Those sounds Sunday night were not sonic booms or the Turrialba volcano blowing its top.
Some government and police agencies reported calls of concern from the citizenry, and the Red Sismológica Nacional said that the sounds were atmospheric and unrelated to the volcano.
Such sounds sometimes are fodder for those alternative science sites that see mystery in everything. The sounds Sunday were
certainly a form of thunder, although no rain was generated.
There were at least two distinct sounds that resembled distant thunder shortly after 8 p.m.
Residents of Alajuela told the Red Sismológica that the sounds were particularly strong there.
Such naturally occurring sounds sometimes have been linked to flying saucers, terrorism or heavenly beings by those who exploit the fears of the public.