scholarly journals Seafloor Topography Caused by Plate Bending Just Prior to Subduction, Observed at the Pacific Plate off the North-eastern Japan Arc

2017 ◽  
Vol 126 (2) ◽  
pp. Cover02_01-Cover02_02
Keyword(s):  
Pacific Plate ◽  
Plate Bending ◽  
Seafloor Topography ◽  
The North ◽  
The Pacific ◽  
North Eastern ◽  
Eastern Japan

scholarly journals THE INTRAPLATE VOLCANO-TECTONIC ACTIVITY IN NORTH-EASTERN AND SOUTH SECTORS OF THE PACIFIC LITHOSPHERIC PLATES WITH THE CONNECTION OF THE CHANGE OF ITS RELATIVE MOTION

2021 ◽  
Vol 49 (4) ◽  
pp. 102-127
Author(s):  
E. G. Mirlin ◽  
T. I. Lygina ◽  
E. I. Chesalova
Keyword(s):  
Relative Motion ◽  
Sedimentary Cover ◽  
Oceanic Lithosphere ◽  
Pacific Plate ◽  
Fault System ◽  
Tectonic Activity ◽  
The North ◽  
The Pacific ◽  
North Eastern ◽  
Absolute Age

The analysis of altimetric data in combination with bathymetry and gravimetry materials in the north-eastern and southern sectors of the Pacific Ocean, as well as detailed data on the underwater relief, the structure of the sedimentary cover, the composition and absolute age of basalts obtained within the area of domestic geological exploration for ferromanganese nodules (the Clarion-Clipperton zone) is carried out. Structural trends formed by local cone-shaped local structures of presumably volcanic nature, grouped along transform faults belonging to various stages of the kinematics of the Pacific Plate, have been traced in the structure of the oceanic lithosphere at various scale levels. The first trend corresponds to the extension of the fault system corresponding to the spreading system on the crest of the East Pacific rise before the restructuring of its planned geometry in the Paleocene-Eocene, the second coincides with their extension after the change in the relative movement of the Pacific Plate. The trends are characterized by planned disagreement, and an increase in the number of seamounts is observed in the areas of their intersection. Within the area of detailed studies, obvious signs of volcanic-tectonic activity were revealed: high dissection of the underwater relief, hills of different heights with steep slopes, whose volcanic nature is confirmed by differentiated basalts raised from their slopes, the absolute age of which indicates the multistage outpourings that occurred in an intraplate environment. The angular velocity of rotation of the spreading axis and the linear velocity of its advance with changes in the kinematics of the Pacific plate are estimated and possible reasons for changes in its relative motion are considered. An improved scheme of adaptation of the spreading zone to a change in the direction of relative plate movement is proposed, acc0ording to which an essential factor of intraplate volcanic-tectonic activity is the relaxation of stresses in the plate caused by external influence on it.

Structural Characteristics and Mechanism of the Horsetail Structure in China Offshore Basins: Case Studies from Liaodong Bay Area, Bohai Bay Basin and Weixinan Area, Beibuwan Basin

2020 ◽  
Author(s):  
Jie Zhang ◽  
Zhiping Wu ◽  
Yanjun Cheng
Keyword(s):  
Structural Characteristics ◽  
Strike Slip ◽  
Pacific Plate ◽  
Strike Slip Fault ◽  
Bohai Bay ◽  
Liaodong Bay ◽  
Clockwise Rotation ◽  
Bay Area ◽  
The North ◽  
The Pacific

<p>The horsetail structure, also named brush structure, generally refers to a sets of secondary faults converged to the primary fault on the plane. Based on 2-D and 3-D seismic data, the structural characteristics, evolution and mechanism of the horsetail structure of Liaodong Bay area in Bohai Bay Basin and Weixinan area in Beibuwan Basin are analyzed. In the Liaodong Bay area, the primary fault of the horsetail structure is the NNE-striking branch fault of Tan-Lu strike-slip fault zone. The NE-striking secondary extensional faults converged to the primary strike-slip fault. Fault activity analysis shows that both the primary and secondary faults intensively activated during the third Member of the Shahejie Formation (42~38 Ma). In the Weixinan area, the NE-striking Weixinan fault is the primary fault of the horsetail structure, which is an extensional fault. A large amount of EW-striking secondary extensional faults converged to the primary NE-striking Weixinan fault. Fault activity analysis shows that NE-striking primary fault intensively activated during the second Member of the Liushagang Formation (48.6~40.4 Ma), whereas the EW-striking secondary faults intensively activated during the Weizhou Formation (33.9~23 Ma). The different structure and evolution of the horsetail structure in the Liaodong Bay area and Weixinan area are mainly resulted from the regional tectonic settings. About 42 Ma, the change of subduction direction of the Pacific plate and the India-Eurasian collision resulted in the right-lateral strike-slip movement of NNE-striking Tan-Lu fault and the formation of NE-striking extensional faults along the bend of the strike-slip fault, therefore, the horsetail structure of Liaodong Bay area formed. However, the formation of the horsetail structure of Weixinan area is related to the clockwise rotation of extension stress in the South China Sea (SCS): 1) During Paleocene to M. Eocene (65~37.8 Ma), the retreat of Pacific plate subduction zone resulted in the formation of NW-SE extensional stress field in the north margin of the SCS, NE-striking primary fault of horsetail structure formed; 2) During L. Eocene to E. Oligocene (37.8~28.4 Ma), the change of subduction direction of the Pacific plate and the India-Eurasian collision resulted in the clockwise rotation of extension direction from NW-SE to N-S in the north margin of the SCS, a large amount of EW-striking secondary faults of horsetail structure formed, and the horsetail structure was totally formed in the Weixinan area until this stage.</p>

scholarly journals Possibility of recovery of slip deficit rate between the North American plate and the Pacific plate off Sanriku, northeast Japan

2007 ◽  
Vol 34 (20) ◽  
Author(s):  
Shinzaburo Ozawa ◽  
Hisashi Suito ◽  
Takuya Nishimura ◽  
Mikio Tobita ◽  
Hiroshi Munekane
Keyword(s):  
North American ◽  
Pacific Plate ◽  
North American Plate ◽  
The North ◽  
Slip Deficit ◽  
The Pacific ◽  
Off Sanriku

scholarly journals Radionuclide contamination in flood sediment deposits in the coastal rivers draining the main radioactive pollution plume of Fukushima Prefecture, Japan (2011–2020)

2021 ◽  
Vol 13 (6) ◽  
pp. 2555-2560
Author(s):  
Olivier Evrard ◽  
Caroline Chartin ◽  
J. Patrick Laceby ◽  
Yuichi Onda ◽  
Yoshifumi Wakiyama ◽  
...  
Keyword(s):  
Nuclear Power ◽  
Artificial Radionuclide ◽  
Radionuclide Contamination ◽  
Sediment Deposits ◽  
The Pacific ◽  
North Eastern ◽  
Coastal Rivers ◽  
The Pacific Ocean ◽  
River Catchments ◽  
Eastern Japan

Abstract. Artificial radionuclides including radiocesium (134Cs and 137Cs) and radiosilver (110mAg) were released into the environment following the Fukushima Dai-ichi nuclear power plant accident in March 2011. These particle-bound substances deposited on soils of north-eastern Japan, located predominantly within a ∼3000 km2 radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset (Evrard et al., 2021), which can be accessed at https://doi.org/10.1594/PANGAEA.928594, compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations across catchments draining ∼6450 km2 during 16 fieldwork campaigns. These campaigns were conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.

scholarly journals A Microearthquake Study of the Plate Boundary, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Martin Everardus Reyners
Keyword(s):  
Plate Boundary ◽  
Pacific Plate ◽  
Focal Mechanisms ◽  
Phase Changes ◽  
Indian Plate ◽  
Depth Range ◽  
The North ◽  
The Pacific ◽  
Deep Activity ◽  
Set Up

<p>The seismicity, structure and tectonics of the North Island plate boundary have been studied by means of a microearthquake traverse oriented in the direction of dip of the subducted Pacific plate and stretching from southern Hawke's Bay to northern Taranaki. The geometry of the top of the Pacific plate is inferred from a band of concentrated microearthquake activity which can be identified with the crust of the plate. The Pacific plate appears to have two knee-like bends, one between the east coast and the Ruahine Range, where the top of the plate is about 25 km deep, the other below the volcanic front, where it is about 70 km deep. The shallower bend and subsequent restraightening of the plate can be related to phase changes in the plate, while the deeper bend can be related to volcanism. Composite focal mechanisms indicate that seaward of its shallower bend the Pacific plate is being loaded by the Indian plate, whereas landward of this bend the Pacific plate is sinking under its own weight. Both composite focal mechanisms and the distribution of microseismicity in the Pacific plate suggest the existence of a major discontinuity striking down the dip of the plate and passing beneath the Tongariro volcanic centre. A conspicuous lack of microseismicity in the Indian plate in the eastern North Island revealed in this study can be related to the plates being unlocked in this region. A feature of the seismicity of the Indian plate in the region of the Wanganui Basin is the concentration of activity in the 25-42 km depth range, shallower activity being largely confined to the northeast edge of the basin, near Mt Ruapehu and Waiouru. Composite focal mechanisms suggest the 25-42 km deep activity reflects stresses set up by locking and unlocking of the plates, while the shallower activity reflects local stresses related to volcanic phenomena.</p>

New paedomorphic brachiopods from the abyssal zone of the north-eastern Pacific Ocean

Zootaxa ◽  
2013 ◽  
Vol 3613 (3) ◽  
pp. 281-288 ◽  
Author(s):  
MARIA ALEKSANDRA BITNER ◽  
VJACHESLAV P. MELNIK ◽  
OLGA N. ZEZINA
Keyword(s):  
Pacific Ocean ◽  
Deep Sea ◽  
New Genera ◽  
Eastern Pacific Ocean ◽  
The North ◽  
The Pacific ◽  
North Eastern ◽  
The Pacific Ocean ◽  
Abyssal Zone ◽  
Sexually Mature

New Recent very small but sexually mature brachiopods have been found at abyssal depths (4580–4850 m) in the Clarion- Clipperton Zone of the Pacific Ocean. They are characterized by simple (under-developed, juvenile) morphological fea-tures, which are interpreted here as paedomorphic, indicating the importance of heterochrony in the evolution of deep-sea brachiopods. We have described these brachiopods as representing two new genera and species, i.e. Oceanithyris juveni-formis Bitner & Zezina (Family ?Dyscoliidae) and Simpliciforma profunda Bitner & Zezina (Superfamily Gwynioidea).

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