Publikationsdatum:
1992-01-01
Beschreibung:
A new method is introduced to analyze paleosecular variations of the earth's magnetic field direction. The method consists of the following four steps. First, a time series of a pair of declination and inclination is transformed into two components defined in ADF reference frame. Second, characteristic periods are estimated with a spectral analysis. Third, the secular variation components of the periods are separated through band-pass filters. Finally, the motion of field vectors is investigated with respect to its curvature on a polar projection for each secular variation component. The present method has been applied to the sedimentary secular variation record from central and southwest Japan for the last 12000 years. The results indicate two main periodic motions of field vectors with the periods of about 700 and 2350 years. The 2350 years component is dominated by smooth clockwise motions. This suggests that the westward drifting field has persisted almost steadily for the last 12000 years. However, the breakup of the clockwise motion took place between 4500 and 8100 years B. P., which may have been generated by an accidental temporary standing field. The 700 years component is characterized by the thin elliptic motion whose major axes remained almost constant during more than 1750 years long and rotational sense changed frequently. This elliptic motion may have been caused by intensity changes in standing fields added with week drifting fields. © 1992, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.
Print ISSN:
0022-1392
Thema:
Geologie und Paläontologie
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