ULF magnetic emissions connected with under sea bottom earthquakes

Abstract

Abstract. Measurements of ULF electromagnetic disturbances were carried out in Japan before and during a seismic active period (1 February 2000 to 26 July 2000. A network consists of two groups of magnetic stations spaced apart at a distance of ≈ 140 km. Every group consists of three, 3-component high sensitive magnetic stations arranged in a triangle and spaced apart at a distance of 4-7 km. The results of the ULF magnetic field variation analysis in a frequency range of F = 0.002−0.5 Hz in connection with nearby earthquakes are presented. Traditional Z/G ratios (Z is the vertical component, G is the total horizontal component), magnetic gradient vectors and phase velocities of ULF waves propagating along the Earth's surface were constructed in several frequency bands. It was shown that variations of the R(F ) = Z/G parameter have a different character in three frequency ranges: F 1 = 0.1 ± 0.005, F 2 = 0.01 ± 0.005 and F 3 = 0.005 ± 0.003 Hz. Ratio R(F 3 )/R(F 1 ) sharply increases 1-3 days before strong seismic shocks. Defined in a frequency range of F 2 = 0.01 ± 0.005 Hz during nighttime intervals (00:00-06:00 LT), the amplitudes of Z and G component variations and the Z/G ratio started to increase ≈1.5 months before the period of the seismic activity. The ULF emissions of higher frequency ranges sharply increased just after the seismic activity start. The magnetic gradient vectors (∇B ≈ 1 − 5 pT/km), determined using horizontal component data (G ≈ 0.03 − 0.06 nT) of the magnetic stations of every group in the frequency range F = 0.05 ± 0.005 Hz, started to point to the future center of the seismic activity just before the seismoactive period; furthermore they continued following space displacements of the seismic activity center. The phase velocity vectors (V ≈ 20 km/s for F = 0.0067 Hz), determined using horizontal component data, were directed from the seismic activity center. Gradient vectors of the vertical component pointed to the closest seashore (known as the "sea shore" effect). The location of the seismic activity centers by two gradient vectors, conCorrespondence to: V. S. Ismaguilov (galina@gh5667.spb.edu) structed at every group of magnetic stations, gives an ≈10 km error in this experiment.

Investigation of ULF magnetic anomaly during Izu earthquake swarm and Miyakejima volcano eruption at summer 2000, Japan

“…Numerous advanced studies including the recent ones (Ismaguilov et al, 2001;Hattori et al, 2002;Smirnova et al, 2004) prove the reliability of some applied algorithms and data processing techniques. In addition to that, the ULF part of electromagnetic emission, generated by the earthquake, can be recorded at the Earth's surface by modern magnetometers without significant attenuation if they are generated at typical earthquake nucleation depths (∼10 km).…”

“…Different long-term observatories are already in operation in Japan (Hayakawa, et al, 1996;Uyeda et al, 2000), Russia (Ismaguilov et al, 2001), Greece (Varotsos et al, 1996), U.S. (Fraser-Smith, et al, 1990) …”

Pre-earthquake signals – Part II: Flow of battery currents in the crust

“…If large volumes of rocks subjected to increasing stresses deep in the Earth's crust generate powerful current pulses, those pulses will lead to bursts of low frequency electromagnetic (EM) radiation. Though we are still a long way from understanding the details of the current flow, we are gaining insight into the basic physical process that can explain low-frequency EM emissions widely reported both on account of satellite and ground station data (Biagi et al, 2001;Dea et al, 1997;Eftaxias et al, 2003;Enomoto et al, 2006;Ismaguilov et al, 2001;Kushwah et al, 2005;Ohta et al, 2001;Parrot, 1994;Parrot et al, 2006).…”

A new method to study the time correlation between Van Allen Belt electrons and earthquakes

“…Furthermore, only continental earthquakes are retained, excluding those in the oceanic crust (Oike and Ogawa 1986;Galper et al 1989;Parrot 1994), although the absorption of EME waves in the oceanic water is questionable (Ismaguilov et al 2001). …”