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

Ogawa, Yasuo; Yukutake, Takesi; Utada, Hisashi

doi:10.5636/jgg.38.45

Cited by 31 publications

(34 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The resistivity of the conductive lower crust is lower in the western half of the survey area than that of the eastern one. Low resistivity in the lower crust to the west of the volcanic front has been proposed formerly by OGAWA et al (1986) in almost the same region. Their modeling was based on geomagnetic depth sounding technique in the period range from 15 min to 60 min.…”

Section: Discussionmentioning

confidence: 90%

“…From the anisotropic effect of impedance, especially the phase of the impedance, western margin of this conductor in the lower crust has been reconfirmed. The most conductive body (10 ohm-m) in the lower crust extending from site 20 to site 40 seems to have relation to the Quaternary volcanoes as discussed by OGAWA et al (1986).…”

Section: Discussionmentioning

confidence: 99%

“…In the Tohoku district, many deep geoelectrical surveys have been carried out and resistivity models have been proposed by many authors (KATO et al, 1971;HONKURA, 1974;SATO, 1981; RESEARCH GROUP FOR CRUSTAL RESISTIVITY STRUCTURE, JAPAN, 1983;OGAWA et al,1986). KATO et al (1971) proposed a model of the resistivity structure from the analysis of the geomagnetic variations for the period range of geomagnetic pulsations.…”

Section: Introductionmentioning

confidence: 99%

“…OGAWA et al (1986) analyzed these transfer functions combining transfer functions from the ocean bottom measurements in the Pacific ocean (YUKUTAKE et al,1983). They concluded, from the frequency and spatial dependence of eastward component of the geomagnetic transfer functions, that the lower crust is very conductive (5 ohm-m) beneath the volcanic region between the Japan Sea coast and the volcanic front.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Two-dimensional resistivity modeling based on regional magnetotelluric survey in the northern Tohoku district, northeastern Japan.

Ogawa

1987

J. geomagn. geoelec

Self Cite

View full text Add to dashboard Cite

In 1984, a regional Magnetotelluric (MT) survey was carried out in the northern Tohoku district in the frequency range from 17.4 kHz to 1/256 Hz. MT stations wereThe shallow lateral inhomogeneity was evaluated from ELF-MT (8 to 20 Hz) and VLF-MT (17.4 kHz) survey at 35 sites, and the deep structure was investigated using ULF-MT (1/4 to 1/256 Hz) survey at 7 sites.Two-dimensional modelings with north-south strike are carried out. Analyses are done with special reference to the anisotropic behavior of phase of impedance. From the modeling with north-south strike, the following features are found. (1) For TM mode, where electric field is directed eastward, frequency characteristics and spatial dependence of impedance are primarily due to effect of oceans and shallow resistivity distribution. For 1/16 Hz, coastal effect alone cannot account for the observed impedance and conductor (300 ohm-m) is required beneath the eastern part of the profile whose top is located at 10 km depth in the crust. (2) On the other hand, for TE mode, where electric field is directed northward, the spatial and frequency dependence of impedance requires the existence of a conductor (10 ohm-m) in lower crust beneath the volcanic region whose depth ranges from 20 km to 30 km. This conductor is in harmony with low seismicity, low velocity, and shallow Curie isotherm depth.

show abstract

Section: Discussionmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Two-dimensional resistivity modeling based on regional magnetotelluric survey in the northern Tohoku district, northeastern Japan.

Ogawa

1987

J. geomagn. geoelec

Self Cite

View full text Add to dashboard Cite

show abstract

“…Observation of geomagnetic variations has been carried out from time to time on the Japanese Islands and various models of the conductivity structure in the upper mantle have been proposed (RIKITAKE, 1969;HONKURA, 1974;OGAWA et al, 1986), but determination of the conductivity structure covering the entire trench-arc system was incomplete without the observation at seafloor. The development of seafloor instruments (SEGAWA et al, 1982(SEGAWA et al, , 1983) eliminated the technical difficulties and seafloor observations have been undertaken very actively since 1981 (e.g.…”

Section: Introductionmentioning

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

View full text Add to dashboard Cite

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.

show abstract

Time causal operational estimation of electric fields induced in the Earth's lithosphere during magnetic storms

Love

Swidinsky

2014

Geophys. Res. Lett.

View full text Add to dashboard Cite

In support of projects for monitoring geomagnetic hazards for electric power grids, we develop a simple mathematical formalism, consistent with the time causality of deterministic physics, for estimating electric fields that are induced in the Earth's lithosphere during magnetic storms. For an idealized model of the lithosphere, an infinite half‐space having uniform electrical conductivity properties described by a galvanic tensor, we work in the Laplace‐transformed frequency domain to obtain a transfer function which, when convolved with measured magnetic field time series, gives an estimated electric field time series. Using data collected at the Kakioka, Japan observatory, we optimize lithospheric conductivity parameters by minimizing the discrepancy between model‐estimated electric field variation and that actually measured. With our simple model, we can estimate 87% of the variance in storm time Kakioka electric field data; a more complicated model of lithospheric conductivity would be required to estimate the remaining 13% of the variance. We discuss how our estimation formalism might be implemented for geographically coordinated real‐time monitoring of geoelectric fields.

show abstract

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

Cited by 31 publications

References 27 publications

Two-dimensional resistivity modeling based on regional magnetotelluric survey in the northern Tohoku district, northeastern Japan.

Two-dimensional resistivity modeling based on regional magnetotelluric survey in the northern Tohoku district, northeastern Japan.

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

Time causal operational estimation of electric fields induced in the Earth's lithosphere during magnetic storms

Contact Info

Product

Resources

About