Scaling characteristics of ULF geomagnetic fields at the Guam seismoactive area and their dynamics in relation to the earthquake
نویسندگان
چکیده
The long-term evolution of scaling (fractal) characteristics of the ULF geomagnetic fields in the seismoactive region of the Guam Island is studied in relation to the strong (Ms = 8.0) nearby earthquake of 8 August 1993. The selected period covers 10 months before and 10 months after the earthquake. The FFT procedure, Burlaga-Klein approach and Higuchi method, have been applied to calculate the scaling exponents and fractal dimensions of the ULF time series. It is found that the spectrum of ULF emissions exhibits, on average, a power law behaviour S(f ) ∝ f , which is a fingerprint of the typical fractal (self-affine) time series. The spectrum slope β fluctuates quasi-periodically during the course of time in a range of β = 2.5−0.7, which corresponds to the fractional Brownian motion with both persistent and antipersistent behaviour. An tendency is also found for the spectrum slope to decrease gradually when approaching the earthquake date. Such a tendency manifests itself at all local times, showing a gradual evolution of the structure of the ULF noise to a typical flicker noise structure in proximity to the large earthquake event. We suggest considering such a peculiarity as an earthquake precursory signature. One more effect related to the earthquake is revealed: the longest quasiperiod, which is 27 days, disappeared from the variations of the ULF emission spectrum slope during the earthquake, and it reappeared three months after the event. Physical interpretation of the peculiarities revealed has been done on the basis of the SOC (self-organized criticality) concept.
منابع مشابه
Fractal analysis of the ULF geomagnetic data obtained at Izu Peninsula, Japan in relation to the nearby earthquake swarm of June?August 2000
In our recent papers we applied fractal methods to extract the earthquake precursory signatures from scaling characteristics of the ULF geomagnetic data, obtained in a seismic active region of Guam Island during the large earthquake of 8 August 1993. We found specific dynamics of their fractal characteristics (spectral exponents and fractal dimensions) before the earthquake: appearance of the f...
متن کاملMultifractal analysis for the ULF geomagnetic data during the 1993 Guam earthquake
In our previous papers we have shown that the fractal (monofractal) dimension (Do) showed a significant increase before the Guam earthquake occurred on 8 August, 1993. In order to have a further support to this precursory effect to the general rupture (earthquake) we have carried out the corresponding multifractal analysis (by means of detrended fluctuation analysis) for the same data to study ...
متن کاملFractal analysis for the ULF data during the 1993 Guam earthquake to study prefracture criticality
An extremely large earthquake (with magnitude of 8.2) happened on 8 August 1993 near the Guam island, and ultra-low-frequency (ULF) (frequency less than 1 Hz) electromagnetic fields were measured by 3-axis induction magnetometers at an observing station (with the epicentral distance of 65 km) with sampling frequency of 1 Hz. In order to study electromagnetic signature of prefracture criticality...
متن کاملIdentification of Sources of Geomagnetic Variations Using Detrended Fluctuation Analysis (DFA)
This report is an attempt to use Detrended Fluctuation Analysis (DFA) to relate scaling properties of ground-based ULF magnetic field data to occurrence of earthquakes. The magnetic field data are from the South European Geo-magnetic Array (SEGMA) (Vellante et al., 2002). Several moderate earthquakes (4.3 < M < 5.5) occurred in the Adriatic region during November-December 2004. Thus a seven mon...
متن کاملAn attempt to find precursors in the ULF geomagnetic data by means of flicker noise spectroscopy
The flicker noise spectroscopy which is a new phenomenological method for the retrieval of information contained in chaotic time signals, is based on the analysis of recognizable irregularities (pulse, jumps, and discontinuities of derivatives of various order). This method is applied to the ULF (ultra-low-frequency) data observed at Guam in 1992– 1994, in order to study the temporal nonlinear ...
متن کامل