Seismic induced soil gas radon anomalies observed at multiparametric geophysical observatory, Tezpur (Eastern Himalaya), India: an appraisal of probable model for earthquake forecasting based on peak of radon anomalies

We applied multiple linear regressions to scrutinize the maximum variability produced in soil gas radon (Rn-222) by pressure, temperature and rainfall. Statistical methodologies were applied to discriminate the effect of pressure, temperature and rainfall for precise identification of seismic induced anomalies. High Rn-222 anomalies (HRA) as well as Low Rn-222 anomalies (LRA) were apparent. There were nine earthquakes ( M w ≥ 3) which were discernible to be manifested by preseismic soil gas Rn-222 anomalies. Correspondingly, observation centered on radon data set considering the precursory time ‘ T ’ (days), epicentral distance ‘ D ’ (km) and magnitude ‘ M ’ ( M w ) has been derived as Log (DT) = 0.79 M + b . The discernible linear equation was found to be substantial with value of coefficient ‘ b ’ as 0.18 and approximately equal to those obtained by various investigators. In general coefficient ‘b’ is assigned as 0.15 for gaseous geo-seismic precursor. The value of coefficient ‘ a ~ 3.51’, ‘ b ~ 0.18’ and correction factor ‘ K ~ 0.49 (kBqm-3 d) −1/2 were estimated empirically for the first time in Tezpur (Eastern Himalaya), India region. The calculated empirical value of ‘ a ’ by us gives another form of precursory manifestation zone ( D ) equation as D ~ 10 0.58 M . The values of coefficient ‘ a ’, ‘ b ’ and correction factor ‘ K ’ estimated for Tezpur, Assam (Eastern Himalaya) region perhaps can be used for probable earthquake forecast in the region constrained by the peak of the radon anomaly. The number of earthquakes registered was meager and further long-term analysis can estimate more precise and robust values of these parameters for soil gas Rn-222. The investigation also reassures us in a physical sense that seismic induced soil gas Rn-222 perturbation do exist in nature. The investigation is a probable approach for identification of seismic induced anomalies in soil gas Rn-222 and their characteristics for possible earthquake forecasting.