Fine structure beneath the Tohoku district, northeastern Japan arc, as derived by an inversion of P-wave arrival times from local earthquakes

Hasemi, Akiko; Ishii, Hiroshi; Takagi, Akio

doi:10.1016/0040-1951(84)90116-1

Cited by 65 publications

(35 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The proposed model is also in good agreement with the thermal structure inferred from Curie point isotherm depth (NEDO,1982;Tsu and OGAWA, 1982), with the low seismicity in the lower crust or with low velocity anomaly in the crust (HASEMI et al, 1984;OBARA et al, 1986).…”

Section: Resultssupporting

confidence: 74%

“…Recently, intensive studies on crustal and upper mantle inhomogeneities in the Tohoku district have been carried out by analyzing P-wave (HASEMI et al,1984) and P-, S-wave velocity structures (OBARA et al, 1986). In their results, most anomalous parts of the P-and S-wave velocity are located in the crust beneath the active volcanic regions, although vertical resolution is 30 km.…”

Section: Discussionmentioning

confidence: 99%

“…In their results, most anomalous parts of the P-and S-wave velocity are located in the crust beneath the active volcanic regions, although vertical resolution is 30 km. HASEMI et al (1984) suspected that this low velocity may have something to do with the magma segregation. The distribution of the low velocity anomaly is in good harmony with that of the conductive body (10 ohm-m) in the lower crust.…”

Section: Discussionmentioning

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

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: Resultssupporting

confidence: 74%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

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

Ogawa

1987

J. geomagn. geoelec

View full text Add to dashboard Cite

show abstract

“…From observations by the seismic network station, HASEMI et al (1984) examined the three-dimensional distribution of P wave velocity, -dV/V in the Tohoku district (see Fig. 16).…”

Section: Discussionmentioning

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

View full text Add to dashboard Cite

“…1 for the locations). These low velocities were also derived by HASEMI et al (1984) from a damped least-squares inversion of P-arrival times obtained by the local seismic network of Tohoku University. In the Hokkaido region the velocities of layer 1 are relatively high compared with the reference model except an area near stations URA and OBI (Fig.…”

Section: Average 3-d Model For 1973-1981mentioning

confidence: 99%

Three-dimensional structure beneath the Hokkaido-Tohoku region as derived from a tomographic inversion of P-arrival times.

NAKANISHI

1985

J,Phys,Earth

View full text Add to dashboard Cite

An approximate inversion method, which has been widely used in medical science and called ART (Algebraic Reconstruction Technique), is applied to obtain a 3-D image of the uppermost mantle beneath the Hokkaido-Tohoku region for the period from 1973 to 1981. About 7,600 P-wave arrival times recorded by seismic stations of the Japan Meteorological Agency are used. We present three types of 3-D models. 1) A model from the 7,600 data. 2) Models for 1973-1977 and 1978-1981, respectively. 3) Eight models for 2 years moving windowed data. The first model is in good accordance with the results of previous authors who inverted P-arrival time data by damped leastsquares inversion methods. The model clearly exhibits a high-low velocity contrast along the strike of the deep-seismic zone below a depth of about 60 km. The contrast is estimated to be about 4%. A subtraction operation of the second type 3-D models does not seem to show any significant differences between the models. No significant variations are apparent in and around the source region of the 1982 Urakawa-oki earthquake (MS=7.2) in the display of the 2 years windowed results. However, the latter two results do not necessarily deny possible velocity change if we consider the sensitivity of event location process to the expected velocity change in the source area of earthquake.

show abstract

Fine structure beneath the Tohoku district, northeastern Japan arc, as derived by an inversion of P-wave arrival times from local earthquakes

Cited by 65 publications

References 23 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.

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

Three-dimensional structure beneath the Hokkaido-Tohoku region as derived from a tomographic inversion of P-arrival times.

Contact Info

Product

Resources

About