Continuous monitoring of 222Rn and its progeny at a remote station for seismic hazard surveillance

An experimental station to monitor variations in radon and radon progeny concentrations in the gases from the thermal springs at Bakreswar, West Bengal, India has been installed. This is essentially a part of a continuous, automated, multi-parametric geochemical monitoring system (GMS) installed with a view to detect probable earthquake-related precursory changes in the spring gas emanations. The entire data acquisition system is computer driven and fully automated. Instrument readings acquired over a 24-h interval are transmitted through a tele-link facility from the field laboratory located at the thermal spring site situated about 250 km away, once a day, to a workstation at our Centre in Kolkata for analysis and storage. After the system was installed during mid-December, 2004, concurrent anomalous changes in concentration profiles of 222Rn, 218Po and 214Bi occurred beyond 2σσ level four times during the period of present observation duration up to February 04, 2005. The monitored anomalies may be attributed to precursory dilatation responses arising due to earthquakes that had occurred subsequently in Indonesia and the Andaman and Nicobar Islands. The observed variations reveal evidence of pre-seismic radioactive heterogeneities in escaping subsurface fluids from the monitored thermal spring gases.