Regularities in the manifestation of earthquake precursors in the ionosphere and near-surface atmospheric electric fields in Kamchatka

The data of hourly measurements of ionospheric parameters in Petropavlovsk-Kamchatsk are analyzed for the period 1998–2002. In the vertical component of near-surface atmospheric quasistatic electric field Ez, earthquake precursors in the form of anomalous negative bays have been found earlier. In some cases, anomalously high sporadic layer Es, interpreted as an ionospheric precursor of an earthquake, was observed simultaneously with anomalous negative bays in Ez. All these cases were correlated with earthquakes of different magnitudes which occurred with a significant time delay (more than five days) after the precursor appearance. Based on the whole data set (including those for simultaneously measured Es and Ez), empirical dependences linking the prediction time of a precursor, earthquake magnitudes, and the distance from the observation point to the epicenter, are presented. It is shown that these dependences are close to those obtained earlier for long-term earthquake precursors in near-surface geophysical fields of the same seismoactive region. Estimates of the prediction time for earthquake precursors on the boundaries of preparation zones are presented.