부산대학교 도서관

Activity of 222Rn gas in soil has been recorded continuously at three monitoring centres, namely Ravangla and Diphu in the Eastern Himalayan region and Tantloi in the geothermal region of eastern India in order to determine possible precursors induced by seismic activity within a few hundred kilometres of the monitoring stations. The recorded data show that various physical and meteorological parameters affect the outflow of radon gas from soil, leading to very complex nonlinear non-stationary soil 222Rn time series. Therefore, a two-step nonlinear technique consisting of empirical mode decomposition and Hilbert–Huang transform has been used for analysis of the simultaneously recorded soil radon data. A number of precursory anomalies caused due to earthquakes of magnitude around 5.0 within 500 km epicentral distance from each monitoring station have been found in the recorded time series of radon in soil at all three centres. An anomaly has been observed simultaneously from the three monitoring stations preceding an earthquake in the common region monitored by the centres. This demonstrates that monitoring of soil radon precursor by a network of stations can be a promising method for understanding earthquake generating processes.