Current Development in Theory and Applications of Wavelets
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Abstract: Ultra-low-frequency (ULF, frequency less than 1Hz)
emissions are considered to be a promising candidate for short-term earthquake (EQ)
prediction. The prefracture criticality of the lithosphere is studied by
applying fractal analysis to the ULF data with the target of an extremely large
EQ (with magnitude of 8.2) happened on August 8, 1993 near the Guam island. In
order to study electromagnetic signature of prefracture criticality, we have
first undertaken the mono-fractal analysis by means of the Higuchi’s method
for the ULF data. Then, it is found that the fractal dimension exhibits five
maxima 99, 75, 52, 21, and 9-4 days before the EQ 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 EQ. 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. Then
in order to have a further support to this precursory effect to the general
rupture (EQ) we have carried out the corresponding multi-fractal analysis (by
means of detrended fluctuation analysis) for the same data to study the
statistical self-similar properties in a wide range of scales. As the result, we
have found that we could observe significant changes in the multi-fractal
parameters such that showed a meaningful decrease about
25 days before the EQ and correspondingly increased because exhibited no significant change at
all. The most sensitive parameter seems to be the non-uniformity factor D.
Correspondingly, the generalized multi-fractal dimension Dqshowed a significant decrease
(whereas Dqshowed no change) and (as already mentioned before) is
reconfirmed to increase before the EQ. These multi-fractal characteristics seem
to be a further support that these changes are closely associated with the EQ as
a precursor to the Guam EQ, providing us with appreciable information on the
pre-rupture evolution of the EQ.
