Electric Anomalies Research Articles

Waste site modelling using a combination of electromagnetic induction and resistivity sounding measurements

Abstract The increasing number of sites assumed to be contaminated (e.g. in W. Germany over 42,000 at the time being) call for a prospecting method that effectively outlines their localizations and their 3D extensions. Electrical resistivity and electromagnetic induction (EMI) techniques are appropriate for such studies, since the waste materials generally cause electric anomalies. However, the often lateral heterogeneity of the hazardous sites distorts the measurements and therefore limits the capability for vertical modelling. To overcome this problem, an interpretation technique based on a combination of both methods has been developed. Application to an abandoned waste site in N. Germany shows good agreement between the results obtained here and those from the boreholes.

DETECTION OF AN AIR‐FILLED DRAINAGE GALLERY BY THE VLF RESISTIVITY METHOD1

AbstractVLF wave impedance measurements have been successfully used to detect air‐filled drainage galleries near the town of Alcala, Spain. The galleries are detectable by H‐polarization electric field measurements due to the electric field anomalies associated with the galleries and overlying gravel deposits. The forced deviation of the primary current flowlines around the 2D void results in a higher‐than‐normal apparent resistivity and a relative phase low above the gallery.The findings support earlier theoretical predictions that at very low frequencies (VLFs), galvanic current effects may dominate over vortex currents in moderately conductive terrains. Theoretical modelling confirmed that for a resistive target no detectable E‐polarization response can be expected from either magnetic or electric field measurements since current line deviations and vortex effects are negligible under such circumstances.The results demonstrate the importance of using at least two orthogonal VLF transmitters in order that anomalies arising from both galvanic and inductive effects may be identified, irrespective of orientation.

Positive holes in magnesium oxide. Correlation between magnetic, electric, and dielectric anomalies.

Magnetic susceptibility measurements of high purity MgO single crystals (<50-wt. ppm transition metals) by means of a vibrating-sample magnetometer shows an anomaly at 800 K. At the same temperature the electric conductivity increases anomalously, the static dielectric constant epsilon increases from 9 to approximately 150, a pronounced positive surface charge appears, and Fe2+ in the MgO matrix oxidizes to Fe3+. The data are consistent with O2(2-) (peroxy) defects, representing self-trapped, spin-paired positive holes at Mg2+ vacancy sites. Diamagnetic at low temperatures, the holes start to decouple their spins > 600 K, probably forming at first V0 centers (two O- at an Mg2+ vacancy), then V- centers (single O- at an Mg2+ vacancy), and releasing mobile O- states. These O- represent itinerant charge carriers on acceptor levels near the O 2p-dominated valence band and conduct by O- /O2- valency fluctuations. The O- concentration is of the order of 8 X 10(19) cm-3.

Thermal, electric and magnetic anomalies in the spin reorientation phase transitions of RE 2Fe 14B

A systematic study of the spin reorientation transitions in RE 2Fe 14B, RE = Nd, Ho, Er, Tm, Yb has been performed using magnetic ac susceptibility, heat-capacity and ac resistivity.

Electrotelluric forerunners to earthquakes in Kamchatka

Electrotelluric field (ETF) data observed at Shipunski-station (SPN), Kamchatka, were studied in detail for a period of 10 months, from August 1982 to June 1983. During this time interval seven large earthquakes, M ≥ 5.5, took place in the vicinity of Cape Shipunski, within 180 km of the SPN-station. A large earthquake, M = 5.7, took place on November 14, 1982. This event was preceded by a period of seismic quiescence of about 3 months and it took place at an epicentral distance of 74 km from SPN, in the oceanic part of the lithosphere. A striking change in the electrotelluric potential (ETP) data for November 8 is observed, 6 days before the occurrence of the earthquake. The change in the ETP is about 200 mV/km at a signal-to-noise ratio of roughly 4. The independent parallel line at SPN reveals the same anomalous ETP change, thus excluding instrumental and/or electrode effect. The possibility of a local source can be excluded after consideration of electric power sources in the area. On the other hand the ETF anomaly is rather similar to anomalies observed in Greece prior to the Kefallina earthquake of January 17, 1983. The ETF data are correlated with geomagnetic recordings from a station at Petropavlovsk (PRT), located about 90 km from Cape Shipunski. From the correlation of the two fields we conclude that the changes in the geomagnetic field cannot produce the sudden changes in the electric field if the electric conductivity is constant. Spectral analysis of the ETF data shows that the anomalies contain predominant periods of 24 h, 12 h, 8 h and 6 h, thus resembling the typical main spectral components of geomagnetic field changes. In spite of the apparent independent behaviour of the electric and geomagnetic fields during the anomalous period, we propose that electromagnetic induction is the primary cause of the electric anomaly, accompanied by rapid changes in the transfer functions between the two fields. This means changes in the electromagnetic induction after large, rapid changes of the resistivity in the fractured zone of the forthcoming earthquakes, initiated by the percolation of an interstitial fluid at a critical state of the fracturing process.

Electric and magnetic anomalies at the Atotsugawa fault and their implications for fault activity.

Observations of the geomagnetic total intensity, electric self-potential and surface resistivity were carried out at the Atotsugawa fault, a 60km long active fault of strike-slip type located in central Japan, in order to investigate the active fault structure and fault activity from electric and magnetic aspects. Notable anomalies were found along a measurement line selected in the central segment of the Atotsugawa fault. The anomalies are summarized as follows. The surface resistivity, as derived from VLF-MT, of the zone bounded on the north by one fault line and on the south by another is lower than that outside the zone. A very local anomaly in self-potential exists at the northern fault line which constitutes the northern boundary of the low resistivity zone. Inside this low resistivity zone exists a somewhat more resistive body. It should be highly magnetized as deduced from a magnetic anomaly amounting to about 600nT which was observed over the resistive body. The low resistivity zone seems to correspond to the fractured zone bounded by the two fault lines, and the northern one would be more active as implied by the self-potential anomaly which can be interpreted in terms of the electrokinetic effect associated with groundwater flow along the fault plane.

Electric and magnetic anomalies at the charge-density-wave transition in niobium-substituted vanadium diselenides

Electric and magnetic anomalies at the charge-density-wave transition in niobium-substituted vanadium diselenides

Electric and magnetic anomalies at the charge-density-wave transition in niobium-substituted vanadium diselenides

A systematic study has been made of the effect of niobium substitution on the CDW transition in VSe 2, especially in the low-doping region. Transitions were monitored by measurements of static magnetic susceptibility, which has been found to be particularly sensitive for both onset and lock-in discontinuities, and by measurements on resistivity and Hall effect. Results, discussed in terms of the model of Chan and Heine and in terms of McMillan's phenomenological model, suggest that structural changes due to the presence of the niobium dopant lead to enchanced electron-phonon coupling thus raising the CDW onset temperature.

Electrokinetic and magnetic anomalies associated with dilatant regions in a layered Earth

According to the dilatancy‐diffusion earthquake model, there will be fluid motion into a dilatant zone prior to an earthquake. One possible consequence of this fluid motion is the generation of an electric potential anomaly by means of electrokinetic processes. A surface electric potential anomaly will not be produced unless there is a boundary separating regions of differing streaming potential coefficient and there is a component of pressure gradient parallel to this boundary. The magnetic anomaly produced by the current flow is calculated. It is shown for the case of an n‐layered half space that the surface magnetic field will be identically zero no matter what the pressure distribution is. There will, however, be an azimuthal component of the magnetic field inside the earth.

Electric anomalies at the phase transition in FeS

The conductivity and thermoelectric power of single crystals of Fe 0.996S have been recorded at temperatures between 80° and 530°K. The material appears to be a p-type semiconductor with band-gap 0.04 eV at low temperatures and a not-well-behaved metal above the phase transition at T α≅420°K. A possible qualitative band model is discussed. There is a small sharp peak in the thermoelectric power at temperatures close to T α that we suspect to be the real origin of two reported apparently anomalous effects. They are: a voltage at T α, purportedly due to diffusion of free electrons at an interface between the low and high temperature phases, and a pyroelectric current with a sharp peak at T α. From symmetry considerations we show that the report by van den Berg of ferroelectricity in FeS below T α is unfounded.

Thermal Expansion and Electric Conductivity Anomalies in Cooled CuFeS2Films

Thermal Expansion and Electric Conductivity Anomalies in Cooled CuFeS₂Films

Аномалии теплового расширения и электропроводности в охлажденных пленках CuFeS&lt;sub&gt;2&lt;/sub&gt;

Аномалии теплового расширения и электропроводности в охлажденных пленках CuFeS&lt;sub&gt;2&lt;/sub&gt;

Investigation on earthquake prediction in Kamchatka

Investigations on earthquake prediction in Kamchatka are mainly carried out along three lines: 1. (1) The detailed investigations of Kamchatka-Komandorskiye Islands seismicity laws and long-term prediction (“seismic weather prediction”). The location of the Japanese earthquake on May 16, 1968, M = 7.9 was predicted well. 2. (2) The investigation of the connection between earthquakes and irregularities of electrotelluric field. The observed electric anomalies are found to arise some hours before the earthquakes and at the moment of the shock. The periods of such irregularities change from some minutes to half an hour. The amplitudes reach 50 mV/km. 3. (3) Investigations of velocities, amplitudes and other features of P-wave in the Pacific seismic focal zone near Kamchatka and their variations in time. Places of shot points and receivers at coast and in the ocean were constant. Distances were 40–200 km. Standard deviations of traveltime determinations were there ± 0.03 sec. In 1966–1968, when there were no earthquakes with M ≥ 6 in the investigated region, travel-time variations were in error limits. That means P velocities were constant here with an accuracy of 0.3–0.5%.

POSITIVE ANOMALIES OF THE NATURAL ELECTRIC FIELD ABOVE SULFIDE ORE BODIES

Origin of natural electric field anomalies, as well as their sign and intensity are determined by hydrological factors. As water level drops, depth of oxidation zone increases and fresh sulfides are encountered. Since the oxidation processes are more extensive in the upper part, the lowering of water table leaves fresh sulfides behind, and leads to the origin of positive natural field anomalies. ‐‐C. E. Sears, Jr.

Magnetocatalytic Effects and Electric Anomalies at the Néel Point of Nickel Oxide

Magnetocatalytic Effects and Electric Anomalies at the Néel Point of Nickel Oxide

THEORY AND PRACTICE OF LOW‐FREQUENCY ELECTROMAGNETIC EXPLORATION

Based directly on Maxwell’s Field Equations, the extremely low end of the frequency spectrum may be reduced in first approximation to simple potential theory. The approximation theory is borne out by some field experiments, the results of which are presented. Agreement with the theory, however, requires that the ground have a very large effective dielectric constant. This conclusion is supported by previous observations by a number of independent observers. Thus, the relaxation time has been found to be extremely great, not only in observations directly on the ground, but also in small samples of mud, and the sign of an electric anomaly over a relative insulator, such as crystalline salt or gas and oil, invariably has been found to be negative. Both of these observations can be explained in terms of a very great dielectric constant. The value yielded by the present experimental work is of the order of [Formula: see text].

The use of mathematics in the delineation of magnetic and electric anomalies

There appear to be two classes of magnetic anomalies—herein designated as (A) and (B).(A) Anomalies in which a large but finite number of consequent poles are to be found in the subsurface material, and for which there is a resultant equivalent magnet—This resultant magnet may have many forms, but in many cases a magnet of the form of a rectangular parallelopiped may be taken as the approximately equivalent magnet. Numerous deposits of magnetite, pyrrhotite, ilmenite, franklinite, and magnetic dikes are found to provide this condition. Moreover, it is frequently found that the magnetic meridian plane of these bodies has only a small declination from the Earth's magnetic meridian plane.