Inductive seismo-electromagnetic effect in relation to seismogenic ULF emission

International audienceDuring the seismic wave propagation through the crust, the electromagnetic pulse can originate due to MHD conversion in this conductive medium. On the assumption of simple models of seismic wave excitation and attenuation, the problem is reduced to the analysis of a diffusion-like equation for a vector potential function. In this way, we need to change the classical gauge condition. A semi-analytical form of the solution is obtained in a case with constant ground conductivity. Dependencies of the electric and magnetic field components and the pulse duration on distance and crust conductivity have been computed in detail. The results could be useful for the explanation of electromagnetic signals related to coseismic, foreshock and aftershock activity

VLF/LF sounding of the lower ionosphere to study the role of atmospheric oscillations in the lithosphere-ionosphere coupling

It is shown that sounding of the lower ionosphere boundary by subionospheric signals from powerful VLF/LF transmitters can be a useful tool for the investigation of Planetary Waves (PW) with periods in a range of 2-30 days. A specific spring-time transition in the PW dynamic periodograms is revealed from our analysis of several years data using Tsushima, Japan VLF transmitter (10.2kHz) along the path with length of about 1000km. Earthquake influence m the periodograms could be sometime recognized as an appearance of specific wavelets. We discuss a possibility of PW transportation from the bottom to the upper atmosphere as modulation of shorter-scale gravity waves (GW) inside the troposphere and subsequent demodulation of the GW at the atmosphere-ionosphere boundary for the explanation of observational results. The existence of modulation due to gravity waves in LF signal amplitude is presented to support the above hypothesis

A direction finding technique for the ULF electromagnetic source

International audienceA technique of direction finding is proposed, which can be applied to the magnetic-dipole type source located in the conductive ground. To distinguish a weak ULF source signal from the natural noise a network of multicomponent magnetometers is supposed to be used. The data obtained by the ground-based stations is processed in such a way that a set of partial derivatives of the magnetic perturbations due to the source are found. Comparing these derivatives with theoretical formulae makes it possible, in principle, to find the ULF source parameters such as the distance and amplitude. Averaging the data and a special procedure are proposed in order to exclude random fluctuations in the magnetic moment orientation and to avoid hydrogeological and other local factors

Low-latitude ionospheric turbulence observed by Aureol-3 satellite

Using PSD (Power Spectral Density) data on electron density and electric field variations observed on board Aureol-3 satellite at low-to-mid-latitude ionosphere we analyze a scale distribution of the ionospheric turbulence in a form <i>k<sup>-α</sup></i>, where <i>k</i> is the wave number and α is the spectral index. At first, high-resolution data in the near-equator region for several orbits have been processed. In this case the frequency range is from 6Hz to 100Hz (corresponding spatial scales from 80m to 1.3km), each power spectrum obeys a single power law fairly well, and the mean spectral indices are rather stable with α<sub><i>N</i></sub>=2.2±0.3 and α<sub><i>E</i></sub>=1.8±0.2, for the density and electric field, respectively. Then we produce a statistical study of 96 electric field bursts in the frequency range 10-100Hz from low-time resolution data (filter bank envelope). These bursts concentrate on the side of the Equatorial Anomaly crest (geomagnetic latitude 30-40°). Spectral indices of the bursts vary in the interval α<sub><i>E</i></sub>=2.0-2.5 but are fairly stable in seasons and local times. The electric field power of the burst has rather a large variability but has a relative increase in mean values for the summer and winter, as well as the daytime. The effect of major seismic activities toward the ionospheric turbulence is not conclusive either for the refractive index or for the electric field power. However, the mean value for the electric field power of bursts during seismic periods is larger than that for non seismic periods, and the statistical difference of the mean values is rather significant

Anomalies of LF signal during seismic activity in November?December 2004

International audienceA signal transmitted by Japan Time Standard LF station (40 kHz, Fukushima prefecture) and recorded in Petropavlovsk-Kamchatski (Russia) is analyzed during a time interval from 1 July 2004 till 24 January 2005. This interval is characterized by quiet seismic conditions up to the beginning of November, but rather strong seismic activity occurs in November and December not far from Hokkaido (Japan) and in the region of northern Kuril Islands. There were three series of earthquakes with M=5.6?7.1 in a zone of sensitivity of our wave path during two months. Nighttime "bay-like" phase and amplitude anomalies of the LF signal are observed several days before and during every series of earthquakes. During the whole period of seismic activity a significant shift in terminator times is also evident. The spectrum of LF seismo-induced anomalies shows a clear increase for the period of about 25 min

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

Depression of the ULF geomagnetic pulsation related to ionospheric irregularities

We consider a depression in intensity of ULF magnetic pulsations, which is observed on the ground surface due to appearance of the irregularities in the ionosphere. It is supposed that oblique Alfven waves in the ULF frequency range are downgoing from the magnetosphere and the horizontal irregularities of ionospheric conductivity are created by upgoing atmospheric gravity waves from seismic source. Unlike the companion paper by Molchanov et al. (2003), we used a simple model of the ionospheric layer but took into consideration the lateral inhomogeneity of the perturbation region in the ionosphere. It is shown that ULF intensity could be essentially decreased for frequencies f = 0.001-0.1 Hz at nighttime but the change is negligible at daytime in coincidence with observational results

Notes on Stein-Sahi representations and some problems of non L2L^2 harmonic analysis

We discuss one natural class of kernels on pseudo-Riemannian symmetric spaces.Comment: 40p

Observables and a Hilbert Space for Bianchi IX

We consider a quantization of the Bianchi IX cosmological model based on taking the constraint to be a self-adjoint operator in an auxiliary Hilbert space. Using a WKB-style self-consistent approximation, the constraint chosen is shown to have only continuous spectrum at zero. Nevertheless, the auxiliary space induces an inner product on the zero-eigenvalue generalized eigenstates such that the resulting physical Hilbert space has countably infinite dimension. In addition, a complete set of gauge-invariant operators on the physical space is constructed by integrating differential forms over the spacetime. The behavior of these operators indicates that this quantization preserves Wald's classical result that the Bianchi IX spacetimes expand to a maximum volume and then recollapse.Comment: 23 pages, ReVTeX, CGPG-94/6-3, UCSBTH-94-3