Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 13 4 2006 10.5194/npg-13-409-2006 http://www.nonlin-processes-geophys.net/13/409/2006/ http://www.nonlin-processes-geophys.net/13/409/2006/npg-13-409-2006.html http://www.nonlin-processes-geophys.net/13/409/2006/npg-13-409-2006.pdf 409 412 2006-08-11 Fractal analysis for the ULF data during the 1993 Guam earthquake to study prefracture criticality Y. Ida M. Hayakawa hayakawa@whistler.ee.uec.ac.jp Department of Electronic Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan 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, we have undertaken the fractal (mono-fractal) analysis by means of the Higuchi's method for the ULF data during the 1993 Guam earthquake. Then, it is found that the fractal dimension exhibits five maxima 99, 75, 52, 21, and 9–4 days before the earthquake main shock, which suggests the ULF electromagnetic signature of nonlinear evolution (in the sense of self-organized criticality) taking place in the lithosphere just before the 1993 large Guam earthquake. That is, there take place step-like changes in the lithosphere during the long-term of the order of several months before the main shock. Burlaga, L. F. and Klein, L. W.: Fractal structure of the interplanetary magnetic field, J. Geophys. Res., 91, 347–350, 1986. Gotoh, K., Hayakawa, M., and Smirnova, N.: Fractal analysis of the gromagnetic data obtained at Izu peninsula, Japan in relation to the nearby earthquake swarm of June–August 2000, Nat. Hazards Earth Syst. Sci., 3, 229–236, 2003. Gotoh, K., Smirnova, N., and Hayakawa, M.: Fractal analysis of seismogenic ULF emissions, Special Issue on "Seismo Electromagnetics and Related Phenmena", edited by: Hayakawa, M., Molchanov, O. A., Biagi, B. F., and Vallianatos, V., Phys. Chem. Earth, Parts A/B/C, 29, 4–9, 419–424, 2004. Hayakawa, M. and Fujinawa, Y. (Eds.): Electromagnetic Phenomena Related to Earthquake Prediction, Terra Sci. Pub. Co., Tokyo, 667p, 1994. Hayakawa, M., Kawate, R., Molchanov, O. A., and Yumoto, K.: Results of ultra-low-frequency magnetic field measurements during the Guam earthquake of 8 August 1993, Geophys. Res. Lett., 23, 241–244, 1996. Hayakawa, M., Itoh, T., and Smirnova, N.: Fractal analysis of ULF geomagnetic data associated with the Guam earthquake on 8 August 1993, Geophys. Res. Lett., 26, 2797–2800, 1999. Hayakawa, M. (Ed.): Atmospheric and Ionospheric Electromagnetic Phenomena Associated with Earthquakes, Terra Sci. Pub. Co., Tokyo, 996p, 1999. Hayakawa, M. and Molchanov, O. A. (Eds.): Seismo Electromagnetics: Lithosphere-Atmosphere-Ionosphere coupling, TERRAPUB, Tokyo, 477p, 2002. Hayakawa, M., Molchanov, O. A., and NASDA/UEC team: Summary report of NASDA's earthquake remote sensing frontier project, in: Special Issue on Seismo Electromagnetics and Related Phenomena, edited by: Hayakawa, M., Molchanov, O. A., Biagi, P. F., and Vallianatos, F., Phys. Chem. Earth, 29, 4–9, 617–626, 2004. Hayakawa, M. and Hattori, K.: Ultra-low-frequency electromagnetic emissions associated with earthquakes, IEEJ Trans. Fundamentals and Materials, 124, 12, 1101–1108, 2004. Higuchi, T.: Approach to an irregular time on the basis of fractal theory, Physica D, 31, 277–283, 1988. Molchanov O. A. and Hayakawa, M.: Generation of ULF seismogenic electromangetic emissions by microfracturing, Geophys. Res. Lett., 22, 3091–3094, 1995. Molchanov, O. A. and Hayakawa, M.: On the generation mechanism of ULF seismogenic electromagnetic emissions, Phys. Earth Planet. Inter., 105, 201–210, 1998. Smirnova, N., Hayakawa, M., Gotoh, K., and Volobuev, D.: Scaling characteristics of ULF geomagnetic field at the Guam seismoactive area and their dynamics in relation to the earthquake, Nat. Hazards Earth Syst. Sci., 1, 119–126, 2001.