On the nature of steady short-period oscillations of the earth's magnetic field /Pc3 and Pc4/

Investigation of steady short period type-Pc3 and Pc4 geomagnetic field oscillation

Certain peculiarities in the distribution of plasma concentration and of the field of Alfven waves in the earth's magnetosphere

Peculiarities in plasma density and Alfven wave velocity in magnetospher

Variations of phase velocity and gradient values of ULF geomagnetic disturbances connected with the Izu strong earthquakes

Results of study of anomaly behavior of amplitudes, phase velocities and gradients of ULF electromagnetic disturbances (<i>F</i> = 0.002 – 0.5 Hz) before and during a seismic active period are presented. Investigations were carried out in Japan (Izu and Chiba peninsulas) by two groups of magnetic stations spaced apart at a distance ~ 140 km. Every group (magnetic gradientometer) consists of three 3-component high sensitive magnetic stations arranged in a triangle and spaced apart at distance 4–7 km. Kakioka magnetic station (>200 km to the North from Izu) was used as a reference point. Available data (only night-time intervals 00:00–07:00 LT) were preliminary filtrated by narrow pass-band filters (16 frequency bands – periods <i>T</i> = 2–512 s). The amplitude, gradient and phase velocity values and probabilities of directions of gradient and phase velocity vectors were constructed for the every frequency band. Apparent resistivities of the Earth’s crust in the every frequency band were calculated using the phase velocity values. It was found that Z component amplitudes of the ULF magnetic disturbances increased at Izu peninsula 2–4 weeks before the seismic active period and 2–4 days before the strongest seismic shocks (<i>M</i> > 6). Ratio of Z component amplitudes of Kamo (Izu) and Kakioka data (<i>Z_k</i>/<i>Z_kk</i>) increased during 2–4 weeks before the seismic activity start (27 June 2000) and reached a maximum just before a moment of the strongest seismic shock (EQ with <i>M</i> = 6.4). The gradient and the phase velocity values had an anomaly behavior during the same 2–4 weeks before the start of seismic active period. The gradient vectors of the total horizontal component of the ULF magnetic pulsations were probably directed to the regions with increased conductivity. New additional direction of the gradient vectors appeared 2–3 weeks before the seismic activity start – the direction to the seismic active area which appeared due to a magma rising

ULF magnetic emissions connected with under sea bottom earthquakes

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 &#x2248;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 <i>F</i> = 0.002–0.5 Hz in connection with nearby earth-quakes are presented. Traditional <i>Z</i>/<i>G</i> ratios (<i>Z</i> is the vertical component, <i>G</i> 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 <i>R</i>(<i>F</i>) = <i>Z</i>/<i>G</i> parameter have a different character in three frequency ranges: <i>F</i>₁ = 0.1 ± 0.005, <i>F</i>₂ = 0.01 ± 0.005 and <i>F</i>₃ = 0.005 ± 0.003 Hz. Ratio <i>R</i>(<i>F</i>₃)/<i>R</i>(<i>F</i>₁)</i> sharply increases 1–3 days before strong seismic shocks. Defined in a frequency range of <i>F</i>₂ = 0.01 ± 0.005 Hz during nighttime intervals (00:00–06:00 LT), the amplitudes of <i>Z</i> and <i>G</i> component variations and the <i>Z</i>/<i>G</i> ratio started to increase &#x2248; 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>&#x2207; <i>B</i></b> &#x2248; 1 – 5 pT/km), determined using horizontal component data (<i>G</i> &#x2248; 0.03 – 0.06 nT) of the magnetic stations of every group in the frequency range <i>F</i> = 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 (<i>V</i> &#x2248; 20 km/s for <i>F</i> = 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, constructed at every group of magnetic stations, gives an &#x2248; 10 km error in this experiment

Electro-Magnetic Earthquake Bursts and Critical Rupture of Peroxy Bond Networks in Rocks

We propose a mechanism for the low frequency electromagnetic emissions and other electromagnetic phenomena which have been associated with earthquakes. The mechanism combines the critical earthquake concept and the concept of crust acting as a charging electric battery under increasing stress. The electric charges are released by activation of dormant charge carriers in the oxygen anion sublattice, called peroxy bonds or positive hole pairs (PHP), where a PHP represents an $O_3X/^{OO}\backslash YO_3$ with $X,Y = Si^{4+}, Al^{3+}...$, i.e. an $O^-$ in a matrix of $O^{2-}$ of silicates. We propose that PHP are activated by plastic deformations during the slow cooperative build-up of stress and the increasingly correlated damage culminating in a large ``critical'' earthquake. Recent laboratory experiments indeed show that stressed rocks form electric batteries which can release their charge when a conducting path closes the equivalent electric circuit. We conjecture that the intermittent and erratic occurrences of EM signals are a consequence of the progressive build-up of the battery charges in the Earth crust and their erratic release when crack networks are percolating throughout the stressed rock volumes, providing a conductive pathway for the battery currents to discharge. EM signals are thus expected close to the rupture, either slightly before or after, that is, when percolation is most favored.Comment: 17 pages with 3 figures, extended discussion with 1 added figure and 162 references. The new version provides both a synthesis of two theories and a review of the fiel

A possible model for initiationof ULF oscillation in magma

During the period just prior to an earthquake, an electomagnetic emission develops over seismic zones. In this paper, a model of excitation of magnetic fields over zones of volcanic activity is proposed. Movement of magma along volcanic channels precedes an earthquake, hydrodynamic processes in the moving magma can lead to formation of waves and vortices in the flow which, in turn, can cause development of magnetic fields in conducting magma. During this period, the movement of the magma intensifies leading to a corresponding intensification of the magnetic fields. In this paper, different possible sources of ULF pulsation in magma are examined,and the variable geomagnetic fields induced by this pulsation are estimated.PublishedJCR Journalope

Fluid systems of the Mamsko-Bodaibin mineragenic zone in north Transbaikal

The article presents the results of the study of fluid systems in the Earth’s crust within the Mamsko-Bodaibin mineragenic zone of the northern Transbaikal using magnetic field anomalies, gravity and seismic data. Two-dimensional models of the density and magnetization of schistosity zones and deep sections of gold deposits allowed us to identify the location of fluid systems and possible paths of magmatic thermofluid flows in ancient rocks. The authors have revealed peculiarities of fluid systems at different depth levels and the role of vertical ore-controlling formations of the earth crust of the Mamsko-Bodaibin zone. Diagnostic features are proposed to control the paths of fluid transport to the surface and the location of the ore-generating structures, taking into account the fluid-magmatic activity of the earth’s crust and mantle. The analysis showed that the Mamsko-Bodaibin zone is prospective in the search for new ore objects. Based on the results of the study, we propose a refined model of the ore localization of the Sukholozhskoye ore field, which includes the influence of deep factors

A possible model for initiationof ULF oscillation in magma

During the period just prior to an earthquake, an electomagnetic emission develops over seismic zones. In this paper, a model of excitation of magnetic fields over zones of volcanic activity is proposed. Movement of magma along volcanic channels precedes an earthquake, hydrodynamic processes in the moving magma can lead to formation of waves and vortices in the flow which, in turn, can cause development of magnetic fields in conducting magma. During this period, the movement of the magma intensifies leading to a corresponding intensification of the magnetic fields. In this paper, different possible sources of ULF pulsation in magma are examined,and the variable geomagnetic fields induced by this pulsation are estimated