Velocity structure and aftershock distribution of the 1982 Urakawa-Oki Earthquake.

Miyamachi, Hiroki; Moriya, Toshio

doi:10.4294/jpe1952.35.309

Cited by 12 publications

(8 citation statements)

References 12 publications

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“…They are plotted so that the length coincides with that of the reference when the axis is parallel to this vertical plane. The epicenter [ Suzuki and Motoya , 1983] and aftershock region [ Miyamachi and Moriya , 1987] of the 1982 Urakawa‐oki earthquake are shown projected by a star and thick gray lines, respectively. Geological interpretation is superimposed.…”

Section: Resultsmentioning

confidence: 99%

Delamination structure imaged in the source area of the 1982 Urakawa‐oki earthquake

Murai

Akiyama

Katsumata

et al. 2003

Geophysical Research Letters

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The Kuril arc collides with the northeast Japan arc in the southern part of Hokkaido, Japan. 3-D tomographic inversion of data from a dense network of sensitive ocean-bottom seismographs and land stations has allowed imaging of previously unseen details of the arc-arc collision structure. A low velocity body dips gently southwestward, at depths of 35 to 45 km, from east of the Hidaka Mountains to the source area of the 1982 Urakawa-oki destructive earthquake (Ms 6.8). The low velocity body is the lower half of the lower crust of the Kuril arc, which must have been delaminated by the collision. We believe that the continuing collision of the delaminated lower crust with the northeast Japan arc resulted as an episode of aseismic slow slip prior to the 1982 Urakawa-oki earthquake as well being the reason for the high seismic activity in this region

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Section: Resultsmentioning

confidence: 99%

Delamination structure imaged in the source area of the 1982 Urakawa‐oki earthquake

Murai

Akiyama

Katsumata

et al. 2003

Geophysical Research Letters

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“…Previous studies described the Hidaka mountains as a mid‐Miocene age north‐northwest trending belt that formed from the arc‐arc collision. Further work has investigated the complex velocity structure beneath the Hokkaido corner in terms of the crustal and upper mantle anomalies [ Miyamachi and Moriya , 1984; Moriya , 1986; Miyamachi and Moriya , 1987; Kimura , 1996; Moriya et al , 1998]. The timing of the collision in our model is consistent with the previous models, and has constrained the collision initiation with additional data confirming of the termination of volcanism in the Hidaka mountains [ Maeda , 1990; Maeda and Kagami , 1996].…”

Section: Discussionmentioning

confidence: 99%

Evolution of mantle structure beneath the northwest Pacific: Evidence from seismic tomography and paleogeographic reconstructions

Miller

2006

Tectonics

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Plate motions and subducting slab morphology are intricately connected, and through the integration of seismicity, tomographic images, and relative plate motions, the evolution of mantle structure can be interpreted. Tomographic images of P wave, shear wave speed, and bulk sound speed perturbations of the northwest Pacific region have been interpreted to define the extent and geometry of the subducting Pacific plate. We have found that the subducted Pacific plate beneath the Japan and Kurile arcs is coherent but is very complex at the junction of the two arcs near the Hokkaido corner, as the slab subduction angle decreases from north to south while the slab thickens. The Pacific slab beneath the Japan arc is slightly thinner and subducting through the upper mantle at a less steep angle than the slab beneath the Kurile arc. As the slab reaches the 660‐km discontinuity it becomes stagnant and lies in a horizontal position on top of the transition zone both beneath the Izu and Japan arcs. In contrast, the slab beneath the Kurile arc is subducting at a steeper angle and penetrates through the transition zone into the lower mantle. The difference in slab morphology appears to be due to a combination of change in dip of the subducting plate and the convergence velocity of the Pacific plate along the margin. A new paleogeographic reconstruction of northeast Asia was assembled to evaluate the plate motions that could explain the foundation of the current slab morphology. The plate reconstruction was based on Euler pole motions of the Pacific, Philippine, Amurian, Okhotsk, and North American plates relative to stable Eurasia plate. The new tectonic model illustrates the collision of the Japan and Kurile arcs, the opening of the Kurile Basin, disparity in Pacific plate velocities along the arc, and different rates of trench retreat along the Izu, Japan, and Kurile segments of the western Pacific margin. The plate motion model was interpreted in conjunction with the physical properties of the mantle imaged with the P wave and joint tomography to assess the evolution of the Pacific plate morphology since the mid‐Miocene and to provide constraints on the plausible plate motions in the region.

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“…They also found that seismicity is very active in the low velocity zone. 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.…”

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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Velocity structure and aftershock distribution of the 1982 Urakawa-Oki Earthquake.

Cited by 12 publications

References 12 publications

Delamination structure imaged in the source area of the 1982 Urakawa‐oki earthquake

Delamination structure imaged in the source area of the 1982 Urakawa‐oki earthquake

Evolution of mantle structure beneath the northwest Pacific: Evidence from seismic tomography and paleogeographic reconstructions

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

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