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Fractal analysis of ULF geomagnetic data associated with the Guam Earthquake on August 8, 1993
Author(s) -
Hayakawa Masashi,
Ito Tetsuya,
Smirnova Natalia
Publication year - 1999
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1999gl005367
Subject(s) - noon , seismology , quake (natural phenomenon) , geology , earth's magnetic field , fractal , earthquake prediction , foreshock , observatory , geophysics , physics , atmospheric sciences , magnetic field , astronomy , mathematical analysis , mathematics , quantum mechanics , aftershock
This paper presents a fractal analysis of the ULF electromagnetic data obtained at Guam observatory during a strong (Ms=8.0) earthquake occurred on August 8, 1993 near the Guam island. We have already reported the presence of seismogenic ULF emissions for this quake (Hayakawa et al., GRL, 1996). The chosen period covered four months before and two months after the earthquake. It was found that the spectrum of emissions at noon exhibited a power law behavior f −β which is typical for self‐organized critical dynamics. The slope of the spectrum in the noon sector fluctuates in a range from 2.5 to 0.7 with a tendency to gradually decrease during the process of the earthquake preparation. We consider this to be a candidate for a precursory signature. The similar effect was found for the night sector. We suggest that the focal zone was at the critical stage of self‐organized criticality process before the quake, related to active microfracturing processes followed by the generation of ULF emissions as we detected.