Remarks on Spatial Distribution of Long Period Variations in the Geomagnetic Field over European Area

Pěčová, Jana; Pêĉ, Karel; Praus, Oldřich

doi:10.5636/jgg.32.supplement1_si171

Cited by 4 publications

(5 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Rial et al (1984) report a distinct change in seismic structure at the northern boundary of the Alpine zone, which may correlate with the electrical results presented here. The analysis of the magnitude of the response at 27 days of Pecova, Praus & Pec (1980) also indicated a possible change in deep structure in this region. Table 2 lists the results of Johansen inversion of the data from all 17 stations.…”

Section: Resultsmentioning

confidence: 87%

The deep electrical structure of the Earth

Roberts

1986

Geophysical Journal International

View full text Add to dashboard Cite

Long-period estimates of the electromagnetic response of the Earth, which contain information about the variation of electrical conductivity at depth, are inverted to estimate the variation with depth of conductivity at depths between 300 and 1000 km beneath 17 locations which are scattered world-wide but concentrated in Europe. Two different onedimensional inversion techniques are used. The first is rather approximate but allows evaluation of the reliability of individual response estimates. The second is more mathematically rigorous, and allows estimation of conductivity depth-resolutions. The results from the two schemes are found to be qualitatively in agreement. The limited amount of data available, noise in the data, and approximations inherent in the inversion schemes used means that the results obtained are rather qualitative, but several rather clear results emerge from the analysis. The clearest and most significant of these is that there appear to be clear differences in the electrical structure at different places, even at great depth (hundreds of kilometres). The data from most locations indicate a marked increase in resistivity at a depth of 500-800 km. Within the central European area this decrease appears to lie rather deeper to the southeast than in the north-west, and to be underlain by material of higher resistivity. This secondary increase in resistivity is not seen in data from other parts of the world. The deep oceanic mantle may be more conductive than the continental mantle at corresponding depths. The depth to the well-known rapid rise in conductivity which lies at a depth of about 500 km seems too deep for this feature to be associated with the 400 km seismic discontinuity. It is in fact difficult to associate this feature with any specific seismic feature.

show abstract

Section: Resultsmentioning

confidence: 87%

The deep electrical structure of the Earth

Roberts

1986

Geophysical Journal International

View full text Add to dashboard Cite

show abstract

“…A relationship between conductosphere depths and latitude has earlier been reported for the European (Pecova et al, 1980) and North American (Petersons and Anderssen, 1990) regions. While Petersons and Anderssen (1990) considered the decrease in depth of conductosphere with increase in latitude at any given period to be a characteristic of the real Earth, Pecova et al (1980) attributed these gradients to be indicative of some deep E-W striking feature below central Europe. Though the depths obtained for the Indian region might first suggest a latitudinal dependence, the differences in the depth estimates are in fact negligible, when compared with the error estimates at individual sites, and so do not permit such an interpretation of these data for the Indian region.…”

Section: Lateral Variation In the Depth Of The Conductospherementioning

confidence: 99%

“…This objective is accomplished by determining robust single-station EM responses, following a statistical test for the validity of the P 0 1 character of the data. Depth estimates obtained for 27-day period are discussed in the light of their dependency with latitude, and compared with earlier results (Pecova et al, 1980;Petersons and Anderssen, 1990). After augmenting the response estimates with those of Sq analysis obtained from the same data sets, the geo-electrical structure for the Indian region is discussed and compared with other regional models.…”

Section: Introductionmentioning

confidence: 99%

“…In most of the earlier works, the validity of the P 0 1 approximation for the inducing field has been assumed, rather than demonstrated (for e.g., Pecova et al, 1980;Petersons and Anderssen, 1990;Chen and Fung, 1991). In the present work, in view of the availability of continuous and uninterrupted data from the chosen observatory network (Fig.…”

Section: Test For P 0 1 Cos(θ) Dependence Of the Inducing Source Fieldmentioning

confidence: 99%

See 1 more Smart Citation

Geo-electrical structure of the mantle beneath the Indian region derived from the 27-day variation and its harmonics

Chandrasekhar

2014

Earth Planet Sp

View full text Add to dashboard Cite

Estimates of the C-response function were determined by Z : H method to obtain conductivity and depth values for a substitute perfect conductor (conductosphere) beneath the Indian region, utilizing geomagnetic variations at periods of 27-day and its harmonics. Two and half years of continuous geomagnetic data were utilized. These data were recorded during 1975-77, at a chain of 13 stations confined to the 150 0 geomagnetic longitude band, which extended from the dip-equator at the southern tip of India, to the northern parts of Russia. Complex demodulation technique was employed to determine the electromagnetic (EM) responses. Taking advantage of the dense latitudinal distribution of the observatories, the demodulates of all the stations were tested statistically to check the validity of the P 0 1 approximation for the inducing field. Single-station response estimates, for a 27-day period, computed by a robust method have shown that reliable EM responses (consistent with P 0 1 source dependence and with local 1-D Earth structure) could be obtained for only 6 stations, all situated in the mid-latitude region. The depth estimates at all 6 stations are consistent, including Sabhawala (SAB) which is situated close to the Himalayan collision zone. The negligible differences in the depth estimates of these mid-latitude stations do not show any latitudinal dependence, as against such an observation reported for the European and the North American regions. The mean depth of the conductosphere is found to be 1200 (±200) km, with an average conductivity of 0.7 (±0.3) S/m. Comparison of the mean geo-electrical structure with those of other regional models shows that the presence of a mid-mantle conductor at 850 km depth could be considered to be a global phenomenon.

show abstract

“…The examples can be found in Banks (1969), Pecova, et al (1980), Chen and Fung (1991 ), Chandrasekhar and Arora (1996). The inducing period is longer than 24 h. The main source field variations longer than 24 h are those of 27 d and its harmonics, half-year and one year.…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic response function for the semi-annual variations estimated by the single-station method using the night-time values of the geomagnetic fields

Chen

2000

Acta Seimol. Sin.

View full text Add to dashboard Cite

The geomagnetic night-time values were used to estimate the electromagnetic response function Q~ for half-year period. [f the spatial structure of the source field can be described by the P~" approximation, one can estimate the Qt value using tbe single-station Z/H method. This technique enables us to carry out regional deep geomagnetic sounding by the method. The data used tbr analyses are geomagnetic night-time values for about, typically, 26 years from 5 good-quality stations and for several years from 34 stations distributed over the globe. The results indicate that the night-time values yield more reliable response estimates for half-year period compared to the usual estimates obtained from daily means. It implies that the Pt" approximation for the night-time fields holds good for the half-year period, but the daily means are not suitable for estimating the response function of the semi-annual variations by using the single-station method. Source field analyses for daily means data and night-time means data have also been carried out in this paper.

show abstract

Remarks on Spatial Distribution of Long Period Variations in the Geomagnetic Field over European Area

Cited by 4 publications

References 3 publications

The deep electrical structure of the Earth

The deep electrical structure of the Earth

Geo-electrical structure of the mantle beneath the Indian region derived from the 27-day variation and its harmonics

Electromagnetic response function for the semi-annual variations estimated by the single-station method using the night-time values of the geomagnetic fields

Contact Info

Product

Resources

About