Radon and Helium Fluctuations Prior to Seismic Events in Thermal Spring Gas Hirok Chaudhurr'", Nisith K. Das 2 , Rakesh K. Bhandari", Debasis Ghose', Prasanta Sen 1 and Bikash Sinha 1 ,2 'Saha Institute of Nuclear Physics, 1 /AF Bidhannagar,Kolkata-700064, India. 2Variable Energy Cyclotron Centre, 1/ AF Bidhannagar, Kolkata-700064, India. Abstract Radon 222, radon progeny, qamrna, and helium escaping from the hot springs at Bakreswar (23° 52' 30" N; 87°02' 30" E), West Bengal, are monitored round the clock to observe concentration changes. The data transmitted from the field observatory through satellite using C-Band transponder to our Centre at Kolkata unfold two distinct patterns. A regular small undulation generated by diurnal strain changes due to earth tides is observed. Infrequently however anomalous large, positive as well as negative, swings are recorded that may easily correlate with regional earthquake occurrences. The paper describes details of the experimental set-up at the monitoring station along with a few correlated seismic events and the mathematical modeling of the data set. Keywords: Thermal springs, geochemical monitoring, radon, gamma, helium, earthquake. 1 INTRODUCTION It has long been recognized that crustal movements as well as anomalous changes in terrestrial gas concentrations are premonitory effects to earthquakes [1]. Gas variations are the secondary consequences to the building up of earth stresses that lead to seismicity. There are numerous observations which show that gas anomalies, as a rule, do not follow a bench mark but appear #Corresponding authors: Hirok Chaudhuri; chaudhuri_hirok@yahoo.co.in, Nisith k.Das; nkdas@veccal.ernel.in