scholarly journals SEISMOTECTONIC DEFORMATIONS IN THE PACIFIC AND OKHOTSK LITHOSPHERIC PLATES CONTACT ZONE

2021 ◽  
Vol 2 (2) ◽  
pp. 9-16
Author(s):  
Natalia A. Bushenkova ◽  
Olga A. Kuchay
Keyword(s):  
Deformation Field ◽  
Depth Range ◽  
Submerged Plate ◽  
The Pacific ◽  
Lithospheric Plates ◽  
Deformation Features ◽  
Field Uniformity ◽  
Deep Layers ◽  
Subducting Plate ◽  
Plate Geometry

The seismotectonic deformations were determined in the Pacific and Okhotsk (Eurasian) lithospheric plates subduction zone based on 2458 mechanisms of earthquake foci data for 1977-2019. The deformation features of medium in different deep layers are shown. The deformation field uniformity in the depth range of 1-70 km and the deformation field inhomogeneity for the submerged plate deep parts (105-200, 200-400 and 400-700 km) are revealed. One of the deformations field change reasons is the influence of ascending and, especially, descending currents of thermogravitational convection in the upper mantle sublithospheric part, in particular, the convection structure influence on the subducting plate geometry

A Quantitative Micro-Deformation Field Study of Shape Memory Alloys by High Sensitivity Moiré

1996 ◽  
Vol 459 ◽  
Author(s):  
Q. P. Sun ◽  
Terry T. Xu ◽  
X. Y. Zhang ◽  
P. Tong
Keyword(s):  
Single Crystal ◽  
Shape Memory ◽  
Deformation Behavior ◽  
Lattice Distortion ◽  
High Sensitivity ◽  
Tensile Specimen ◽  
Deformation Field ◽  
Uniaxial Tensile ◽  
Deformation Features ◽  
Micro Deformation

ABSTRACTQuantitative micro-macro combined experimental research on the deformation field of single crystal CuAINi shape memory alloy (SMA) is performed by using high sensitivity Moiré technique. The study is focused on the micro-macro correspondence of the deformation behavior of single crystal uniaxial tensile specimen during stress induced forward and reverse transformations. The aim of the experiment is to quantitatively relate the macroscopic applied stress with the deformation field in the mesoscale. The large deformation due to the lattice distortion during transformation was first successfully recorded by Moiré interferometry. Some important microstructure-related deformation features of single crystal SMA under uniaxial tension are first reported.

scholarly journals Annual Reversal of the Equatorial Intermediate Current in the Pacific: Observations and Model Diagnostics

2010 ◽  
Vol 40 (5) ◽  
pp. 915-933 ◽  
Author(s):  
Frédéric Marin ◽  
Elodie Kestenare ◽  
Thierry Delcroix ◽  
Fabien Durand ◽  
Sophie Cravatte ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Depth Range ◽  
Annual Variability ◽  
The Pacific ◽  
Adcp Observations ◽  
Vertically Propagating ◽  
Equatorial Rossby Wave ◽  
The Western Pacific ◽  
The Tropical Pacific ◽  
Equatorial Intermediate Current

Abstract A large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western Pacific Ocean between 2°S and the equator [from 26.2 Sv (1 Sv ≡ 106 m3 s−1) eastward in October 1999 to 28.6 Sv westward in April 2000]. To document this reversal and assess its origin, an unprecedented collection of ADCP observations of zonal currents (2004–06), together with a realistic OGCM simulation of the tropical Pacific, was analyzed. The results of this study indicate that this reversal is the signature of intense annual variability in the subsurface zonal circulation at the equator, at the level of the Equatorial Intermediate Current (EIC) and the Lower Equatorial Intermediate Current (L-EIC). In this study, the EIC and the L-EIC are both shown to reverse seasonally to eastward currents in boreal spring (and winter for the L-EIC) over a large depth range extending from 300 m to at least 1200 m. The peak-to-peak amplitude of the annual cycle of subthermocline zonal currents at 165°E in the model is ∼30 cm s−1 at the depth of the EIC, and ∼20 cm s−1 at the depth of the L-EIC, corresponding to a mass transport change as large as ∼100 Sv for the annual cycle of near-equatorial zonal transport integrated between 2°S and 2°N and between 410- and 1340-m depths. Zonal circulations on both sides of the equator (roughly within 2° and 5.5° in latitude) partially compensate for the large transport variability. The main characteristics of the annual variability of middepth modeled currents and subsurface temperature (e.g., zonal and vertical phase velocities, meridional structure) are consistent, in the OGCM simulation, with the presence, beneath the thermocline, of a vertically propagating equatorial Rossby wave forced by the westward-propagating component of the annual equatorial zonal wind stress. Interannual modulation of the annual variability in subthermocline equatorial transport is discussed.

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>

Biology and Management of Dogfish Sharks

2009 ◽  
Keyword(s):  
Kuril Islands ◽  
Spiny Dogfish ◽  
Depth Range ◽  
Southeastern Kamchatka ◽  
Pacific Waters ◽  
The Pacific ◽  
Body Weights ◽  
Northern Kuril Islands ◽  
Catch Rates ◽  
The Northern Kuril Islands

Abstract.—Spiny dogfish <em>Squalus acanthias </em>are occasionally caught by bottom trawls in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka. Only 23 specimens were captured during 8 years of commercial and research cruise observations from 1993 to 2000. This species occurred most frequently off the southeastern coast of Kamchatka within a depth range of 200–300 m and a bottom temperature range of 2°–3°C. In the study area, this shark was represented by specimens with total lengths of 54–85 cm (69.2 cm average) and body weights of 1–3 kg (1.8 kg average). Dogfish were captured in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka from July to December. Maximum catch rates occurred in November and were probably related to southward migrations.

scholarly journals Flatfish (Pleuronectiformes) species richness and depth distribution in the Gulf of Nicoya, Golfo Dulce, and two adjacent areas on the Pacific coast of Costa Rica

2020 ◽  
Vol 68 (4) ◽  
Author(s):  
Jose Vargas ◽  
Ana Rosa Ramírez ◽  
Berny Marín ◽  
Myrna López ◽  
Matthias Wolff
Keyword(s):  
Costa Rica ◽  
Pacific Coast ◽  
Depth Distribution ◽  
Depth Range ◽  
Low Oxygen ◽  
Good Opportunity ◽  
Tropical Regions ◽  
The Pacific ◽  
Region Data ◽  
Gulf Of Nicoya

Abstract: Flatfish diversity and depth distribution in the Gulf of Nicoya, Golfo Dulce, and two adjacent areas on the Pacific coast of Costa Rica. Introduction. Information on flatfish diversity and depth distribution is scarce for the Eastern Tropical Pacific. Historical data is important to evaluate changes in ecosystems due to local, regional and global stressors. Objective. To provide information on the presence, depth distribution and lengths of flatfish species collected by trawl nets. Methods. Fish studies were conducted by trawling at four sites along the Pacific coast of Costa Rica by the survey vessels Skimmer (1979-1989), Nishin Maru (1987-1988) and Victor Hensen (1993-1994). The published lists of species were consulted, museum specimens were accessed, and a list of flatfishes assembled. Results. A total of 36 species were found at the four sites over a depth range of 8 to 359 m. The family Paralichthyidae included 13 species followed by the Cynoglossidae with 12 species. Achiridae had six and Bothidae had five. The most speciose genus was Symphurus with 12 species. Thirty-five species were collected at depths from 10 to 235 m in the Gulf of Nicoya and Golfo Dulce. The Gulf of Nicoya estuary yielded 27 species during the Skimmer expedition and over a depth range of 8 to 60 m, while 31 species were found there during the V. Hensen survey at depths from 10 to 228 m. The V. Hensen survey in Golfo Dulce (20 to 235 m) captured 19 species, and 17 in Coronado Bay (21 to 187 m). Off the Nicoya Peninsula (56 to 359 m) 13 species were collected by the Nishin Maru shrimp trawler. A total of 21 species (58 %) were found at depths greater than 100 m and were probably exposed the low oxygen concentrations characteristic of hypoxia. During the V. Hensen survey Symphurus chabanaudi and S. elongatus were captured more frequently in the Gulf of Nicoya, while S. leei was so in Golfo Dulce. Cluster analyses based on presence-absence data for the Gulf of Nicoya and Golfo Dulce revealed low station similarity indicating habitat partitioning among the species. The size (Total length) of 33 species measured from both the Gulf of Nicoya and Golfo Dulce ranged from 8 cm (Syacium cf longidorsale, Trinectes xanthurus) to 50 cm (S. ovale). Only 12 species were found with lenghts over 20 cm. Of the species collected, A. mazatlanus (30 cm) and S. ovale (50) appear to be length records for the region. Data on flatfish landings by the semi-industrial fishing fleet for the period 2000-2016 indicates that this group represents less than 1% of the total landings (shrimp and bycatch), with a minimum of 365 kg in 2001 and a maximum of 13.414 kg in 2013. Conclusions. The diversity of the flatfish fauna of the Pacific coast of Costa Rica appears relatively high but comparable to that found in other tropical regions. The number of trawling ships has declined significantly on the Pacific coast of Costa Rica after 2014. This reduced fishing impact on the populations provides a good opportunity for updating the trophic models available for both the Gulf of Nicoya and Golfo and their use as tools for better management of the ecosystems.

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>

Centrifuge Experiments of the Initiation of Self-Sustaining Subduction

2021 ◽  
Author(s):  
Yossi Mart ◽  
Liran Goren ◽  
Einat Aharonov
Keyword(s):  
Subduction Zones ◽  
Lateral Force ◽  
Cardinal Process ◽  
Lithospheric Plates ◽  
Weakness Zone ◽  
Subducting Plate ◽  
Break Up ◽  
Back Arc ◽  
Analog Models ◽  
Analog Experiments

&lt;p&gt;The post-Triassic age of all oceanic lithospheres indicates the efficiency and the sustainability of lithospheric subduction, which consumes the basaltic seafloor and recirculates it in the upper mantle. Since at present the initiation of subduction is very rare, comprehension of this cardinal process should be carried through modeling &amp;#8211; numeric or analog. While deciphering processes through numeric modeling is commonly comprehensive, the analog models can determine major factor that constrain a tectonic procedure. Analog centrifuge experiments were applied to initiate self-sustained modelled subduction, trying to determine the critical factors that trigger its early stages.&lt;/p&gt;&lt;p&gt;Analytically we presumed that where densities of two lithospheric plates, juxtaposed across a weakness zone, exceed a critical value, then the denser lithosphere eventually will drive underneath the lighter one, provided the friction across the interface is not too high.&amp;#160;Consequently, analog experiments were carried out in a centrifuge at acceleration of ca. 1000 g., deforming miniaturized models of three layers representing the asthenosphere, the ductile and the brittle lithosphere. The lithospheres were modeled to include lighter and denser components, juxtaposed along a slightly lubricated contact plane, where the density difference between these components was ca. 200 kg/m&lt;sup&gt;3&lt;/sup&gt;. No mechanism of lateral force was applied in the experiment (even though such a vector exists in nature due to the seafloor spreading at the oceanic ridges), to test the possibility of subduction in domains where such a force is minor or non-existent.&lt;/p&gt;&lt;p&gt;The analog experiments showed that the penetration of the denser modeled lithosphere under the lighter one led to extension and subsequent break-up of the over-riding plate. That break-up generated seawards trench rollback, normal faulting, rifting, and formed proto-back-arc basins. Lateral differential reduction of the friction between the juxtaposed plates led to the development of arcuate subduction zones. The experimental miniaturization, and subsequent numerical and analytical modeling, suggest that the observed deformation in the analog models could be meaningful to the planet as well.&lt;/p&gt;&lt;p&gt;Constraints of the analog experimentation setting did not enable the modeling of the subduction beyond the initial stages, but there is ground to presume that at depths of 40-50 km, metamorphic processes of the generation of eclogites would change the initial mineralogy on the subducting plate. Reactions with water would convert basalts into metamorphic serpentinites and schists. Higher temperatures and pressures would melt parts of the subducted slab to generate felsic magmas, which would ascend towards the surface diapirically due to their lighter density. Alternately, low availability of H&lt;sub&gt;2&lt;/sub&gt;O would gradually alter the oceanic basalt and gabbro into eclogite, which would sink into the mantle due to its increased density.&lt;/p&gt;

Evaluation of the presence of a weak layer in the numerical simulation of lithospheric subduction

2020 ◽  
Author(s):  
Agustina Pesce ◽  
Victor Sacek
Keyword(s):  
Effective Viscosity ◽  
Oceanic Lithosphere ◽  
Time Range ◽  
Oceanic Plate ◽  
Continental Lithosphere ◽  
Slab Geometry ◽  
Weak Zone ◽  
Weak Layer ◽  
Lithospheric Plates ◽  
Subducting Plate

&lt;p&gt;One challenge to numerically simulate the subduction of cold oceanic lithosphere under continental lithosphere is the preservation of the decoupling between the subducting and upper plates for tens of millions of years. One strategy to simulate the persistence of the decoupling is the continuous entrainment of a weak layer (i.e. with low effective viscosity) at the top of the oceanic plate, representing a lubrication between both plates. However, variations on the thickness and rheological structure of this weak layer affect the geodynamic evolution of the subducting plate, modifying the geometry and degree of interactions between the lithospheric plates.&amp;#160;&lt;/p&gt;&lt;p&gt;In the present work we evaluated how the variation of the geometry, viscosity and density of the weak layer, relative to the surrounding lithosphere, can affect the lubrication between the two lithospheric plates. We performed a series of 2D numerical simulations using a finite element code for thermochemical convection. The code solves the Stokes flow for a fluid using the Boussinesq approximation in a Cartesian coordinate system, considering that the viscosity varies exponentially as a function of the temperature. In the present visco-plastic approach, the effective viscosity is determined by the combined effect of a viscous component, assuming the Frank-Kamenetskii rheology, and plastic deformation, following the Byerlee's friction law.&amp;#160;&lt;/p&gt;&lt;p&gt;In our numerical scenarios, the subduction is produced by the negative buoyancy of the cold oceanic lithosphere, without the imposition of an external velocity as boundary conditions. The time range of the simulation is of the order of 50 million years. In the initial simulation, a weak zone is imposed in the region between the two plates. This zone presents low viscosity and density relative to the surrounding lithosphere. As the oceanic slab is subducted, the weak zone is deformed and dragged. This removes the lubrication until utterly coupling the lithospheric plates, generating the thickening of the continental lithosphere below the trench region. To preserve the decoupling along all the simulation time, an extra continuous weak layer on top of the oceanic plate is added with low density and viscosity. In this scenario, the first weak zone is still dragged by the subducting plate, but the additional weak layer keeps a lubrication zone between the plates, preventing the coupling of the two lithospheric plates. Therefore, adding a continuous weak layer on top of the oceanic crust together with a weak zone prevents the coupling of the subducting and overriding plates when the effective viscosity of the weak layer is smaller than ~10&lt;sup&gt;19&lt;/sup&gt; Pa s. These numerical scenarios are used to analyse the subduction pattern of the Nazca plate observed in the southeastern portion of South America, using as constraints the slab geometry of the subducting oceanic plate derived from the Slab2 model.&lt;/p&gt;

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