  We investigate the physical mechanism of the GZ-effect that could explain the
production of multiple primaries from an event initiated outside the Earth's
atmosphere. In this case, there would correspondingly be multiple extensive air
showers in temporal coincidence at ground, even for detectors separated by many
kilometers, and also showers initiated by primaries of different energies could
consequently have a common source. We analyse the perspectives and limits of
some models and discuss the experimental counterparts.
