Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
Search
Advanced search
OR
Browse
Search
Volume 34, Issue 7
Displaying 1-4 of 4 articles from this issue
Show all abstracts
    • |<
    • <
    • 1
    • >
    • >|
  • Identification of Mixing Frequency Components in the Geomagnetic Data from Kakioka, Japan, by Homomorphic Filtering Procedure
    Takashi OKUZAWA
    1982 Volume 34 Issue 7 Pages 423-430
    Published: 1982
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.34.423
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    Nonlinear process in the solar-terrestrial environment may produce mixing frequency components in the time series data of geomagnetic field. By applying the multiplicative homomorphic filtering to the analysis of geomagnetic data (H-component) taken at Kakioka, Japan, during IMS period, these frequency components have been isolated and identified with probable origins, i. e., solar rotation, lunar tide and unknown sources.
    View full abstract
    Download PDF (573K)
  • Thermal Processes of Titanomaghemite in Volcanic Rocks
    Yositugu INOUE
    1982 Volume 34 Issue 7 Pages 431-445
    Published: 1982
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.34.431
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    Detailed thermomagnetic, reflection microscopic and electron-probe microanalyzer studies of 27 selected, mostly andesitic rocks have indicated that partly maghemitized titanomagnetite decomposes at temperatures ranging from 200° to 600°C to ilmenite, ilmeno-hematite, and titanomagnetite forming intergrowths of exsolution lamellae. The unmixed phases are then homogenized to titanomagnetite at temperatures between 500° and 800°C.
    Difference in thermomagnetic curves in a cycle of heating and cooling between room temperature and 600°C is mostly owing to whether or not the mixing temperature is higher than 600°C. If the mixing proceeds in the thermomagnetic cycle, the Curie temperature observed in a cooling cycle is much lower than the initial value, since titanium content in titanomagnetite increases with mixing of ilmenite and ilmenohematite caused by heating.
    Size dependence of the mixing rate has also been revealed by thermal experiment with pulverized and separated specimens.
    View full abstract
    Download PDF (12673K)
  • Sondage Magnetotellurique Profond sur le Craton Ouest Africain (Republique de Haute-Volta)
    Esquisse de Modeles pour le Craton Ouest-Africain
    M. RITZ
    1982 Volume 34 Issue 7 Pages 447-452
    Published: 1982
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.34.447
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    A magnetotelluric sounding is carried out in the period band ranging from 15 to 10, 000sec on the West-African craton in the Upper Volta Republic. The site is located geologically on the Birrimian formations (2, 000m.y.). Bi-dimensional modelling suggests a conductive layer in the upper mantle at a depth of 130km. We have to assume a layer of high mantle resistivity, extending from 150 to at least 465km depth. An ultimate reduction to 10ohm-m occurs at 465km depth. Resistivity models for the West African craton are presented (Senegal-Upper Volta-Niger). They imply a general reduction in mantle resistivity between 80 and 130km. With these models we can find no crust-upper mantle transition from the viewpoint of resistivity. The upper mantle resistivity of 3, 000ohm-m may be taken as representative of the resistivity for the African Shield.
    View full abstract
    Download PDF (586K)
  • Conductivity Structure in and around Hokkaido, Japan as Revealed by the Period Dependence of the CA Transfer Functions
    Yasunori NISHIDA
    1982 Volume 34 Issue 7 Pages 453-465
    Published: 1982
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.34.453
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    The anomalies of geomagnetic variations in Hokkaido at a period of 5min are explained by the effect of the induction and the conduction currents within the surface layer such as the conducting sea and the sedimentary layer. However, the behaviour of the anomalies at longer periods than 5min is different in each region. From the model calculations to explain the period dependence of the CA transfer functions for each region, the following conclusions are drawn. The highly conducting layer (0.1S/m) exists at a likely depth range from 30 to 70km beneath the inner part of the Volcanic Front of the northeastern Japanese arc. On the contrary, the shallower part of the upper mantle beneath the outer part of the Volcanic Front seems to be poorly conducting (10-4S/m or so) though a quite thin and highly conducting layer may be present at a depth of about 130km. These results are consistent with other independent geophysical data such as heat flow and attenuation of seismic waves in and around Hokkaido.
    View full abstract
    Download PDF (1104K)
    • |<
    • <
    • 1
    • >
    • >|
feedback
 Top