the ionospheric Huancayo station located near the magnetic equator during periods of quiet geomagnetic con-
ditions are analyzed for 1957–1987. Ionospheric data for five days prior, one day after, and directly for the days
of 33 strong (with a magnitude M
5.5) earthquakes with epicenters in the American longitudinal sector were used. It is revealed that, in 24 cases 1–5 days prior to the considered earthquakes, a decrease in the critical fre-
quencies by more than 20% with a duration from one to six hours was observed mainly in the nighttime. One
can assume that these effects (at least, part of them) are related to the processes of earthquake preparation. Dis-
turbances were mainly detected in cases when the radius of the earthquake preparation zone exceeded the dis-
tance between the epicenter and the observation station. The need for a further study of the characteristics of
different kinds of coupling “from below” on electrodynamical processes in the low-latitude ionosphere for suc-
cessful recognition of disturbances of the seismogenic nature is noted.