Magnetotelluric soundings over the northeast Pacific may reveal spatial dependence of depth and conductance of the asthenosphere

Filloux, J. H.

doi:10.1016/0012-821x(80)90010-2

Cited by 82 publications

(46 citation statements)

References 8 publications

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“…Analyses of seafloor data obtained in the Pacific region showed a clear tendency of the depth to the asthenospheric conductor to increase with lithospheric age (FiLLoux, 1980;OLDENBURG, 1981), although more rigorous inversion of seafloor data somewhat weakens such a tendency (OLDENBURG et al, 1984). This tendency is consistent with models of plate growth (e.g.…”

Section: Introductionsupporting

confidence: 81%

“…The thickness of the oceanic lithosphere was inferred as follows. The depth to the conducting layer beneath the Pacific plate increases with the age of the plate (FILLOUX, 1980;YUKUTAKE et al, 1983) and is somewhat deeper than that to the low velocity layer (OLDENBURG, 1981). In the case of the Philippine Sea plate, the conducting layer has been supposed to exist at a depth of 30-50 km beneath the plate of 14-30 my (HONKURA, 1974(HONKURA, , 1983UTADA, 1987).…”

Section: Two-dimensional Modelingmentioning

confidence: 99%

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Electrical conductivity structure Beneath the Ryukyu trench-arc system and its relation to the subduction of the Philippine Sea plate.

Shimakawa¹,

Honkura

1991

J. geomagn. geoelec

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Seafloor measurements of geomagnetic variations were undertaken at six sites in the Ryukyu trench-arc system in order to investigate the electrical conductivity structure of the crust and upper mantle with special reference to the subduction of the Philippine Sea plate. In addition to the conventional analysis in which transfer functions for the vertical component are derived, we show the effectiveness of another type of transfer functions through which seafloor horizontal fields relate to horizontal fields simultaneously recorded on an island near seafloor sites. Because of the high attenuation of geomagnetic variations at periods shorter than 30 min at seafloor sites, analysis was possible only for the periods longer than 30 min. We estimated both types of transfer functions for the period range of 30 to 240 min. We attempted a two-dimensional modeling for a profile orthogonal to the strike of the Ryukyu trench-arc system, using a finite element method. The comparison of transfer functions derived from observations and calculations yields a model showing two columnar conductors in the mantle wedge; one at the depth range from 20 to 60 km in the forearc region and the other at the depth range from 60 to 130 km or more beneath the northwestern margin of the Okinawa Trough behind the arc. According to recent mineralogical studies, dehydration of some minerals in hydrated peridotite at depths of about 100 km and 150 km plays an important role on magma genesis in subduction zones. The columnar conductor found below the forearc region is likely to be a zone containing water released through dehydration of some minerals in the hydrated peridotite, whereas the columnar conductor beneath the northwestern margin of the Okinawa Trough seems to correspond to a zone of partial melting which may be triggered by water released through dehydration of some other minerals.

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Section: Introductionsupporting

confidence: 81%

Section: Two-dimensional Modelingmentioning

confidence: 99%

Electrical conductivity structure Beneath the Ryukyu trench-arc system and its relation to the subduction of the Philippine Sea plate.

Shimakawa¹,

Honkura

1991

J. geomagn. geoelec

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“…In this sense, a conclusion to be drawn from the present study would be that the thickness of about 60 my old plate ranges from 80 to 120 km in the West Philippine Basin area. In the northeastern Pacific, an asthenospheric conducting, layer exists at a depth of 85 km below the ocean floor of about 30 my age and at a depth of 135 km for the age of 72 my (FILLOUX, 1980). The above conclusion for the West Philippine Basin is in harmony with the results for the northeastern Pacific, although depth resolution is not quite high at present.…”

Section: Discussion and Concluding Remarkssupporting

confidence: 77%

“…melting zone in the asthenosphere, the existence of a conducting layer below 80-120 km as disclosed in the preceding section might imply that the thickness of the lithosphere is 100 km or so. On the other hand, the plate thickness is closely related with its age (e.g., YOSHII, 1975), and accordingly the depth to an asthenospheric conducting layer seems to depend on plate age (FILLOUX, 1980). In this sense, a conclusion to be drawn from the present study would be that the thickness of about 60 my old plate ranges from 80 to 120 km in the West Philippine Basin area.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 49%

Electrical conductivity structure beneath the northwestern philippine sea as inferred from the island effect on Minami-Daito Island.

Honkura

Isezaki

Yaskawa

1981

J. geomagn. geoelec

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Observations of short-period geomagnetic variations were carried out at three sites on Minami-daito Island in the northwestern Philippine Sea. The observed results clearly show the island effect; anomalous Z variations on the island, particularly characterized by a reversal of sign in Z variations between northern and southern stations for north-south magnetic fields. Response and current functions are determined from transfer function A obtained for the period range from 7 to 240 min.Numerical calculations of the island effect made on the basis of thin-sheet approximation can well account for the anomalous Z variations. Then, the response or current function obtained from the observed results is compared with those determined from the results of numerical calculations for underground conductivity models. It is concluded that a highly conducting layer exists at a likely depth range from 80 to 120 km beneath the northwestern Philippine Sea where Minami-daito Island is located. The conductivity of the layer is estimated as 0.5 S/m or so.

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“…Accordingly we undefined, which was to be determined by FEM. On the floor of the Pacific Ocean, magnetotelluric measurements have been conducted at several places (see FILLOUX, 1980;YUKUTAKE et al, 1983). All these measurements have indicated that a conducting layer exists at the depth of 100 km to 150km in the central and northwest Pacific and that resistivity of the because sediment cores taken from the ocean floor indicated the average conductivity of the sediment to be about 0.8S/m (see FILLOUX, 1967).…”

Section: Surface Resistivitiesmentioning

confidence: 99%

Two-dimensional modelling of resistivity structure beneath the Tohoku district, northern Honshu of Japan, by a finite element method.

Ogawa

Yukutake

Utada

1986

J. geomagn. geoelec

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Magnetotelluric soundings over the northeast Pacific may reveal spatial dependence of depth and conductance of the asthenosphere

Cited by 82 publications

References 8 publications

Electrical conductivity structure Beneath the Ryukyu trench-arc system and its relation to the subduction of the Philippine Sea plate.

Electrical conductivity structure Beneath the Ryukyu trench-arc system and its relation to the subduction of the Philippine Sea plate.

Electrical conductivity structure beneath the northwestern philippine sea as inferred from the island effect on Minami-Daito Island.

Two-dimensional modelling of resistivity structure beneath the Tohoku district, northern Honshu of Japan, by a finite element method.

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