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Volume 26, Issue 5
Displaying 1-7 of 7 articles from this issue
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James R. WAIT, Kenneth P. SPIES1974 Volume 26 Issue 5 Pages 449-458
Published: 1974
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSAdopting an idealized two-dimensional model, we consider the electromagnetic fields existing in a crustal layer that has any number of homogeneous segments with vertical interfaces. The magnetic field vector is everywhere parallel to these interfaces and to the earth's surface. Using a quasi-static approach, expressions for the electric fields at the earth's surface are derived and calculations for the actual surface impedance are then presented. It is shown that the vertical contacts will cause strong perturbations of the surface impedance calculated on the basis of a locally uniform slab model. This could be an important factor in carrying out the interpretation of magneto-telluric data.View full abstractDownload PDF (683K) -
A. I. I. ETTE, C. O. OLUWAFEMI1974 Volume 26 Issue 5 Pages 459-465
Published: 1974
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSInvestigations of the diurnal variations and “agitations” of the horizontal electric field, based on continuous registrations of the horizontal electric potential difference between closely spaced radioactive probes, show that the variations and “agitations” result from the advection of natural space charge over the probes. Since the horizontal field is wind-aligned and space-charge dependent, there is invariably poor correlation in the registrations of two probes lined up in the wind direction.View full abstractDownload PDF (474K) -
B. R. ARORA, G. K. RANGARAJAN1974 Volume 26 Issue 5 Pages 467-474
Published: 1974
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSAmplitudes and phases of the annual and semiannual components in the geomagnetic disturbance field and its constituents are derived at each local hour of the day for Alibag and Hermanus. The annual variations at Alibag and Hermanus are nearly in phase. The variations at the same station for intervals 12hr apart are nearly in phase opposition. It is shown that the local time variation in the annual component is predominantly due to the modulation in the asymmetric part (SD) and that in semiannual component is due primarily to the symmetric part (DR) of the disturbance field. The semiannual modulation of symmetric and asymmetric parts of the disturbance field are in phase opposition during morning hours and in phase in the evening hours leading to a marked forenoon/evening asymmetry in its amplitude. The results obtained here explain the local time variation in annual and semiannual modulations of horizontal intensity derived from observations on all days earlier by BHARGAVA (1972b, c).View full abstractDownload PDF (816K) -
V. A. SCHMIDT1974 Volume 26 Issue 5 Pages 475-486
Published: 1974
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSA modified Eulerian orthogonal transformation is extremely useful in transforming the magnetization vector of a rock sample from the sample coordinate system as measured in a magnetometer to the ancient coordinate system at the sampling site, especially if complicated folding has occurred since the rock was magnetized. The method is adaptable to a wide variety of sample collecting and marking conventions. The form and function of the transformation, which has been widely used in other fields, is reviewed and is applied to the following situations of interest in paleomagnetism: transformation from sample to site coordinates; transformation of sample coordinates if the reference or marking plane is oblique to the sample coordinate system; and removal of the effects of horizontal or plunging folds. An earlier treatment of this latter problem by ZOTKEVICH (1972) is shown to be incorrect. Additional applications of the transformation are made to the display of paleomagnetic data. The transformation has many potential applications in structural geology.View full abstractDownload PDF (1157K) -
Charles R. DENHAM1974 Volume 26 Issue 5 Pages 487-498
Published: 1974
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSPaleomagnetic directions from two sites at Mono Lake, California, 24000 years ago traced-out a well-defined counter-clockwise loop 25° in diameter. Major features of the loop can be explained by an inward directed radial dipole located at 0.5 Earth's radius, drifting eastward along a path 15° south of Mono Lake. Its longitudinal velocity was 0.10-0.19°/yr and its strength was 0.12-0.21 relative to the Earth's main dipole moment. The life-span of this perturbing source probably was similar to the period of the magnetic loop, about 850 years.View full abstractDownload PDF (1327K) -
F. HELLER, R. EGLOFF1974 Volume 26 Issue 5 Pages 499-509
Published: 1974
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSStable remanent magnetization of a granite-aplite dyke forms stripes of normal and reversed polarity. Phenomenological evidence suggests that the different polarities are caused by self-reversal of ilmenohematite, the carrier of stable remanence. Thermal experiments show an ‘imperfect’ self-reversal which is based on the presence of two interacting phases with different Curie points within the exsolved ilmenohematite. Perfect self-reversal of natural remanent magnetization may have occurred during the original slow cooling of the granite-aplite dykes which, below the blocking temperature, obviously have the same cooling history as the main Bergell granite massif.View full abstractDownload PDF (1038K) -
Akira IWATA, Haruji ISHIKAWA1974 Volume 26 Issue 5 Pages 511-514
Published: 1974
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSDownload PDF (377K)
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