DFA analysis of SEGMA magnetic field data around the M6.3 Aquila EQ

Recently a preliminary analysis of the magnetic field observations performed at L’Aquila preceding the April 6, 2009 earthquake has been performed (Villante et al, 2010). A possible occurrence of features as i) an increase in the noise background and/or polarization parameter (i.e. the ratio between the amplitude/power of the vertical component and that one of the horizontal component), ii) changing characteristics of the slope of the power spectrum and fractal dimension, and iii) occurrence of short duration pulses have been looked for two years back. It was concluded that the expected ULF disturbances related to earthquakes (if any) are generally weak and sophisticated signal processing methods and a lot of experience are required to evaluate the source of ULF emissions observed at ground. In this report we apply detrended fluctuation analysis (DFA) analysis on fluxgate and search-coil data in ULF range (periods 10-90 sec) for months January-April 2009 available from SEGMA array (Italy, Hungary, Austria and Bulgaria). Remind DFA is a data processing method that allows for the detection of scaling behaviors in observational time series even in the presence of non-stationarities. H and Z magnetic field components at night hours (00-03 UT, 01-04 LT) and their variations at stations AQU, CST, NCK and PAG have been examined and their scaling properties are analyzed depending on geomagnetic and local conditions. As it is expected, the DFA scaling exponents increase when Kp index increases, indicating a good correlation with geomagnetic activity. DFA scaling exponent reveals also local changes –such as a considerable decrease for the H component at AQU station observed in the midst of February. A malfunction of the fluxgate magnetometer at Aquila has been checked up and excluded. Attempts to explain thoroughly this unique feature with artificial and/or natural sources including the enhanced earthquake activity occurred in months January-April 2009 at Aquila district are made.