Sediments and Structure of the Japan Sea

Ludwig, W. J.; Murauchi, Sadanori; Houtz, Robert E.

doi:10.1130/0016-7606(1975)86<651:sasotj>2.0.co;2

Cited by 146 publications

(123 citation statements)

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“…3). This crustal thickness is similar to that observed at Site 795 (13.5-17 km) on the northern margin of the Japan Basin and is slightly less than that of the central Yamato Basin (18-19 km;Ludwig et al, 1975;Hirata et al, 1989). It is also considerably thicker than typical oceanic crust (5-10 km) but is not as thick as typical continental crust (30-35 km).…”

Section: Crustal Structuresupporting

confidence: 61%

“…4). The total crustal thickness below this bank is not well constrained but is on the order of 20 km (Ludwig et al, 1975). This estimate is much greater than typical oceanic crust but is still short of representative continental values.…”

Section: Crustal Structurementioning

confidence: 87%

“…Figure 3 summarizes the distributions, ages, and types of basement rocks which have been recovered by dredging operations in the vicinity of Site 797. Only those dated samples whose Ludwig et al (1975). B.…”

Section: °7mentioning

confidence: 99%

“…3 and 4). The second profile lies slightly northeast of the first and is constructed from Sonobuoy and two-ship refraction surveying (Ludwig et al, 1975;Figs. 3 and 4).…”

Section: Crustal Structurementioning

confidence: 99%

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Site 797

1990

Proceedings of the Ocean Drilling Program

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1 Tamaki, K., Pisciotto, K., Allan, J., et al., 1990. Proc. ODP, Init. Repts., 127: College Station, TX (Ocean Drilling Program). Principal results: The objectives at Site 797, located in the southern Yamato Basin, were (1) to determine the age and nature of acoustic basement, (2) to measure the direction and magnitude of the present stress field, and (3) to characterize the sedimentation, subsidence, and oceanographic evolution of the area. The results at Site 797 are summarized below and in Figure 1. The principal results at Site 797 are as follows:1. Acoustic basement and an overlying seismic interval at this site comprise basalts and dolerites and interlayered volcaniclastic sandstones, siltstones, and silty claystones. The age of the sediments which overlie the shallowest basalt layer is estimated to be about 19 Ma. Based on paleodepth estimates using microfossils within these sediments and the sedimentologic interpretation of the underlying volcaniclastic sediments, this part of the Yamato Basin probably subsided rapidly during the early Miocene. The uppermost basalts most likely represent submarine lava flows, whereas the bulk of the underlying igneous units are sills and dikes. The upper nine units are high-Al basalt in composition, consistent with generation during the early stages of arc rifting. However, the units below these are mildly alkaline basalts and enriched tholeiites, which are unrelated to the overlying basalts and were probably derived from a different mantle source.2. The in-situ stress field could not be determined, because poor hole conditions precluded packer/hydro fracture tests. A borehole televiewer log over one basalt interval showed fractures but no borehole breakouts for stress directions.3. The lithologic and paleontological data indicate at least four principal stages in the evolution of this part of the Yamato Basin: (a) an early Miocene period of submarine basaltic volcanism and concomitant deposition of gravity-flow and current-reworked volcani- 323 SITE 797clastic sandstones and siltstones on a shelf or slope, probably outboard of a delta; (b) a late early to early middle Miocene phase of diminishing submarine volcanic activity, warm surface waters, and deposition of calcareous and slightly phosphatic hemipelagic claystones at lower middle bathyal depths (1500-2000 m) in a poorly oxygenated basin; (c) a late Miocene to late Pliocene cooling period beginning with an interval of anomalously slow sedimentation (5 m/m.y.) or a hiatus and characterized by dominant but variable diatomaceous sedimentation at lower middle bathyal depths (1500-2000 m); and (d) a latest Pliocene to Holocene stage during which diatomaceous sedimentation diminished volcanic-ash production and terrigenous input increased, subsidence continued, and climate oscillated to produce a sequence of interlayered light-and dark-colored silty clays having variable organic-carbon contents. In contrast with the more northern sites drilled during Leg 127, the sediments at Site 797 contain more carbonate suggesting ...

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Section: Crustal Structuresupporting

confidence: 61%

Section: Crustal Structurementioning

confidence: 87%

Section: °7mentioning

confidence: 99%

“…3 and 4). The second profile lies slightly northeast of the first and is constructed from Sonobuoy and two-ship refraction surveying (Ludwig et al, 1975;Figs. 3 and 4).…”

Section: Crustal Structurementioning

confidence: 99%

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Site 797

1990

Proceedings of the Ocean Drilling Program

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“…It is obvious that the velocity structure in and around the aftershock area is laterally inhomogeneous (MURAUCHI, 1966;LUDWIG et al, 1975;YOSHII and ASANO, 1972). The most striking part is a gradual thickening of the crust from the sea to the land.…”

mentioning

confidence: 94%

Aftershock distribution of the 1983 Nihonkai-chubu (Japan Sea) earthquake determined from relocated hypocenters.

1986

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Seismic constraints of the formation process on the back‐arc basin in the southeastern Japan Sea

Sato

Kodaira

et al. 2014

JGR Solid Earth

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To clarify the formation process of the back-arc basin in the Japan Sea, which is located next to the northwestern Pacific, a seismic survey using ocean bottom seismographs and an air gun array was undertaken in areas from the northern Yamato Basin to the coast of the northeastern Japan Island Arc off Awa-shima Island. The crust beneath the northern Yamato Basin off Awa-shima Island is approximately 16 km thick. The upper and lower crusts are, respectively, about 5 km thick with a steep velocity gradient and about 10 km thick with a gentle velocity gradient. In the basin, there are very few units with P wave velocity of 5.4-6.0 km/s, corresponding to the continental upper crust. The crustal structure of the northern Yamato Basin has characteristics of thicker oceanic crust. The high-velocity lowermost crust in the northern Yamato Basin with 7.2-7.4 km/s might show melt formed by a slightly high mantle temperature during the opening of the basin. However, the crust beneath the areas from the Sado Ridge to the coast, which is approximately 25-26 km thick, is slightly thinner than that of the continental crust and island arc crust. The crustal structure beneath this area is inferred to be a rifted continental and/or a rifted island arc crust.

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Sediments and Structure of the Japan Sea

Cited by 146 publications

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Site 797

Site 797

Aftershock distribution of the 1983 Nihonkai-chubu (Japan Sea) earthquake determined from relocated hypocenters.

Seismic constraints of the formation process on the back‐arc basin in the southeastern Japan Sea

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