Geoscience Reference
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60
B , nT/Hz 1/2
50
40
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0 0
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20 30
t , days (UT)
Fig. 10.1 Power spectrum of electromagnetic noise observed in October 1989 at Corralatios
station, Central California. The frequency of measured channel is 7.32 mHz. The arrow shows
the moment of Loma Prieta occurrence. Adapted from Fraser-Smith et al. ( 1990 )
(Dea et al. 1991 ; Dea and Boerner 1999). An increased ULF magnetic activity has
been observed before the great EQ in Indonesia, Biak, M D 8:1 at the distance
about 80 km (Hayakawa et al. 2000 ). On the other hand Fraser-Smith et al. ( 1994 )
have not observed electromagnetic noise exceeding background or any unusual
phenomena associated with either the 1992, M D 7:4 Landers EQ or the same
Northridge earthquake. Based on this fact and taking into account that the receivers
were located far away from the EQ epicenter, one can suppose that the zone of ULF
precursor reception does not exceed about 100 km (Fraser-Smith et al. 1994 ). We
will return to this point later after theoretical analysis.
However, some skepticism always persists as to the plausibility of ULF noise
variations in possible association to impending EQs (Park et al. 1993 ; Geller
1996 , 1997 ; Bakun et al. 2005 ; Campbell 2009 ; Thomas et al. 2009 ). Though this
controversy is concentrated both on the measurement reliability and also on the
mechanisms which are able to explain the observed effects.
In spite of this skepticism the majority of researchers believed that the ULF
electromagnetic noise can be considered as a promising candidate for short-term
EQ prediction. The networks of sensitive three-component ULF magnetometers and
electric sensors have been installed in Kamchatka peninsula, Russia (Uyeda et al.
2002 a; Gladychev et al. 2002 ), Japan (Hobara et al. 2002 ; Hattori 2004 ; Hayakawa
et al. 2011 ), Taiwan (Hattori et al. 2002a ), Greece (Makris et al. 2003 ), and India
(Arora et al. 2012 ).
The recent studies of the ULF perturbations have shown that the signal-to-noise
ratio is small (Fraser-Smith et al. 1990 , 1994 ; Kopytenko et al. 1990 , 1993 ; Johnston
et al. 1994 ; Yepez et al. 1995 ; Hayakawa et al. 1996 , 2000 , 2007a , 2011 ; Akinaga
et al. 2001 ; Ismaguilov et al. 2001 ; Gotoh et al. 2002 ; Hattori et al. 2002b , 2004 ;
Hattori 2004 , 2013 ;Ohtaetal. 2005 ; Hobara et al. 2012 ) so that the problem is how
 
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