Velocity Structure Beneath the Hidaka Mountains in Hokkaido, Japan

Miyamachi, Hiroki; Moriya, Toshio

doi:10.4294/jpe1952.32.13

J,Phys,Earth

1984

DOI: 10.4294/jpe1952.32.13

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Velocity Structure Beneath the Hidaka Mountains in Hokkaido, Japan

Hiroki Miyamachi

Toshio Moriya

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Cited by 48 publications

(54 citation statements)

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“…Relation between P-wave Velocity Structure and the Urakawa-oki Earthquake P-wave velocity structure beneath Hidaka mountains and off Urakawa region have been studied by ASANO et al (1979), DEN and HOTTA (1973), FUJII and MORIYA (1983), MORIYA (1984), andTAKANAMI (1982). DEN and HOTTA (1973) and ASANO et al (1979) found a thick sedimentary layer of 10-17 km with a velocity of 4.2 km/s beneath the continental slope off Urakawa by refraction and reflection experiments.…”

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confidence: 99%

“…2, containing the deep seismic zone, on which boundaries of the low velocity zone presented by MIYAMACHI and MORIYA (1984) are also shown. MIYAMACHI and MORIYA (1984) inferred that the material in the low velocity zone originates from the crust and that the inclined low velocity zone is the subducted crust resulting from collision between the Kurile and the northern Honshu arcs. The boundaries can be traced down to a depth of 80 km.…”

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confidence: 99%

“…A pair of arrows denotes the fault motion of the mainshock. The inserted figure shows studied area and measurement lines used to compile the structure: A, the aftershock area by MORIYA et al (1983); B , the area in the square studied by MIYAMACHI and MORIYA (1984) using three-dimensional inversion method and observation area of the quarry blasts by FUJII and MORIYA (1983); D , refraction and reflection measurement lines after DEN and HOTTA (1973) and ASANO et al (1979). Focal mechanism solution in the inserted figure (equal area projection of the lower hemisphere) after MORIYA et al (1983) is modified to reader's side hemisphere projection in the main figure.…”

mentioning

confidence: 99%

“…FUJII and MORIYA (1983), through travel-time analysis of the refracted waves from the quarry blasts in the central part of Hidaka mountains, found that sedimentary layers of 3.6 km/s and 4.7 km/s become thick stepwise along the west side of Hidaka mountains reaching a depth of 9 km beneath the coastal region of Hidaka. TAKANAMI (1982) and MIYAMACHI and MORIYA (1984) using the P-wave arrival-time data of local earthquakes, obtained threedimensional structures beneath Hidaka mountains where strong lateral heterogeneity exists. MIYAMACHI and MORIYA (1984) proposed a model in which an inclined low velocity zone exists and Pacific plate is confined below the low velocity zone.…”

mentioning

confidence: 99%

“…TAKANAMI (1982) and MIYAMACHI and MORIYA (1984) using the P-wave arrival-time data of local earthquakes, obtained threedimensional structures beneath Hidaka mountains where strong lateral heterogeneity exists. MIYAMACHI and MORIYA (1984) proposed a model in which an inclined low velocity zone exists and Pacific plate is confined below the low velocity zone. These results show that the structure of the region considered is complicated; that is, the average P-wave velocities of the crust and upper mantle are extremely low compared with those in other regions in Japan (e.g., AOKI et al, 1972;OKADA et al, 1973;SASAKI et al, 1970;YOSHII and ASANO, 1972;YOSHII et al, 1974).…”

mentioning

confidence: 99%

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Collision of Forearcs and Overlapped Deep Seismic Zone in the Transitional Zone Between the Northern Honshu and Kurile Arcs

Moriya

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mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Collision of Forearcs and Overlapped Deep Seismic Zone in the Transitional Zone Between the Northern Honshu and Kurile Arcs

Moriya

1986

J,Phys,Earth

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Detailed seismic attenuation structure beneath Hokkaido, northeastern Japan: Arc‐arc collision process, arc magmatism, and seismotectonics

et al. 2014

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In this study, we imaged a detailed seismic attenuation structure (frequency-independent Q À1 ) beneath Hokkaido, Japan, by merging waveform data from a dense permanent seismic network with those from a very dense temporary network. Corner frequency of each event used for t* estimation was determined by the S coda wave spectral ratio method. The seismic attenuation (Q p À1 ) structure is clearly imaged at depths down to about 120 km. For the fore-arc side of Hokkaido, high-Q p zones are imaged at depths of 10 to 80 km in the crust and mantle wedge above the Pacific slab. Low-Q p zones are clearly imaged in the mantle wedge beneath the back-arc areas of eastern and southern Hokkaido. These low-Q p zones, extending from deeper regions, extend to the Moho beneath volcanoes, the locations of which are consistent with those of seismic low-velocity regions. These results suggest that the mantle wedge upwelling flow occurs beneath Hokkaido, except in the area where there is a gap in the volcano chain. In contrast, an inhomogeneous seismic attenuation structure is clearly imaged beneath the Hokkaido corner. A broad low-Q p zone is located at depths of 0-60 km to the west of the Hidaka main thrust. The location almost corresponds to that of the seismic low-velocity zone in the collision zone. The fault planes of the 1970 M6.7 and 1982 M7.1 earthquakes are located at the edges of this broad low-Q p zone. Observations in this study indicate that our findings contribute to understanding the detailed arc-arc collision process, magmatism, and seismotectonics beneath Hokkaido.

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Anisotropic tomography of Hokkaido reveals delamination‐induced flow above a subducting slab

et al. 2015

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We present a new 3-D anisotropic seismic model for the crust and upper mantle beneath Hokkaido (Japan) based on tomographic inversion of P and S arrival times from a regional seismic database. The P model is parameterized with three parameters at each point that describe the azimuthal anisotropy; the S model is represented isotropically. The isotropic P and S velocity anomalies match nearly perfectly. In the crust, they show a prominent linear anomaly in central Hokkaido along the Kamuikotan and Hidaka Belts, which represents the area of eastward underthrusting of the Japan Block underneath the Kuril fore arc. We interpret the high-velocity anomaly beneath the Hidaka zone as being delaminated mafic crust and entrained mantle lithosphere, which developed due to crustal shortening in the collision zone. One of our vertical sections shows a very unusual configuration for a subduction zone: a low-velocity slab is overlain by a high-velocity body in the mantle wedge. We propose that the high-velocity delaminated material sinking along the slab surface prevents the escape of fluids and melts from the upper part of the slab, where they are generated due to phase transitions. As a result, a large portion of the fluids is entrained downward and lowers the seismic velocities in the slab. The azimuthal anisotropy in the crust clearly corresponds to the major tectonic units and delineates the major suture zones. In the mantle, the anisotropy has a fan-shaped configuration and most likely represents the deviating of flows starting in southern Hokkaido and splitting into three directions. The western and eastern flows proceed toward the two volcanic groups on Hokkaido, and they may carry with them additional material to trigger the characteristic caldera-forming eruptions in these groups.

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Velocity Structure Beneath the Hidaka Mountains in Hokkaido, Japan

Cited by 48 publications

References 24 publications

Collision of Forearcs and Overlapped Deep Seismic Zone in the Transitional Zone Between the Northern Honshu and Kurile Arcs

Collision of Forearcs and Overlapped Deep Seismic Zone in the Transitional Zone Between the Northern Honshu and Kurile Arcs

Detailed seismic attenuation structure beneath Hokkaido, northeastern Japan: Arc‐arc collision process, arc magmatism, and seismotectonics

Anisotropic tomography of Hokkaido reveals delamination‐induced flow above a subducting slab

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