Structure of the Japan Trench subduction zone, from multi-channel seismic-reflection records

Matsuzawa, Akira; Tamano, Toshiro; Aoki, Yasuhiro; Ikawa, Takeshi

doi:10.1016/0025-3227(80)90029-8

Cited by 16 publications

(6 citation statements)

References 3 publications

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“…Also, seismic reflection profiles depict at least two reflectors that can be traced across the trench; these reflectors are horizons marking the subducting ocean crust. The interval velpcity between the two reflectors, the latter interpreted as the Moho boundary, is estimated to be about 6.5 km/s, from which the Layer 2 subduction cannot be substantiated (Matsuzawa et al, 1980). Murauchi and Ludwig (1980) compiled the available seismic data and produced a vertical section across the Japan Trench.…”

Section: Previous Resultsmentioning

confidence: 99%

“…P7, P8, P9, and P12 are two-ship refractions (Ludwig et al, 1966;Murauchi and Ludwig, 1980). JNOC 1, JNOC 2 and ORI 78-3, ORI 78-4 are multichannel reflection lines (Matsuzawa et al, 1980;Nasu et al, 1980;Tamano et al, 1981). Jl, J2, and J12 are sonobuoy measurements and OBS refractions (Nagumo et al, 1980;Murauchi and Ludwig, 1980).…”

Section: Results Of the 1982 Experimentsmentioning

confidence: 99%

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Air Gun-Ocean Bottom Seismograph Seismic Structure across the Japan Trench Area

Suyehiro¹,

Kanazawa²,

Shimamura³

1986

Initial Reports of the Deep Sea Drilling Project

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A number of controlled-source seismic refraction studies using an ocean bottom seismograph (OBS) array have been made in the Japan Trench area recently. This report focuses on results from airgun data of two experiments. The first carried out in 1981, had a 250 km-long profile along the 3000-m depth contour on the landward side of the trench. The second experiment, conducted in 1982, had a 300-km-long profile along the inner lower trench slope and also included two profiles perpendicular to the trench axis. General features previously discovered were more firmly established by the nature of bottom measurements and the close spacing of the shots. Continental-type upper crust exists as near as 40 km landward of the trench, and a thick sedimentary, low-velocity prism underlies the inner lower trench slope. The depths of the subducting Moho boundary are a few kilometers shallower than previously thought and dip more gently from beneath the trench axis to the continental slope break. It is difficult to substantiate Layer 2 subduction because of its thickness and probable gradual transition to Layer 3.

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Section: Previous Resultsmentioning

confidence: 99%

Section: Results Of the 1982 Experimentsmentioning

confidence: 99%

Air Gun-Ocean Bottom Seismograph Seismic Structure across the Japan Trench Area

Suyehiro¹,

Kanazawa²,

Shimamura³

1986

Initial Reports of the Deep Sea Drilling Project

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“…Instead the uppermost part Figure 12. JNOC multichannel seismic record, Crossline C (after Matsuzawa et al, 1980). Line crosses just south of Site 441 (see Figure 3).…”

Section: Seismic Reflectionmentioning

confidence: 99%

Site 441, Japan Trench Lower Slope, Leg 57

Huene¹,

Keller²,

Arthur³

et al. 1980

Initial Reports of the Deep Sea Drilling Project

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“…Topographical features of the subduction zone, such as trenches, island arcs and marginal seas, are shown. of seismic refraction and reflection experiments were carried out and outlined the transition from oceanic t o the continental structure (Ludwig et al 1966;Murauchi & Ludwig 1980;Nagumo, Kasahara & Koresawa 1980;Nasu et al 1980;Matsuzawa et al 1980;Tamano, Toba & Aoki 1981 ;Suyehiro et al 1985;Suyehiro, Kanazawa & Shimamura 1986). General features of the Japan Trench show a continental type upper crust as near as 40 km landward of the trench, a thick sedimentary low wavespeed prism beneath the lower inner trench slope and normal oceanic type crust seaward of the trench.…”

Section: Introductionmentioning

confidence: 99%

Crustal structure across the Kurile Trench off south-eastern Hokkaido by airgun-OBS profiling

Nishizawa

Suyehiro

1986

Geophysical Journal International

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Seismic refraction profiles were shot across the Kurile Trench, south-east of Hokkaido, Japan. The experiment in a typical island arc-trench system, where the Pacific Plate subducts beneath Hokkaido, was designed to investigate the transition of crustal structure from oceanic basin to continental slope across the trench. High resolution data were obtained from a 9 litre airgun and multi-OBS system. They were processed through a series of operations: digitization, filtering, slant stacking, 7-sum inversion, twodimensional ray tracing, and comparison with synthetic seismograms.A typical oceanic structure composed of an unconsolidated sedimentary layer (P wavespeed of 1.8-2.2 kms-' , thickness of 0.5-1 km), layer 2 (3.1-5.8 kms-' , 1-2 km) with a large wavespeed gradient, and relatively homogeneous layer 3 (6.0-6.8 km s-* , 5 km) is found on the oceanic side of the trench. Observations of shear waves converted at the boundary between the sedimentary layer and layer 2 gave compressional to shear wavespeed ratios of about 7.0 for the topmost sedimentary layer and 1.73--1.77 for layers 2 and 3. The transition of structure occurs slightly landward of the trench axis and thick low wavespeed materials (P wavespeed of 2.5-4.7 km s-l) persist beneath the continental slope. The density profile derived from our wavespeed structure is consistent with published free-air gravity anomaly data.The general crustal structure in the southern part of the Kurile Trench is similar to that of the Japan Trench off Sanriku. However, the distribution of the thick low wavespeed materials on the continent side differs between the two trench regions. These materials are more abundant in the Kurile Trench region, as is also inferred from the gravity anomaly pattern. The variability of the gravity anomaly on the continental side along the trench axis suggests that the distribution of these materials changes even within a single trench system. 372 A. Nishizawa and K. SuyehiroThe seismic activity inferred from S-P time distribution at each OBS is high near the trench, and low in the oceanic basin beyond about 30 km from the trench axis as well as on the continental side where thick low wavespeed materials exist. An activity which seems to occur exactly in the narrow transition zone dividing the typical oceanic crust and the thick low wavespeed materials in the continental side structure is found.

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Structure of the Japan Trench subduction zone, from multi-channel seismic-reflection records

Cited by 16 publications

References 3 publications

Air Gun-Ocean Bottom Seismograph Seismic Structure across the Japan Trench Area

Air Gun-Ocean Bottom Seismograph Seismic Structure across the Japan Trench Area

Site 441, Japan Trench Lower Slope, Leg 57

Crustal structure across the Kurile Trench off south-eastern Hokkaido by airgun-OBS profiling

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