Singular spectral and control chart analysis of soil radon and thoron time series for forecasting seismic activities

Anomalies in soil radon (222Rn) and thoron (220Rn) time series data (TSD) have been reported in many studies prior to earthquakes, suggesting both radioisotopes may serve as earthquake precursors. In the present study, periodic oscillations are being observed in measured time series of soil radon, thoron, and meteorological parameters viz., pressure, temperature, and humidity. Each time series consists of 15,692 measurements taken over a 40-min sampling period. Singular spectrum analyses (SSA) have been used to identify and split the periodic and aperiodic components. Each of the time series has been tested for the normal distribution using KolmogorovSmirnov (K-S) test, the Anderson-Darling (A-D) test, and the Shapiro-Wilk (S-W) test. Results show the nonuniformity of the soil radon and thoron time series. Periodicities in each of the TSD have been studied using periodograms. Control charts have been drawn for radon and thoron time series data (TTSD) to check if any anomalous behavior exists in the time series. Anomalies in TSD have been analyzed for the seismic events that occurred during the study time. The finding of study show that TTSD exhibited unusual behavior prior to the occurrence of the earthquakes.