Detection of earthquake induced radon precursors by Hilbert Huang Transform

• Sub- surface soil gas radon- 222 has been monitored.
• Radon- 222 time series is analyzed for Earthquake Precursor Study.
• The time series is analyzed by means of Hilbert Huang Transformation (HHT).
• Ensemble Empirical Mode Decomposition method is used to detect
• Remove diurnal and semi- diurnal components from the original data set.

Continuous measurement of radon-222 concentration in soil was carried out across duration of one year at a geologically faulted area having high regional heat flow to detect anomalies caused by seismic activities. The data reveals a range of periodicities present in the radon time series. To identify seismic induced radon changes we treat the time series data through various filtering methods to remove inherent periodicities. The Ensemble Empirical Mode Decomposition (EEMD) is deployed to decompose the signal into its characteristic modes. Hilbert Huang Transform (HHT) is applied for the first time on the physically significant modes obtained by EEMD to represent time–energy–frequency of the recorded soil radon time series. After removing the periodic and quasi-periodic constituents from the original time series, the simulated result shows a forceful correlation in recorded radon-222 anomalies with regional and local seismic events.