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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS009 Oral Presentation 2037
Analysis on The Dynamical Nature of Seismo-Electromagnetic Signal
Dr. Dong Jiping
Research & Development Center China Academy of Space Technology IASPEI
Electromagnetic phenomena have been recognized as a promising candidate for the short-term
earthquake prediction (Hayakawa, 2005). There are a lot of reports concerning about electromagnetic
signal observed in a wide frequency range from ULF to HF before earthquakes occur. Electromagnetic
radiation during experiments of rock fracture also convinces us that seismo electromagnetic signal
comes directly from seismic source, considering that earthquakes occur when rock body fractures
suddenly due to high stress in crust. It seems that seismic electromagnetic signal is closely related to
fracturing process of rocks in crust. So as to this, Several radiation mechanisms of seismic electric
magnetic signal, such as stress variation effect in seismogenic zone, piezoelectricity or piezomagnetic
effect, and electromagnetic emission associated with microscopic cracking in rocks, have been brought
forward. Comparing to field observation, none of these mechanisms can explain all abnormal behavior
of seismic electric magnetic signal, but electron emission effect with microscopic cracking in rocks is
relatively some reasonable and with catholicity. For example, no observable stress variation corresponds
to characteristic time of minutes or hours for abnormal Electromagnetic observation, and piezoelectricity
or piezomagnetic effect need large number of orderly arrange dcrystalloids in crust. There are three
main viewpoints about the mechanism of electron emission effect with rock cracking. The first viewpoint
is surface charging mechanism, suggesting that the surface charge on crack walls in rock is caused by
appearances of excited hole and electron trapping centers (point defects) on a newly created surface of
rocks when fault asperities are sheared. The second is based on that seismic electromagnetic signal is
caused by emission of electrons in crack tip end and the model of compressed atoms. Even a electric
quadrupole model is proposed by Guo Ziqiang etc to simulate the extending process of microscopic
cracking in rocks and frequency spectral bandwidth gotten as 0.5 1.0MHz. The emission of electrons in
crack tip end and the model of compressed atoms are supported by the third opinion, and otherwise, a
capacitor model is proposed as a supplement suggesting that charging and discharging in crack tip
happens in the extending process of microscopic cracking and the lower or higher frequencies are
explained well.After all, the radiation mechanism of seismo electromagnetic signal is still not known
well. It seems much difficult for us to check which model is more reasonable by observation in field
around ground. There is still much uncertainty in actual observational, such as amplitude, time series
and direction and so on. The uncertainty seems relative to the dynamic radiation process.Another
convincing evidence of seismic electromagnetic radiation caused by fracturing process of rocks is that
there found abundant cracks in rocks. Once the stress in crust reaches a certain value, the seismological
system would get into a nonlinear phase and the numberless cracks in focal dimension scope would
fracture thus macroscopical seismic electromagnetic signal would be generated and
observed.Considering that seismological Gutenberg-Richter Equation accords with power law, a typical
fractal phenomena, much similar to the behavior of fragmentation in mining and eruption, as well as
tectonic distributing. Some authors regard power law as a characteristic of self- similar seismological
system and others suggest that it is a reflection of self-organized critical phenomenon. Although
Gutenberg-Richter Equation is statistically got for global events and for a period of time, it is still often
used for a certain region and for a longer time. In the paper, the power law is used to tiny cracks in
crust rocks with different fractal dimensions for different scales. By the introduction of furcated fractal
dimension, the radiation mechanism caused by fracturing process of rocks is analyzed related to the