Separation of Paleomagnetic Secular Variation Components: A Method and Its Application to a Sedimentary Record from Japan.

Itota, Chizu; Hyodo, Masayuki; Yaskawa, Katsumi

doi:10.5636/jgg.44.943

Cited by 6 publications

(12 citation statements)

References 24 publications

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“…motion is initiated from 5000 yr BP until 2000 yr BP, restricted to a direction perpendicular to the former motion. The same pattern of change in the constraining direction, by about 9W.5, and the existence of transitional motions have been observed in high-frequency field variations of Japanese data(Itota et al 1992). The only difference is that the transition in the Japanese data is dominated by a trochoidal motion in the counter-clockwise sense.Long-term features of drifting and standing non-(Plots of curvature of field motion paths versus age for the low-frequency field components.…”

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confidence: 54%

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Long-term features of drifting and standing non-dipole fields as determined from Holocene palaeomagnetic secular variations

Itota¹,

Hyodo²,

Yaskawa³

1997

Geophysical Journal International

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SUMMARY Geomagnetic field motions of Holocene secular variations are investigated using a separation method. The palaeomagnetic secular variations from Britain, North America and Australia have been subjected to maximum‐entropy method analyses. Based on the results of spectral analyses, the secular variations are separated by band‐pass filters into low‐frequency components, generally including the period band 1800‐3600 yr, and high‐frequency components, generally including the period band 1000‐1200 yr. There is an interval, from 4200 to 1700 yr BP, which shows clockwise rotational motions in the low‐frequency components of all three sites. Westward drifting of geomagnetic fields may be globally dominant. Swinging or elliptical looping motions constrained to a certain direction were observed in the low‐frequency components of the British data. The time duration for the persistence of the swinging motion constrained to a certain direction was 3500 years or so, which could be the lifetime of an oscillating stationary field. The duration of the transitional motion was 1000‐1300 years, which may indicate the recurrence time of a stationary field.

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confidence: 54%

“…the curvature of an age was obtained by averaging curvatures of three successive ages. The curvature plot for the Japanese low-frequency component whose band of periods is 1200-3500 yr (Itota et al 1992) is also shown in Fig. 6.…”

Section: Low-frequency Field Motionsmentioning

confidence: 98%

Long-term features of drifting and standing non-dipole fields as determined from Holocene palaeomagnetic secular variations

Itota¹,

Hyodo²,

Yaskawa³

1997

Geophysical Journal International

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“…After the work of Yukutake and Tachinaka (1968) and Evans (1984) this may be ascribed to the proximity of a stationary non-dipole source, such as the Mongolian anomaly, which grows and decays over time whilst maintaining the same polarity. An additional drifting non-dipole source passing the site may produce overall VGP motions with narrow elliptical segments (Itota et al, 1992). During the period 1.0 ka to 0.25 ka the VGP path follows an anticlockwise path suggestive of eastward drift of the non-dipole field in Xingwen during recent times.…”

Section: Palaeomagnetism Of the Xingwen Speleothemsmentioning

confidence: 99%

Speleothem Palaeosecular Variation Records from China: Their Contribution to the Coverage of Holocene Palaeosecular Variation Data in East Asia.

Openshaw¹,

Latham

Shaw³

1997

J. geomagn. geoelec

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Five stalagmitic speleothems from two caves in Sichuan province China, have yielded data on the palaeosecular variation (PSV) of the past 8.9 ka. The uranium-thorium disequilibrium method has been utilised in order to estimate the age of each record. Due to the high detrital load contributing some allogenic thorium, age corrections had to be applied to most sub-samples. The directional agreement between coeval central and lateral sub-samples where growth layers are horizontal and steeply dipping respectively suggests that inclination errors are absent in these speleothems. Correlation between features of declination and inclination in the individual records, even after time-averaging, are reasonable indicating a local consistency in recorded PSV and adding to the reliability of the palaeomagnetic and age data. Comparisons between our speleothem directions and the directions of the modern field drifted westward past our site at 0.13° yr-' suggests westward drifting of non-dipole sources during the past 2.8 ka. Using directional data from two speleothems with the longest growth periods a composite curve covering the past 8.9 ka has been constructed. The resulting VGP path again indicates predominantly westward drift. The declination and inclination features of these speleothems also compare reasonably with features of PSV in contemporaneous records from China and Japan.

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“…In their models, drifting of magnetic fields is constrained to longitudes from east Asia to the Americas. Detailed analyses of periodicity and field vector motions for the SV obtained in this study are described in ITOTA et al (1992).…”

Section: Geophysical Implicationsmentioning

confidence: 99%

Geomagnetic Secular Variation Reconstructed from Magnetizations of Wide-Diameter Cores of Holocene Sediments in Japan.

Hyodo

Itota

Yaskawa

1993

J. geomagn. geoelec

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A record of the secular variation of the geomagnetic field for the last 11000 years has been obtained from the remanent magnetization of seven wide-diameter (20 cm) cores of marine and lacustrine sediment from central to south-west Japan. Magnetization directions of five cores, possessing high-amplitude variations, exhibit good correlation. Two cores show lowamplitude variations, but they can be correlated well with other records after deconvolution to remove filtering effects of the post-depositional magnetization process. A composite secular variation curve was constructed by stacking the field direction records. Time constraints were obtained from radiocarbon ages of shell and wood fractions or tephrochronology. The secular variation curve agrees well with the archeomagnetic record after 1400 yrBP, with a slight difference in the time range 1400-2000 yrBP. The secular variation for the last 11000 years shows an elongated distribution of VGP's. The azimuth of the elongation, about 40°E, is consistent with that of VGP's from Japanese volcanic and sedimentary rocks during Brunhes epoch. The angular standard deviation is 14.5° (upper limit = 15.4°, lower limit = 13.7°). This estimate is slightly larger than that observed globally during Brunhes epoch and the position of the average VGP deviates 8.5° from the geographic north pole. These VGP analyses suggest a stationary nondipole source. The secular variation records from five northern hemisphere sites between 135°E and 95°W in longitude possess a single prominent feature: an extreme easterly swing in declination. A plot of age versus longitude of the swing at each site shows a clear westward drift, at a rate of about 0.13° /yr. The field vector around the swing represents clockwise looping at all the sites. This suggests that the swing is caused by a large non-dipole source which drifts at least from 135°E to 95°W in longitude.

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Separation of Paleomagnetic Secular Variation Components: A Method and Its Application to a Sedimentary Record from Japan.

Cited by 6 publications

References 24 publications

Long-term features of drifting and standing non-dipole fields as determined from Holocene palaeomagnetic secular variations

Long-term features of drifting and standing non-dipole fields as determined from Holocene palaeomagnetic secular variations

Speleothem Palaeosecular Variation Records from China: Their Contribution to the Coverage of Holocene Palaeosecular Variation Data in East Asia.

Geomagnetic Secular Variation Reconstructed from Magnetizations of Wide-Diameter Cores of Holocene Sediments in Japan.

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