  In this work, it is demonstrated that the Earth's preseismic electric field,
which is registered by a pair of electrodes in contact to the ground surface at
certain distance from the epicentral area, corresponds to the gradient of the
total field generated in the focal area as a function of time and distance from
it. The original form of the generated preseismic field follows closely the
theoretical piezoelectric potential form. The later is obtained after
integration in time of the original registered potential grad data values.
Consequently, the time of occurrence of the imminent earthquake (collapsing of
the rock formation) is estimated by the classical laws of rock fracturing based
on theoretical Rock Mechanics. The methodology has been tested on the grad
potential data, registered in Greece, before four large EQs which took place in
the regional area as follows: Izmit, Turkey EQ (M = 7.8R, 17th August, 1999),
Milos, Greece EQ (M = 5.6R, 21st May, 2002), Kythira Greece EQ (M = 6.9R, 8th
January, 2006) and Methoni, Greece EQ (M = 6.7R, 14th February, 2008). The
obtained results prove the validity of the postulated methodology.
