The original purpose of this investigation started in 1996 was to study the radiological impact on the local population of
the village of Chichiviriche de La Costa. But, soon after the major earthquake (Ms=6.8) in the state of Sucre on July 9, 1997,
the objective was changed to study the fluctuation of radon (222Rn) to see if it could be correlated to seismic activity and/or if the amonlous change just before the earthquake can be considered
a precusor for it. Measurements of222Rn by simply de-gassing about 250 ml of natural thermal water employing a Pylon AB-5 radiation monitor and counting the radiation
after it reached equilibrium were performed. The values for four sampling periods in the first half of 1996 were about 17
Bq/l of222Rn, a month before the earthquake they were less than 15 Bq/l and increased about 70% to 25 Bq/l two days before the seismic
event. In about two weeks, they returned to about 18 Bq/l. But, surprisingly, they have gradually increased to about 35 Bq/l,
before leveling off at about 27 Bq/l.