Long-Memory and Fractal Trends in Variations of Environmental Radon in Soil: Results from Measurements in Lesvos Island in Greece

Abstract

This paper presents evidence of trends of fractal properties and long memory in three-month variations of radon in soil, in Lesvos Island, Greece. The methodology employed consists of sliding-window (a) detrended fluctuation analysis, (b) fractal analysis, (c) rescaled range analysis and (d) fractal dimension analysis with the methods of Higuchi, Katz and Sevcik. During measurements two mild earthquakes occurred in the vicinity. The results of the detrended fluctuation analysis revealed four peaks with slopes between 1.2 and 1.5. The fractal analysis method resulted in three peaks with persistent power-law exponent values in the range 2.2 and 3.0. The rescaled-range analysis indicated persistent Hurst exponents between 0.7-0.9 and in some segments, between 0.9-1. The fractal dimension analysis showed four peaks with fractal dimensions in the range 1.3-2.0 (Higuchi and Katz methods) and 1.0-1.5 (Sevcik method). The results were compared in terms of conversion to Hurst exponents. Several persistent segments were addressed, along with persistency-anti-persistency switching instances. Potential geological sources are discussed and analyzed.