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

NAKANISHI, Ichiro

doi:10.4294/jpe1952.33.241

Cited by 28 publications

(18 citation statements)

References 13 publications

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“…Miyamachi and Moriya (1987) revealed a complex P wave velocity distribution down to a depth of 20 km in and around the aftershock region of the 1982 Urakawa-Oki Earthquake using the inverse method of Thurber (1983). Nakanishi (1985) applied a tomographic inverse method based on the Algebraic Reconstruction Technique of Herman (1980) to the Hokkaido-Tohoku region and obtained a P wave high velocity zone down to a depth of 120 km. However, these previous studies could not explicitly reveal the depth distributions of the Conrad, Moho and plate boundaries beneath the Hokkaido region.…”

Section: Introductionmentioning

confidence: 99%

Seismic Velocity Structure in the Crust and Upper Mantle beneath Northern Japan.

et al. 1994

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W e have applied an inverse method to P and S wave arrival time data observed at 52 seismic stations for 349 local earthquakes in order to estimate a three-dimensional (3-D) velocity structure beneath northern Japan. The method is characterized by a simultaneous determination of the two-dimensional depth distributions of velocity boundaries, 3-D velocity distribution and station corrections as well as hypocenter parameters of earthquakes. The Moho discontinuity under eastern Hokkaido is inclined from a depth of 32 km beneath the Hidaka Mountains to 20 km beneath the Konsen Plateau, while the thick crust with a thickness of 30-36 km distributes widely in western Hokkaido and the Tohoku region. The dip direction of the Moho in eastern Hokkaido is approximately perpendicular to the range of the Hidaka Mountains. The upper boundary of the subducting Pacific plate distributes in the depth range from 50 to 170 km in the surveyed area and the dip angle of the plate boundary in eastern Hokkaido (the Kurile arc) is slightly larger than that in the Tohoku region (the northeastern Japan arc).Estimated P (S) wave velocities are 5.8-7.0 km/s (3.4-4.1 km/s) in the crust, 7.4-8.0 km/s (4.2-4.5 km/s) in the upper mantle, and 8.1-8.6 km/s (4.6-4.9 km/s) in the plate, respectively. The velocities in the crust beneath northern Hokkaido are lower than those beneath eastern Hokkaido and the Tohoku region. The upper mantle has velocities which gradually increase with depth, and the subducted plate contains a high velocity zone with a P wave velocity faster than 8.3 km/s. VP/VS ratios derived from P and S wave velocities generally range from 1.75 to 1.80 in the crust and upper mantle, while the ratios in the high velocity zone within the plate are less than 1.75. These results suggest that the plate is composed of two layers: the first layer is a low-velocity and high-VP/VS zone with a thickness less than 20 km, and the second layer is a thick high-velocity and low VP/VS zone. The estimated plate thickness is about 90 km in the Kurile arc and about 110 km in the northeastern Japan arc.The relocated hypocenter distribution beneath Hokkaido clearly shows the double seismic plane in the subducting plate. The upper seismic plane is located in the first Received April 27, 1994; Accepted October 5, 1994 * To whom correspondence should be addressed . ** Present address: Faculty of Science , Kyushu University, Fukuoka 812, Japan. layer with a low velocity and the lower seismic plane is in the second layer with a high velocity. The seismic activity in the upper seismic plane is high in the depth range from 60 to 90 km, while that in the lower seismic plane is high at depths deeper than 100 km. The double seismic plane joins at depths from 90 to 130 km.

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Section: Introductionmentioning

confidence: 99%

Seismic Velocity Structure in the Crust and Upper Mantle beneath Northern Japan.

et al. 1994

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“…Miyamachi and Moriya, 1984;Nakanishi, 1985;Hasemi et al, 1984;Obara et al, 1986;Sato et al, 1989;Zhao, 1991;Zhao et al, 1992;Zhao and Hasegawa, 1993). The methods for modeling the 3-D velocity structure used in these studies are basically classified into two: one is a discrete method represented by the "block configuration" of Aki and Lee (1976) or the "grid configuration" of Thurber (1983), and the other is the functional method using some continuous functions (Horiuchi et al, 1982;Ashiya et al, 1987).…”

Section: Introductionmentioning

confidence: 99%

A Method for Determination of the Three-Dimensional Seismic Velocity Structure from Local Earthquake Data.

Miyamachi

1994

J,Phys,Earth

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We have developed an inverse method to estimate a three-dimensional seismic wave velocity structure using seismic arrival time data obtained from local earthquakes. The method is characterized by a simultaneous determination of a two-dimensional depth distribution of a velocity boundary, a three-dimensional velocity distribution, station corrections and hypocenters. The depth distributions of velocity boundaries and the distributions of the slowness perturbations for P and S waves are modeled by power series of latitude, longitude, and depth, This representation of the three-dimensional seismic structure is advantageous not only in reducing the number of unknown parameters, but also in analytically evaluating the boundary depths, velocities, and partial derivatives of travel times with respect to the unknown parameters. Ray trajectories connected between hypocenters and stations are determined by the so-called shooting method for ray tracing scheme under a simplified velocity distribution with the exact boundary depth distribution. Numerical experiments have proved that our inverse method can successfully estimate the three-dimensional velocity structure.

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“…Because of the danger of structural signal being mapped into biased hypocentral parameters, large mislocations may have a significant effect on investigations where both the locations and travel times of seismic waves from deep earthquakes are used. Examples include studies of the physical mechanism of deep-focus earthquakes (Iidaka andSuetsugu, 1990, 1992;Helffrich and Brodholt, 1991), investigations of subduction zone morphology with seismic imaging techniques such as bodywave tomography (for northwest Pacific slab structure: Hirahara and Mikumo, 1980;Nakanishi, 1985;Kamiya et al, 1988;Suetsugu, 1989;Spakman et al, 1989;Zhou and Clayton, 1990; The reflection points of pP add, in effect, local sources and receivers (Engdahl and Billington, 1986;Engdahl and Gubbins, 1987). 1992; Fukao et al, 1992) and residual sphere analyses (e.g.…”

Section: Introductionmentioning

confidence: 99%

Step-wise relocation of ISC earthquake hypocenters for linearized tomographic imaging of slab structure

Hilst

Engdahl²

1992

Physics of the Earth and Planetary Interiors

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Van der Hi 1st, R.D. and Engdahl, E.R., 1992.Step-wise relocation of ISC earthquake hypocenters for linearized tomographic imaging of slab structure. Phys. Earth Planet. Inter., 75: 39-53.A vast volume of seismic phase data, computed from routinely determined hypocenter locations, is presently available for seismic imaging techniques such as tomographic inversion and residual sphere analysis. Routinely reported earthquake hypocenters, however, can be in error by several tens of kilometers. These biases in hypocenter location can result in the misidentification of seismic phases and the loss of structural signal in the seismic phase data. Thus, the value of these data in constraining seismic images is significantly reduced. Furthermore, hypocenter mislocations degrade the linearization of the tomographic problem and map into the images produced by tomographic inversion.To obtain adequate reference hypocenters for linearized inversion, we used iasp91 software and reported arrival times to reprocess ISC hypocenters and phase data for northwest Pacific earthquakes. Subsequently, we inverted P-and pP-wave residuals for Earth structure and source (mis)location. We describe this step-wise relocation of ISC hypocenters, which underlies the linearization of the tomographic inversion, and compare the relocation vectors before and after inversion.The hypocenter relocations determined prior to inversion are of the order of 10 km, which is significant with regard to both the estimated standard errors and the effect on travel-time residuals, and systematic with regard to earthquake position in the subducted slab. In contrast, the spatial components of the relocation vectors determined upon inversion of P and pP residuals are up to an order of magnitude smaller, do not reveal a correlation with location in the seismic zone, and do not generally exceed the noise level.The incorporation of pP data in the relocation was essential to remove the depth bias prior to inversion, to retrieve slab signal that might have been absorbed in mislocation, and to constrain the focal depth upon seismic inversion. Non-linear inversion schemes will not be efficient in removing the depth bias or in retrieving lost slab signal unless seismic phases that contain additional information about the depth bias, like the depth phase pP, are used.

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

Cited by 28 publications

References 13 publications

Seismic Velocity Structure in the Crust and Upper Mantle beneath Northern Japan.

Seismic Velocity Structure in the Crust and Upper Mantle beneath Northern Japan.

A Method for Determination of the Three-Dimensional Seismic Velocity Structure from Local Earthquake Data.

Step-wise relocation of ISC earthquake hypocenters for linearized tomographic imaging of slab structure

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