A survey of mathematical models for electromagnetic earthquake precursors in the ionosphere: numerical results

Perturbations in the electric properties of the ionosphere are observed in correspondence of solar activity (solar wind-magnetosphere-ionosphere coupling) and tectonic activity (litosphere-atmosphere-ionosphere coupling). In this work, we focus on the connection between seismic activity and ionospheric perturbation relevant for definition of electromagnetic seismic precursors observed using electric and/or magnetic measurements collected by ground-based and spaceborne sensors.

We provide a survey of some mathematical models of earthquake precursors in the ionosphere. A quantitative approach is based on the modelling of oscillations of pressure and/or density in the troposphere, acoustic gravity waves induced by earthquake activity. Another approach is based on the electromagnetic modelling of the atmosphere to explain the observed anomalies of the electric and magnetic fields, as well as of the electron content. We discuss a few approximation of the Maxwell’s equations as the on in the range of low frequencies, e.g. the VLF signals used in many studies on seismic precursors. We also discuss the inverse problem of estimating the spatial distribution of subsurface electric charges, induced by the tectonic movement and rock friction in the earthquake preparatory phase, which can explain the measured electric and/or magnetic anomalies observed before earthquakes. Numerical methods are described and results presented.