Assessment of Rn-222 continuous time series for the identification of anomalous changes during moderate earthquakes...

Over years, soil radon (Rn-222) measurement was started at Multi-parametric Geophysical Observatory (MPGO), Ghuttu, Garhwal Himalaya to assess the earthquake precursory signatures. We carried out a statistical analysis to examine anomalous soil radon emanation during the occurrence of local earthquakes. Twenty earthquakes of moderate and bigger magnitude are occurred within 300 km from MPGO, Ghuttu during 2009-2017. Continuous time series highlight a high effect of rainfall precipitation on the soil radon emanation measured at 10 m depth. During monsoon period (June to September), high rain precipitation at the recording site cause a high variation in the radon emanation. In spite of our best efforts, it is difficult to isolate the complex behavior of heavy and abrupt occurrence of rain from the soil radon data. Preferably, the data of 11 events of the pre- and post-monsoon are evaluated to identify the seismic origin effect on soil radon. To examine these anomalous variations, statistical analysis of soil radon data is carried out by calculating mean (m), and then obtaining standard deviation (σ) from mean values. Changes in the soil radon concentration are treated anomalous for values exceeding one and two standard deviations (m±σ and m±2σ) from the mean value for the selected duration. Two nearby and the strongest events suggests pre-seismic variations which are related to the earthquake precursory signatures. The observed results are explained in the light of dilatancy- diffusion model.