Sediments and structure of the Japan Trench

Ludwig, W. J.; Ewing, John; Ewing, Maurice; Murauchi, Sadanori; Den, Nozomu; Asano, Shûzô; Hara, Hiroshi; Hayakawa, M.; Asanuma, T.; Ichikawa, Kanenori; Noguchi, Iwao

doi:10.1029/jz071i008p02121

Cited by 247 publications

(76 citation statements)

References 15 publications

(2 reference statements)

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“…This thinning of the crust has been cited by Worzel (1965) as evidence of extensional forces on the seaward side of island arc trenches. The same effect is shown by Ludwig et al (1966) for the Japan Trench. Isaacs et al (1968) show that extensional stresses are predicted on the convex side of the bend of the downmoving lithosphere beneath island arcs, even though the principal stress, deeper in the lithosphere, may be compressional.…”

Section: Setting and Purposesupporting

confidence: 66%

Site 28

Bader¹,

Gerrard²,

Bronson³

et al. 1970

Initial Reports of the Deep Sea Drilling Project

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The Shipboard Scientific Party 1 SETTING AND PURPOSEThe Outer Ridge, which lies between the north wall of the Puerto Rican Trench and the Nares Basin to the north, is covered for the most part with thick, acoustically "transparent" sediments, diminishing in thickness northward where they dip beneath turbidites of the Nares Abyssal Plain (Ewing and Ewing, 1962; Ewing etal, 1965).Along the southern portion of the Outer Ridge, reflection profiles reveal that the basement layer reaches a maximum elevation, while the sediment cover diminishes to less than 0.2 second acoustical thickness near the north wall of the Puerto Rican Trench. Seismic refraction measurements show that the Outer Ridge crustal layers are unusually thin and that the 8.2 km/sec mantle reaches within less than 5 kilometers of the ocean bottom in this area. This thinning of the crust has been cited by Worzel (1965) as evidence of extensional forces on the seaward side of island arc trenches. The same effect is shown by Ludwig et al. (1966) for the Japan Trench. Isaacs et al. (1968) show that extensional stresses are predicted on the convex side of the bend of the downmoving lithosphere beneath island arcs, even though the principal stress, deeper in the lithosphere, may be compressional. Hersey (1966) described the typical Outer Ridge sedimentary section (from seismic refraction and reflection measurements) as having an upper zone of unconsolidated, acoustically "transparent" sediments separated from basement rock by a semi-transparent layer having a considerably higher compressional wave velocity (4.2 km/sec), assumed to be layered rock or sediment. Figure 1 shows the topography of the Outer Ridge, the position of Site 28, and the location of a reflection profiler transect which is presented in Figure 2. Figure 3, from Ewing and Ewing (1962), shows a section drawn

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Section: Setting and Purposesupporting

confidence: 66%

Site 28

Bader¹,

Gerrard²,

Bronson³

et al. 1970

Initial Reports of the Deep Sea Drilling Project

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“…This is seen particularly well in single-channel seismic records ( Figure 32; Ludwig et al, 1966;Tamaki et al's [1977] fig. 10).…”

Section: Sediment Transport and Depositional Features In Geophysical mentioning

confidence: 81%

Sedimentary Evolution of the Japan Fore-Arc Region off Northern Honshu, Legs 56 and 57, Deep Sea Drilling Project

Arthur¹,

Huen²,

Adelseck³

1980

Initial Reports of the Deep Sea Drilling Project

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The evolution of Neogene and Quaternary sedimentation in the fore-arc region off northern Honshu is evaluated using multichannel and single-channel seismic records in conjunction with the drill holes of the Japan Trench Transect (DSDP/IPOD Legs 56-57). The outer forearc region, which consisted of older sedimentary rocks and some calc-alkaline volcanic rocks, was subaerially exposed and eroded during the Paleogene and part of the Neogene. The deep sea terrace (fore-arc basin) region subsided below sea level in the early Miocene; most rapid subsidence occurred during the early to middle Miocene. Submergence progressed seaward so that the last vestige of the Oyashio landmass, which is now under the upper trench slope, was below sea level in the latest Miocene. Sediment sources to the outer fore-arc basin changed progressively from lithic, predominantly nonvolcanic material derived from the uplifted landmass during the late Paleogene-early Neogene to volcanic, arc-derived sediment rich in volcanic glass, Plagioclase, and volcanic lithic fragments. The volcaniclastic sediment was probably derived both from Honshu to the west and Hokkaido to the northwest.In response to subsidence the sedimentary depocenters in the fore-arc basin migrated generally seaward through time; the greatest relative seaward migration occurred between the late Miocene and Pliocene. Thick sediment sequences accumulated in slope basins on the trench inner slope. Sediment from the arc moved seaward to spill over the slope via large channels.An abrupt change in morphology and patterns of sedimentation apparently took place in the late Pliocene, coincident with a peak in explosive volcanism recorded in the form of ash layers and increased glass contents in sediment. The deep sea terrace was uplifted several hundreds of meters and a major channel crossing the fore-arc region was tilted landward and filled. At about the same time the midslope terrace basin was created and began rapidly accumulating sediment. The older basins, lower on the trench inner slope, were destroyed, possibly by steep seaward tilting, or filled. Large slump masses were sloughed-off downslope to the trench. Little sediment now accumulates on the trench inner slope in the vicinity of the sites, and older strata crop out on the slope. The locus of deposition has shifted northward off Hokkaido where a large channel feeds sediment to the slope. Large slump masses now fill the trench and are being accreted, creating a "toe" to the slope in this region.

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“…3. The foci obtained in this study in a vertical E-W section of the crustal structure off northern Honshu (MuRAUCxi et al, 1977;LUDWIG et aL, 1966). The sense of faulting is indicated by the arrows for the normal fault events (1-5).…”

Section: Resultsmentioning

confidence: 99%

“…Discussion 4.1 Structure of the outer trench wall The major fault pattern in the outer slope of the Japan trench consists of fault sieps and horst-graben structures striking parallel or sub-parallel to the trench (LUDWIG et al, 1966;TAMAKI et al, 1977;IWABUCHI, 1980;SHIPBOARD SCIENTIFIC PARTY, 1980;KOBAYASHI et al, 1987;. This faulting pattern has been ascribed to bending of the plate prior to subduction (e.g., LUDWIG et al, 1966). The normal faulting caused by Events 1-5 includes both senses of motion: the arcside and sea-side are both downthrown.…”

Section: Event 3 (1969 08 24 22 03 M_b=52)mentioning

confidence: 99%

Faulting caused by earthquakes beneath the outer slope of the Japan trench.

Seno

Gonzalez

1987

J,Phys,Earth

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We determined fault plane solutions and focal depths for seven events which occurred in the Japan trench outer slope, using comparison between synthetic and observed long-and short-period teleseismic seismograms. The five normal fault solutions obtained in this study have nearly vertical nodal planes parallel to the trench and their depth range, 2-16 km below the seafloor, is in accord with bending of the oceanic lithosphere prior to subduction. The occurrence of both types of normal faulting, downthrow of both the continental and oceanic sides, is likely to be associated with the formation of horst-graben structures in the outer trench slope near the trench axis.One normal fault solution (31 km below the seafloor) that is significantly deeper than the other normal fault solutions has a nearly vertical nodal plane striking parallel to the ENE magnetic anomaly lineations in the region. This event is also characterized by its lower stress drop or slower rupture than the other events. This event would represent a reactivation of the initial structural fabric inherited from the accretion at the mid-oceanic ridge and indicates that the bending stress is small at this depth. One reverse fault solution, 41 km below the seafloor, is in accord with the compressional bending stress in the deeper portion of the lithosphere. These events indicate that a neutral surface of bending stress is around 30 km depth in this region at least for the past few decades, consistent with the elastic thickness of lithosphere in adjacent regions. This implies that the lithosphere is not entirely in deviatoric tension in this region, suggesting that the 1933 Sanriku earthquake may be a large bending event.

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Sediments and structure of the Japan Trench

Cited by 247 publications

References 15 publications

Site 28

Site 28

Sedimentary Evolution of the Japan Fore-Arc Region off Northern Honshu, Legs 56 and 57, Deep Sea Drilling Project

Faulting caused by earthquakes beneath the outer slope of the Japan trench.

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