Several mechanoelectromagnetic effects are analysed as probable generating mechanisms of electromagnetic impulses produced by an earthquake in its focus. Based on a simple mechanical concept of earthquakes and well-known theories of electrokinetic, piezomagnetic and induction effects, a dipole model of an earthquake-driven electromagnetic source is developed. Corresponding electric and/or magnetic dipole moment values are calculated as functions of earthquake focus parameters and generating mechanisms and are used to estimate the field intensities observable on the surface at different distances from an epicenter of an earthquake of a given magnitude (M). Calculated field values are compared with observational data.