Singular spectrum analysis on soil radon time series ( 222 Rn) in Kachchh, Gujarat, India: detection of periodic oscilla
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ORIGINAL PAPER
Singular spectrum analysis on soil radon time series (222Rn) in Kachchh, Gujarat, India: detection of periodic oscillations and earthquake precursors Sushanta Kumar Sahoo 1 & Madhusudhanarao Katlamudi 1
&
Udaya Lakshmi Gakka 2
Received: 9 September 2019 / Accepted: 2 September 2020 / Published online: 17 September 2020 # Saudi Society for Geosciences 2020
Abstract The influence of various meteorological parameters on the observed time series of soil radon (222Rn) in the form of periodic oscillations is profound and well established. An attempt is made in the present study to identify and remove the periodic oscillations using singular spectrum analysis (SSA) to identify earthquake precursors in the time series of soil radon (222Rn) recorded at Badargadh, Kachchh region of Gujarat, India, for the period from February 21 to June 10, 2011. The temperature has shown diurnal oscillations, whereas radon and pressure show the mixture of diurnal and semi-diurnal oscillations. A Butterworth digital filter has been applied to the observed data of all parameters (222Rn, pressure, temperature, and humidity) to remove the long periodic trends (more than 30 days). The periodic and aperiodic components in the time series of soil radon are identified and separated using SSA. While correlating the radon with other parameters, we found that the aperiodic radon has negative correlation with temperature and the radon has positive correlation with humidity and pressure. Two earthquakes of magnitudes M3.7 and M4.2 which occurred on March 26, 2011, and May 17, 2011, respectively, are being investigated to identify anomalies before these earthquakes. These earthquakes are located within a distance of 100 km from Badargadh. Based on the statistical analysis of mean+2*sigma, we observed the anomalous radon signal before the occurrence of these earthquakes with relative percentage of 94–96% at Badargadh. Keywords Radon (Bq/m3) . Temperature (°C) . Pressure (mB) . Humidity (%) . Earthquake precursor
Introduction Identifying the precursors to the earthquake is one of the greatest challenges for geoscience scientists in the twentyfirst century. Among all the precursors, the geochemical precursors are considered as one of the potential candidates. Geochemical parameters, including radon (222Rn), He, CH4, CO2, and N2, are monitored near active faults to identify earthquake precursors (Chaudhuri et al. 2013). Due to its radioactive nature and its origin in the subsurface, 222 Rn reacted significantly in the soil and in Responsible Editor: Amjad Kallel * Madhusudhanarao Katlamudi [email protected] 1
Institute of Seismological Research, Gandhinagar, Gujarat 382009, India
2
Osmania University, Hyderabad, Telangana, India
groundwater to stress/strain changes during the earthquake preparation phase before occurrence of earthquakes (Scholz et al. 1973; Wakita et al. 1991; Virk et al. 2001; Walia et al. 2009; Ghosh et al. 2009). Radon is a decay product of radium with 39 isotopes. Among these isotopes, 222Rn is the most stable i
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