalfracture. An important feature, observed on both laboratory and geophysicalscale, is that the MHz radiation systematically precedes the kHz one. Yet, thelink between an individual EM precursor and a distinctive stage of the EQpreparation comprises a crucial open question. A recently proposed two-stagemodel on preseismic EM activity suggests that the MHz EM emission is due to thefracture of the highly heterogeneous system that surrounds the fault. Thefinally emerged kHz EM emission is rooted in the final stage of EQ generation,namely, the fracture of entities sustaining the system. In this work we try tofurther penetrate and elucidate the link of the precursory kHz EM activity withthe last stage of EQ generation building on two theoretical models for EQdynamics. Firstly, the self-affine model states that an EQ is due to theslipping of two rough and rigid fractional Brownian profiles, one over theother, when there is an intersection between them. Secondly, thefragment-asperity model, rooted in a nonextensive Tsallis framework startingfrom first principles, consists of two rough profiles interacting via fragmentsfilling the gap. In the latter approach, the mechanism of triggering EQ isestablished through the interaction of the irregularities of the fault planesand the fragments between them. This paper shows that these models of EQdynamics can be linked with the detected kHz EM emission. In this framework ofanalysis of preseismic EM activity, we identify sufficient criteria that offerthe possibility to discriminate whether a seismic shock is sourced in thefracture of fragments filling the gap between the rough profiles or in thefracture of "teeth" distributed across the fractional Brownian profiles thatsustain the system.