Geoscience Reference
In-Depth Information
how these signals are generated and what information they may provide has remained
an elusive goal (Bernard et al., 1997; Hough, 2002; Kagan, 1997; Kanamori, 1996;
Knopoff, 1996; Park, 1997; Uyeda, 1998).
Nature of Pre-earthquake Signals
The dilatancy theory (Brace et al., 1966) fits a simple mechanical concept. It is based
on the observation that, when rocks are stressed, they expand normal to the stress vec-
tor and change their pore volume. This can account for bulging of Earth's surface and
for changes in the resistivity due to pore water (Brace, 1975).
Earthquake Lights
Earthquake lights have been observed since ancient times (Derr, 1973; Galli, 1910;
Mack, 1912; Tributsch, 1984). Based on over 1,500 reports, Musya (1931) stated:
“The observations were so abundant and so carefully made that we can no longer feel
much doubt as to the reality of the phenomena” (Terada, 1931). Nonetheless, doubts
persisted in the scientific community even beyond 1960s when EQLs were photo-
graphed during an earthquake swarm at Matsushiro, Japan (Yasui, 1973). Hedervari
and Nosczticzius (1985) covered many observations in Europe. St-Laurent (2000)
evaluated reports of luminous phenomena sighted at the time of the Saguenay earth-
quake in Canada. Tsukuda (1997) reported luminous phenomena associated with the
January 16, 1995 Kobe earthquake. Similar observations were made in Mexico (Araiza-
Quijano and Hernandez-del-Valle, 1996) and other seismically active regions (King,
1983; Lomnitz, 1994).
Low Frequency Electromagnetic Emissions
Low frequency electromagnetic (EM) emissions possibly related to pre-earthquake
activity have attracted attention over the past 10-20 years (Fujinawa and Takahashi,
1990; Gershenzon and Bambakidis, 2001; Gokhberg et al., 1982; Molchanov and
Hayakawa, 1998; Nitsan, 1977; Vershinin et al., 1999; Yoshida et al., 1994; Yoshino
and Tomizawa, 1989). Other authors report local magnetic field anomalies (Fujinawa
and Takahashi, 1990; Gershenzon and Bambakidis, 2001; Kopytenko et al., 1993;
Ma et al., 2003; Yen et al., 2004; Zlotnicki and Cornet, 1986) or increases in radio-
frequency noise (Bianchi and al., 1984; Hayakawa, 1989; Martelli and Smith, 1989).
Mercer and Klemperer (1997) modeled the EM emissions prior to the 1989 M = 7.1
Loma Prieta earthquake (Fraser-Smith et al., 1990) assuming streaming potentials
caused by the movement of water along the fault plane. Sometimes no EM emissions
are recorded, which has caused considerable consternation in the science community
(Karakelian et al., 2002).
Ionospheric Perturbation
The ionosphere marks the transition from the Earth's atmosphere to the vacuum of
space. It is a highly dynamic region where the solar radiation creates a plasma of ions
and free electrons, which partly decays during the night. Prolonged ionospheric pertur-
bations were observed before the great 1960 Chilean earthquake (Warwick et al., 1982)
and the 1964 “Good Friday” earthquake in Alaska (Davis and Baker, 1965). Changes
