Intensity of the Earth's Magnetic Field in Geological Time

Kono, Michikata

doi:10.5636/jgg.23.1

Cited by 36 publications

(32 citation statements)

References 16 publications

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“…For example, Kono and Tanaka (1995) found jmj ¼ 7:4AE 4:3 Â 10 22 Am 2 . However, more recent estimates are significantly lower than this.…”

Section: The Dipole Moment Through Geologic Timementioning

confidence: 99%

“…A survey by Kono and Tanaka (1995) of intensity measurements on rocks between 100 and 3,500 Ma shows evidence for moment strength fluctuations on roughly 1,000 Ma time scales, but little or no evidence of a secular trend. Overall, their study found dipole moments generally lower than, but within a factor of 2, its present-day value for most of that time.…”

Section: The Dipole Moment Through Geologic Timementioning

confidence: 99%

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Changes in earth’s dipole

Olson

Amit

2006

Naturwissenschaften

139

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The dipole moment of Earth's magnetic field has decreased by nearly 9% over the past 150 years and by about 30% over the past 2,000 years according to archeomagnetic measurements. Here, we explore the causes and the implications of this rapid change. Maps of the geomagnetic field on the core-mantle boundary derived from ground-based and satellite measurements reveal that most of the present episode of dipole moment decrease originates in the southern hemisphere. Weakening and equatorward advection of normal polarity magnetic field by the core flow, combined with proliferation and growth of regions where the magnetic polarity is reversed, are reducing the dipole moment on the core-mantle boundary. Growth of these reversed flux regions has occurred over the past century or longer and is associated with the expansion of the South Atlantic Anomaly, a low-intensity region in the geomagnetic field that presents a radiation hazard at satellite altitudes. We address the speculation that the present episode of dipole moment decrease is a precursor to the next geomagnetic polarity reversal. The paleomagnetic record contains a broad spectrum of dipole moment fluctuations with polarity reversals typically occurring during dipole moment lows. However, the dipole moment is stronger today than its long time average, indicating that polarity reversal is not likely unless the current episode of moment decrease continues for a thousand years or more.

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“…For example, Kono and Tanaka (1995) found jmj ¼ 7:4AE 4:3 Â 10 22 Am 2 . However, more recent estimates are significantly lower than this.…”

Section: The Dipole Moment Through Geologic Timementioning

confidence: 99%

Section: The Dipole Moment Through Geologic Timementioning

confidence: 99%

Changes in earth’s dipole

Olson

Amit

2006

Naturwissenschaften

139

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“…and K-Ar Ages of Successive Lava Flows (4)* -K-Ar Ages of the Usami Volcano, Izu Peninsula, Japan- (Received May 25, 1970) Paleomagnetic study of Pleistocene andesites from the Usami Volcano, Izu Peninsula has been carried out and it is reported that the upper and the lower lava flows are normally magnetized, whereas the middle flows have reversed NRM (Nagata et al ., 1957: Kono, 1968. The geology and petrology of volcanic rocks in this area have been investigated by Kuno (1950Kuno ( , 1951.…”

Section: Paleomagnetismmentioning

confidence: 99%

“…They are UV08, UV10, UV12 and UV14. Details of geological settings for these samples were described by Kono (1968).…”

Section: Paleomagnetismmentioning

confidence: 99%

Paleomagnetism and K-Ar Ages of Successive Lava Flows (4)

Kaneoka

Ozima

Kuno

1970

J. geomagn. geoelec

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“…In this study, in situ paleomagnetic directions are used to estimate the true sense and amount of tectonic deformation recorded in volcanic rocks. Several paleomagnetic studies were made on the Quaternary volcanics mainly in the northeastern to middle eastern Izu Peninsula and revealed that counterclockwise deflections of declination up to several tens of degrees commonly exist in this area, such as in Taga Volcano (NAGATA et al, 1957), Usami Volcano (KoNo, 1968;KOYAMA, 1981), Tenshi and Amagi Volcanoes (KOYAMA, 1986). The declination deflection in the Usami Volcano was explained by local deformations along a large strike-slip fault (KOYAMA,1981).…”

Section: Introductionmentioning

confidence: 99%

Paleomagnetism of Quaternary volcanics in the Izu peninsula and adjacent areas, Japan, and its tectonic significance.

Kikawa

Koyama

Kinoshita

1989

J. geomagn. geoelec

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A paleomagnetic investigation was made on the Quaternary volcanics in the Izu Peninsula and the adjacent Ashitaka and Izu-Oshima areas located on the northern tip of the Philippine Sea plate, central Japan. This study evaluates the deformation associated with the collision of the Izu block with Honshu. About 900 volcanic rock samples ranging in age from 0.2 to 1.5 Ma were measured. Alternating field demagnetization indicates that these samples have stable natural remanent magnetizations. Fine grained titanomagnetite was identified as the carrier of the remanent magnetizations by thermomagnetic analysis and microscopic observation. The paleomagnetic directions from both Ashitaka Volcano and Izu-Oshima island, which are located to the north and to the east of the Izu Peninsula, respectively, are not significantly different from that of the present axial geocentric dipole field. In contrast, the mean directions from the northwestern Izu Peninsula show on average paleomagnetic directions are probably caused by tectonic deformations since 1.5 Ma. We propose a simple tilting model to explain these paleomagnetic directions.

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Intensity of the Earth's Magnetic Field in Geological Time

Abstract: Thellier

Cited by 36 publications

References 16 publications

Changes in earth’s dipole

Changes in earth’s dipole

Paleomagnetism and K-Ar Ages of Successive Lava Flows (4)

Paleomagnetism of Quaternary volcanics in the Izu peninsula and adjacent areas, Japan, and its tectonic significance.

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