Seismo-ionospheric effects of the strong crustal earthquakes in the Pacific region

摘要

Hourly relative deviations of the critical frequencies of the ionospheric layers from the running median values according to the observations at Japan stations of the vertical sounding of the ionosphere during periods of preparation of the strong crustal earthquakes with magnitude M >= 6.0 and the hypocenter depth h < 50 km are considered. Seventeen earthquakes for 1994-2000 with the epicentral distances to the vertical sounding stations R = 30-900 km were selected. It was obtained that for a few days prior to the earthquake, the positive deviations both in foF2 and in fEs prevail, leading, in particular, to an increase in the mean nighttime values of the electron density at the F region maximum. A triple relation between anomalous variations in the critical frequencies, magnitude of the preparing earthquake, and epicentral distance was found: the closer epicenter and strongly earthquake the earlier possible ionospheric precursors are observed.