scholarly journals Evolution of Subduction Cusps From the Perspective of Trench Migration and Slab Morphology

2021 ◽  
Vol 9 ◽  
Author(s):  
Hui Zhao ◽  
Xiaobing Shen ◽  
Wei Leng
Keyword(s):  
Numerical Model ◽  
Plate Boundary ◽  
Controlling Factors ◽  
Asymmetric Distribution ◽  
Evolutionary Pathway ◽  
Pull Force ◽  
Corner Angle ◽  
Plate Movement ◽  
Dip Angle ◽  
Continuous Plate

The geometries of trenches vary worldwide due to continuous plate boundary reorganization. When two trenches intersect to generate a corner, a subduction cusp is formed. Although subduction cusps are frequently observed throughout historical plate movement reconstructions, few studies have been conducted to explore the controlling factors of trench migration and slab morphology along subduction cusps. Here, we use a 3-D dynamic subduction model to explore the influence of the overriding plate strength, initial slab-pull force, and initial cusp angle on the evolution of subduction cusps. Our numerical model results suggest the following: 1) subduction cusps have a tendency to become smooth and disappear during the subduction process; 2) the slab dip angle is smallest in the diagonal direction of the subduction cusp, and a larger cuspate corner angle leads to a larger slab dip angle; 3) the asymmetric distribution of the overriding plate strength and initial slab-pull force determine the asymmetric evolutionary pathway of subduction cusps. Our results provide new insights for reconstructing the evolution of subduction cusps from seismological and geological observations.

scholarly journals Key Parameters of Roof Cutting of Gob-Side Entry Retaining in a Deep Inclined Thick Coal Seam with Hard Roof

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 934 ◽  
Author(s):  
Jinzhu Hu ◽  
Manchao He ◽  
Jiong Wang ◽  
Zimin Ma ◽  
Yajun Wang ◽  
...  
Keyword(s):  
Numerical Model ◽  
Coal Seam ◽  
Economic Benefits ◽  
Surrounding Rock ◽  
Thick Coal Seam ◽  
Hard Roof ◽  
Coal Recovery ◽  
Rock Structure ◽  
Different Depths ◽  
Dip Angle

Gob-side entry retaining by roof cutting (GERRC) employed in a deep inclined thick coal seam (DITCS) can not only increase economic benefits and coal recovery, but also optimize surrounding rock structure. In accordance with the principles of GERRC, the technology of GERRC in DITCS is introduced and a roof-cutting mechanical model of GERRC is proposed to determine the key parameters of the depth and angle of RC. The results show that the greater the RC angle, the easier the caving of the goaf roof, but the length of cantilever beam increases. The depth of RC should account for the dip angle of the coal seam when the angle is above 20°. Increasing the coal seam dip angle could reduce the volume of rock falling of the goaf roof, but increase the filling height of the upper gangue to slide down. According to numerical model analysis of the stress and displacement of surrounding rock at different depths and angles of RC, when the depth of RC increased from 9 m to 13 m, the distance between the stress concentration zone and the coal side is increased. When the angle of RC increased from 0° to 20°, the value of roof separation is decreased. GERRC was applied in a DITCS with 11 m depth and 20° RC angle, and the field-measured data verified the conclusions of the numerical model.

scholarly journals Roof Subsidence and Movement Law of Composite Strata Mining: Insights from Physical and Numerical Modeling

Minerals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 3
Author(s):  
Yongqian Wang ◽  
Xuan Wang ◽  
Jiasheng Zhang ◽  
Xiaobin Chen ◽  
Wujun Zhu ◽  
...  
Keyword(s):  
Numerical Model ◽  
Physical Model ◽  
Surface Subsidence ◽  
Similarity Criteria ◽  
Theoretical Formula ◽  
Constant Field ◽  
Rock Formations ◽  
Movement Characteristics ◽  
Similar Materials ◽  
Dip Angle

Sinking and horizontal movements are necessary parameters for assessing the potential impacts of surface subsidence in mining activities. Based on similarity criteria, the surface subsidence mechanism was studied using a physical model composed of similar materials such as sand, cement, and gypsum. With constant field geological parameters maintained in two angles of a coal seam, models of roof subsidence of composite rock were compared for different mining configurations. In accordance with observations from the physical model, it was concluded that subsidence and horizontal movement of strata near to and far from the coal seams were different and divided into five zones. The zone above a mined-out area underwent greater total subsidence compared to unexploited regions on both sides. Correlations between a subsidence curve and the height of a caving zone and the mining dip angle were obtained and verified from numerical model results. According to the roof’s position relative to the goaf, the area above the goaf of the composite rock layer was divided into three regions: a curving zone, a water-conducting fracture zone, and a falling zone, to which the subsidence and movement characteristics of each area could be proposed. Compared with the subsidence and movement characteristics observed from the physical and numerical model, the acquisition of subsidence characteristics and parameters in different areas can provide an idea for improvement, innovation or proposal of a theoretical formula for subsidence prediction of composite rock formations.

The Indus Suture Line, the Himalaya, Tibet and Gondwanaland

1974 ◽  
Vol 111 (5) ◽  
pp. 369-383 ◽  
Author(s):  
A. R. Crawford
Keyword(s):  
Western Australia ◽  
Tarim Basin ◽  
Plate Boundary ◽  
Continental Drift ◽  
Suture Line ◽  
Tien Shan ◽  
Plate Movement ◽  
Terrestrial Vertebrate ◽  
History Of ◽  
The Himalaya

SummaryMisunderstanding exists about the origin of the Himalaya, Indo-Tibetan relationships and the extent and history of Gondwanaland. The Indus Suture Line is a relic of fracture to the mantle but for a period only represented by the faunas of the ‘exotic blocks’ of the Tibetan Himalaya, i.e. Permian—Late Jurassic. Tibet appears originally to have been part of a plate including India, but submerged while India remained continental. Associated with the fracture extending to the mantle represented now by the Indus Suture Line, shallower subparallel fractures developed within which the Gondwana sediments of the Himalaya were preserved. These, together with the salt at the base of the Tethyan marine sequence, facilitated intra-continental orogeny when, much later, India was affected by vigorous sea-floor spreading and plate movement in the NW Indian ocean after it had become attached to Asia.The northern plate boundary was beyond Tibet, on the N side of the Tarim Basin Block, and along the Tien Shan. The Tien Shan present peculiar features, particularly very deep long intramontane depressions such as Issyk Kul in USSR and Turfan-Hami in China, and their stratigraphy shows persistent mobility. The Tarim Basin Block has moved sinistrally relative to Tibet and in Gondwanaland lay near northern Western Australia. The suggested extent of Gondwanaland explains the present lack of continental crust W of Western Australia, now in Tibet, and the intracontinental origin of the Himalaya is consistent with the absence of recent volcanism in an area of considerable seismicity. The association of Tibet with India in Gondwanaland destroys the effectiveness of arguments against continental drift based upon the extension of Indian stratigraphic sequences across the Himalaya. The hypothesis of an enlarged Gondwanaland is given support by recent Chinese discoveries of terrestrial vertebrate fossils of Gondwanic type near the Tien Shan.

Distribution Characteristics of Fractures in the Ultra-Low Permeability Reservoirs of Anpeng Oilfield, China

2014 ◽  
Vol 909 ◽  
pp. 463-466
Author(s):  
Lei Gong ◽  
Shu Jun Guo ◽  
Shuai Gao ◽  
Xian Xian Tao ◽  
Jian Guo Huang
Keyword(s):  
Tectonic Stress ◽  
Controlling Factors ◽  
Low Permeability ◽  
Distribution Characteristics ◽  
Thin Sections ◽  
Main Fracture ◽  
Main Factors ◽  
Dip Angle ◽  
Fracture Distribution ◽  
Low Permeability Reservoirs

Using the data of cores, outcrops, thin sections and image logs, we analyzed the fracture distribution characteristics in the ultra-low permeability reservoirs of Anpeng oilfield. Then, we analyzed the main factors controlling the development of fractures. There are tectonic fractures and diagenetic fractures in the ultra-low permeability reservoirs. Tectonic fractures with high dip-angle are the main fracture type. Under the stresses resulting from horizontal tectonic compressions in the Early and Late Himalayan movements, three sets of tectonic fractures formed in the study area, i.e. E-W, NE-SW and NW-SE orientations. The E-W oriented fractures are developed better, then the NE-SW and NW-SE oriented fractures. The formation and distribution of these tectonic fractures are controlled by the tectonic stress field, lithology, porosity, permeability, layer thickness and structures. Under the same controlling factors, the origin types, occurrences and development characteristics of fractures in shallow-to mid-depth reservoirs are similar to that in the deep reservoirs. But fractures developed better in the deep reservoirs than that in the shallow-to mid-depth reservoirs.

scholarly journals Simple Topographic Parameter Reveals the Along-Trench Distribution of Frictional Properties on a Shallow Plate Boundary Fault

2021 ◽  
Author(s):  
Hiroaki Koge ◽  
Juichiro Ashi ◽  
Jin-Oh Park ◽  
Ayumu Miyakawa ◽  
Suguru Yabe
Keyword(s):  
Spatial Distribution ◽  
Friction Coefficient ◽  
Subduction Zones ◽  
Slope Angle ◽  
Plate Boundary ◽  
Boundary Fault ◽  
Frictional Properties ◽  
Topographic Parameter ◽  
Dip Angle ◽  
Taper Model

Abstract The critical taper model of a sedimentary wedge best describes the first-order mechanics of a subduction zone wedge. The tapered wedge geometry, which is conventionally defined by two parameters, the slope angle and the basal dip angle, is responsible for the strength of a megathrust. By applying this theoretical model to subduction zones, fault frictional properties and earthquake occurrences can be compared among subduction zones, and within a single subduction zone, the spatial distribution or temporal change of fault strength can be investigated. The slope angle can be accurately estimated from bathymetry data, but the basal dip angle must be inferred from the subsurface structure, and it requires highly accurate depth-converted seismic reflection profiles. Thus, application of the critical taper model is often limited by a lack of a sufficient number of highly accurate profiles, and the spatial distribution of frictional coefficients must be inferred from relatively few data, generally less than a dozen points. To improve this situation, we revisited the theoretical formula of the critical taper model. We found that the effect of the décollement dip angle β on the critical taper model of a sedimentary wedge is negligible when the pore fluid pressure ratio is high or internal friction is small, conditions which are met in many subduction zones. Therefore, this finding allows frictional variation to be approximated by using only the slope angle variation obtained from the bathymetry. We applied this approximation to the Japan Trench as an example of this approximation, and were able to estimate the friction coefficient distribution on the shallow plate boundary fault from 71 data points. We found that the area where the friction coefficient was smaller than the mean corresponded to the segment where a large coseismic shallow rupture occurred during the 2011 Tohoku-oki earthquake (Mw 9.0). This result shows that by approximating tapered wedge geometry using a simple topographic parameter that can be obtained from existing global bathymetry, we can quickly estimate the distribution of frictional properties on a plate boundary fault along a trench and related seismic activity.

3D Wave Simulation Basing on VOF Method and Dynamic Grid Technology

2013 ◽  
Vol 774-776 ◽  
pp. 344-346
Author(s):  
Xu Sheng Wang ◽  
Lian Hai Wang ◽  
Xiu Fu Song ◽  
Bo Ning
Keyword(s):  
Numerical Simulation ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Sine Wave ◽  
Two Phase ◽  
Second Development ◽  
Wave Plate ◽  
Irregular Wave ◽  
Plate Movement ◽  
Influence Of Water

In order to investigate 3-D situation, the wind and the waves on the interaction on the influence of water object characteristics, this article through to the second development software Fluent, numerical simulation for 3D wave the dynamic process of the wave. First of all a three dimensional two phase numerical pool, the definition made wave plate boundary for movement, according to the characteristics of sine wave launch made wave plate movement rules, and through the user-defined function (UDF) DEFINE_CG_MOTION macro, realize the made the movement of wave plate, analyzes the cycle 2 s stroke 3 m and cycle 6.0 s stroke 0.5 m of sine wave. Second, blowing and horizontal plane Angle 45 ° 2.0 m/s wind, get the jump irregular wave wave process. The results found that reduce the maximum wind trough value, at the same time, improve the big wave peak, adding to the pool of wave, for numerical simulation of 3-d situation seas over deck, leak, prevent oil spill and the foundation animals.

scholarly journals New Zealand earthquakes and plate tectonic theory

1979 ◽  
Vol 12 (2) ◽  
pp. 87-93
Author(s):  
R. I. Walcott
Keyword(s):  
New Zealand ◽  
Relative Proportion ◽  
Plate Boundary ◽  
Plate Tectonic ◽  
Plate Movement ◽  
North East ◽  
The Pacific ◽  
Plate Boundary Zone ◽  
Seismic Deformation ◽  
Anelastic Deformation

The rates and direction of shear strain from geodetic data and the direction of slip from earthquake mechanism studies in New Zealand are
in good agreement with plate tectonic theory. The relative motion of
the Pacific and Indian plates in the last 100 years has been accommodated by distributed strain in a belt at least 100 km wide crossing New Zealand from north-east to south-west. Strain rates within this belt exceed
3 x 10-7/y and average 5 x 10-7/y in Marlborough. Under the eastern North Island and northern part of the South Island the Pacific plate underthrusts the overlying belt of deformation. Large thrust earthquakes are episodically generated, perhaps by locking of the thrust. Not all relative plate movement is transformed into displacement on faults - a substantial fraction is taken up by aseismic and anelastic deformation within the plate boundary zone. The relative proportion of aseismic and seismic deformation may vary in different regions.

Deconvolution of gamma‐ray logs in the case of dipping radioactive zones

Geophysics ◽  
1981 ◽  
Vol 46 (2) ◽  
pp. 198-202 ◽  
Author(s):  
John G. Conaway
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Gamma Ray ◽  
Experimental Studies ◽  
Borehole Diameter ◽  
Dip Angle ◽  
Gamma Ray Log ◽  
Simple Numerical Model

It has been shown both theoretically and experimentally that the grade‐thickness product of a zone of uranium or other radioelement, computed on the basis of a gamma‐ray log, will vary inversely with the cosine of the angle between the radioactive zone and the normal to the borehole. I present experimental studies in model boreholes containing dipping radioactive zones, extending the theory of deconvolution of gamma‐ray logs to the case of dipping zones. The experimental data were found to agree well with a simple numerical model which takes into account borehole diameter, detector length, and thickness of the radioactive zone as well as dip angle.

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