Electric and magnetic field variations arising from the seismic dynamo effect for aftershocks of the M7.1 earthquake of 26 May 2003 off Miyagi Prefecture, NE Japan

Abstract

Some examples of electric and magnetic field variations have recently been reported by Honkura and his colleagues in association with earthquakes, and these variations have been interpreted by them in terms of the seismic dynamo effect. In order to confirm that this effect is a universal phenomenon rather than a phenomenon appearing in a special local condition, we made magnetotelluric (MT) observations above the hypocentral area of the M7.1 earthquake which occurred off Miyagi Prefecture, northeastern Japan, on May 26, 2003. The MT site was selected at a location close to a seismic station belonging to the nation-wide seismic observation network called 'Hi-net', so that we can compare the MT signals with the seismic wave records. During the MT observation period after the mainshock, some moderate-size aftershocks of magnitudes between 2.8 and 4.1 occurred and MT signals appeared in association with all these aftershocks. In order to confirm that MT signals are not due to vibrations of MT equipment, we set up two sets of MT equipment at the same location; in the case of electric field measurements, we used independent electrodes and arranged cables connecting electrodes on the ground for one set and in the air for the other set, and in the case of magnetic field measurements, we buried the induction coils under the ground for one set and hang them in the air for the other set. As for the electric field, the two sets showed exactly the same records. On the other hand, the magnetic field was different from one set to another, but we conclude that the induction coils buried in the ground are more likely to represent the magnetic field due to electric currents flowing in the ground as a result of the seismic dynamo effect.

Ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes

“…Ujihara et al, 2004;Iyemori et al, 2005;Kotsarenko et al, 2005). Ujihara et al (2004) observed highfrequency fluctuations in the northward and eastward electric and magnetic field measurements that are similar to the seismogram readings during the aftershocks of the May 2003 earthquake in Japan using a ground-based magnetotelluric equipment.…”

“…Ujihara et al, 2004;Iyemori et al, 2005;Kotsarenko et al, 2005). Ujihara et al (2004) observed highfrequency fluctuations in the northward and eastward electric and magnetic field measurements that are similar to the seismogram readings during the aftershocks of the May 2003 earthquake in Japan using a ground-based magnetotelluric equipment. Iyemori et al (2005) observed two geomagnetic pulsations during the 26 December 2004 Sumatra earthquake using ground-based magnetometers of Phimai in Thailand and Tong Hai in China.…”

Seismic dynamo effects associated with the M7.1 earthquake of 26 May 2003 off Miyagi Prefecture and the M6.4 earthquake of 26 July 2003 in northern Miyagi Prefecture, NE Japan

“…Since the finding of electric and magnetic field variations due to the so-called seismic dynamo effect in the case of the 1999 Izmit earthquake in northwestern Turkey (Honkura et al, 2000, we have tried to make magnetotelluric (MT) observations on various occasions Ujihara et al, 2004). In some cases, seismic observations were also made simultaneously with MT observations.…”

“…In fact, for small earthquakes, electric and magnetic signals due to the seismic dynamo effect were small and possible precursory signals should be much smaller than the noise level Ujihara et al, 2004).…”

Spectral peaks in electric field at resonance frequencies for seismically excited motion of ions in the Earth’s magnetic field

“…Pride and Morgan, 1991;Gershenzon, 1992;Pride, 1994;Pride and Haartsen, 1996;Haartsen and Pride, 1997;Garambois and Dietrich, 2002;Huang, 2002;Ren et al, 2010a, b). Appearance of unambiguous electric field changes was mostly synchronized with the arrival of seismic wave (Yamada and Murakami, 1982;Honkura et al, 2000Mogi et al, 2000;Nagao et al, 2000;Matsushima et al, 2002;Ujihara et al, 2004). Recently we proposed a new mechanism for electric field generation by seismic wave or more specifically by ground motion, based on some observational examples (Honkura et al, 2009).…”