  Starting from the observation that quite often the Earth's oscillating
electric field varies in amplitude, a mechanism is postulated that accounts for
these observations. That mechanism is the piezoelectric one driven by the M1
and K1 tidal components. It is demonstrated how the system: piezoelectricity
triggered in the lithosphere - M1 and K1 tidal components is activated and
produces the amplitude modulated Earth's oscillating electric field. This
procedure is linked to the strain load conditions met in the seismogenic area
before the occurrence of a large EQ. Peaks of the oscillating Earth's electric
field are tightly connected to the M1 peak tidal component and to the timing of
the occurrence of large EQs. Typical examples from real recordings of the
Earth's oscillating electric field, recorded by the ATH (Greece) monitoring
site, are given in order to verify the postulated detailed piezoelectric
mechanism.
