| Study of Seismic Precursory Nature of Soil Radon Recorded Simultaneously at Two Monitoring Stations in Eastern Himalayas Saheli Chowdhury1; Argha Deb1; Chiranjib Barman2; Md. Nurujjaman3; Dipok K. Bora4; 1DEPARTMENT OF PHYSICS, JADAVPUR UNIVERSITY, Kolkata, India; 2DEPARTMENT OF PHYSICS, SIDHO-KANHO-BIRSHA UNIVERSITY, Purulia, India; 3NATIONAL INSTITUTE OF TECHNOLOGY SIKKIM, Ravangla, India; 4DEPARTMENT OF PHYSICS, DIPHU GOVERNMENT COLLEGE, Diphu, India; PAPER: 545/Physics/Regular (Oral) SCHEDULED: 16:45/Wed. 30 Nov. 2022/Andaman 2 ABSTRACT: Anomalous fluctuation of radon concentration in soil is a well-known short-term precursor of earthquakes. Activity of radon (222Rn) gas in soil was monitored continuously for about eight months from late June 2018 to late February 2019, simultaneously at two monitoring stations in the Eastern Himalayas, namely, Ravangla in Sikkim and Diphu in Assam, in search of possible precursors induced by seismic activity within a few hundred kilometres of the stations. Radon activity in soil gas, together with local meteorological parameters such as daily temperature, atmospheric pressure, and precipitation, was recorded with Barasol BMC2 radon monitor which was integrated with sensors for the weather parameters. The data recorded at both sites show that various physical and meteorological parameters affect the outflow of radon gas from soil, leading to a complex non-linear non-stationary soil 222Rn time series. Therefore, a two-step non-linear technique consisting of empirical mode decomposition and Hilbert-Huang transform has been used for analysis of the data (Chowdhury et al. 2017). However, as this method alone is inadequate to identify the effects of regional geophysical factors as well as that of rainfall, the networking approach has been adopted with it. The study looked for precursors for regional earthquakes of magnitude 5.0 or above within an epicentral distance of 500 km from each monitoring station; however, for earthquakes of smaller and larger magnitudes, smaller and larger epicentral zones respectively were considered. A number of earthquake-induced anomalies have been found in the soil radon time series of both stations. In this regard, anomalies were observed almost simultaneously from both centres preceding a M5.3 earthquake that occurred on September 12, 2018 in Kokrajhar, Assam. Moreover, the epicentre of this earthquake was found to be located in the common region monitored by the centres. Hence, monitoring of soil radon concentration utilising a network of stations in earthquake-prone regions may be a promising method for short-term precursors of earthquakes. References: Chowdhury S, Deb A, Nurujjaman M, Barman C, 2017. Natural Hazards 87: 1587-1606. |
