Multifractal detrended fluctuation analysis of co-seismic electromagnetic signals from a magnetotelluric monitoring station in Northern Algeria
摘要
The present study employs multifractal detrended fluctuation analysis to investigate the multifractal properties of the earthquake-related electromagnetic fields. The electromagnetic data were collected at the Médéa Geomagnetic Observatory in Algeria, where continuous magnetotelluric measurements have been conducted since late 2018. The recorded time series were pre-processed to improve the detection of seismo-electromagnetic signals associated with the passage of seismic waves, known as co-seismic electromagnetic signals. By using two techniques, the continuous wavelet transforms and digital filtering, co-seismic electromagnetic signals were identified within a frequency range extending from 1 Hz to higher frequencies. The comparison using multifractal detrended fluctuation analysis between raw and filtered co-seismic electromagnetic time series revealed significant differences in scaling behaviour and fractal properties. High-pass filtering effectively extracted co-seismic features by suppressing low-frequency components, underscoring the critical role of low-frequency dynamics in their multifractal structure. Furthermore, the multifractal analysis results reveal that the co-seismic electromagnetic signals related to four earthquakes (ML ≥ 4) exhibit distinct multifractal properties, characterized by two scaling regimes separated by a crossover. The generalized Hurst exponents decrease monotonically with increasing statistical moments (q) for the co-seismic electromagnetic signal, reflecting a spectrum of intertwined fractal structures. The multifractal spectra of the co-seismic electromagnetic signals are smooth, indicating strong multifractality. The calculated width parameter of the multifractal spectra is higher for the co-seismic electromagnetic signals, confirming their higher degree of multifractality. This multifractal analysis underlines the inherent complexity of earthquake-related electromagnetic signals and underscores the utility of multifractal analysis as a robust tool for characterizing seismo-electromagnetic signals.
Research highlightsMF-DFA reveals multifractal properties of earthquake-related electromagnetic signal. Magnetotelluric measurements used to study the seismo-electromagnetic signal. Using robust techniques to extract the co-seismic electromagnetic signal. Co-seismic electromagnetic signals exhibit strong multifractality.