Ionospheric effects of ground motion: The roles of magnetic field and nonlinearity

Transformation of infrasound to magnetic sound upon propagation from ground level up to the ionosphere is considered. It is shown that upon entering the ionospheric layers at altitudes of order 150-170 km, the wave dynamics changes sharply. Nonlinear effects, including shock formation, are also considered. The shocks are typically formed in a relatively narrow range of altitudes, or not formed at all. Generalization of the model to a case of oblique propagation is briefly considered, and the effects of atmospheric profile variation and of finite plasma conductivity are estimated. Along with providing qualitative insight, the model gives some realistic estimates for waves generated by earthquakes.