Asymmetric dynamics at subduction zones: from plate kinematic constraints to global mantle convection

2021 ◽  
Author(s):  
Eleonora Ficini ◽  
Marco Cuffaro ◽  
Carlo Doglioni
Keyword(s):  
Mantle Convection ◽  
Subduction Zones ◽  
Numerical Models ◽  
Gravity Anomalies ◽  
Mass Conservation ◽  
Volume Estimation ◽  
Plate Convergence ◽  
Uplift Rates ◽  
The Difference ◽  
Subduction Rate

<p>The lithospheric sinking along subduction zones is part of the mantle convection. Therefore, computing the volume of lithosphere recycled within the mantle by subducting slabs quantifies the equivalent amount of mantle that should be displaced, for the mass conservation criterion. Starting from the analysis of the subduction hinge kinematics, that could either move towards (H-convergent) or away (H-divergent) with respect to the fixed upper plate, we compute the amount of lithosphere currently subducting below 31 subduction zones worldwide. Our results show that ~190 km<sup>3</sup>/yr and ~88 km<sup>3</sup>/yr of lithosphere are currently subducting below H-divergent and H-convergent subduction zones, respectively. This volume discrepancy is principally due to the difference in the two end-members subduction rate, that takes into account the hinge kinematics. We also propose supporting numerical models providing asymmetric volumes of subducted lithosphere, using the subduction rate,<sub> </sub>instead of plate convergence, as boundary condition. Subduction zones show a worldwide asymmetry from geological and geophysical observations, such as slab dip, structural elevation, gravity anomalies, heat flow, metamorphic evolution, subsidence and uplift rates or depth of the décollement planes. This asymmetry is expressed also in the behaviour of the subduction hinge, so that H-divergent subduction zones appears to be coincident with subduction zones having “westward”-directed slabs, whereas H-convergent are compatible with those that have “eastward-to-northeastward”-directed slabs. On the basis of this geographical polarity of subducting slabs, the obtained lithospheric volume estimation gives ~214 km<sup>3</sup>/yr and ~88 km<sup>3</sup>/yr of subducting lithosphere for subduction zones with W-directed and E-to-NE-directed slabs, respectively. This imply that W-directed subduction zones contribute more than twice in lithospheric sinking into the mantle with respect to E-to-NE-directed ones. In accordance with the conservation of mass principle, this volumetric asymmetry in the mantle suggests a displacement of ~120 km<sup>3</sup>/yr of mantle material from the west to the east, providing a constrain for a global asymmetric mantle convection.</p>

Numerical Model of Current Speed in Bojong Salawe Beach, Pangandaran West Java Province

2021 ◽  
Vol 2 (1) ◽  
pp. 17-23
Author(s):  
Subiyanto Subiyanto ◽  
Nira na Nirwa ◽  
Yuniarti Yuniarti ◽  
Yudi Nurul Ihsan ◽  
Eddy Afrianto
Keyword(s):  
Numerical Models ◽  
High Tide ◽  
Movement Pattern ◽  
Numerical Data ◽  
Current Speed ◽  
The West ◽  
Instantaneous Speed ◽  
The Difference ◽  
West Monsoon ◽  
Current Movement

The purpose of this study was to determine the hydrodynamic conditions at Bojong Salawe beach. The method used in this research is a quantitative method, where numerical data is collected to support the formation of numerical models such as wind, bathymetry, and tide data. The hydrodynamic model will be made using Mike 21 with the Flow Model FM module to determine the current movement pattern based on the data used. In the west monsoon with a maximum instantaneous speed of 0.04 - 0.08 m/s, while in the east monsoon it moves with a maximum instantaneous speed of 0,4 – 0,44 m/s. The dominant direction of current movement tends to the northeast. The results indicate the current speed during the east monsoon is higher than the west monsoon. The difference in the current speed is also influenced by the tide conditions; higher during high tide and lower during low tide. Monsoons also have a role in the current movements, though the effect is not very significant.

scholarly journals Numerical Study of Fracture Characteristics of Deep Granite Induced by Blast Stress Wave

2021 ◽  
Vol 2021 ◽  
pp. 1-22
Author(s):  
Zheming Zhu ◽  
Weiting Gao ◽  
Duanying Wan ◽  
Meng Wang ◽  
Yun Shu
Keyword(s):  
Shear Failure ◽  
Numerical Study ◽  
Numerical Models ◽  
Rock Fracture ◽  
Initial Pressure ◽  
3D Models ◽  
In Situ Stress ◽  
Vertical Pressure ◽  
The Difference ◽  
Radial Cracks

To study the characteristics of rock fracture in deep underground under blast loads, some numerical models were established in AUTODYN code. Weibull distribution was used to characterize the inhomogeneity of rock, and a linear equation of state was applied to describe the relation of pressure and volume of granite elements. A new stress initialization method based on explicit dynamic calculation was developed to get an accurate stress distribution near the borehole. Two types of in situ stress conditions were considered. The effect of heterogeneous characteristics of material on blast-induced granite fracture was investigated. The difference between 2D models and 3D models was discussed. Based on the numerical results, it can be concluded that the increase of the magnitude of initial pressure can change the mechanism of shear failure near the borehole and suppress radial cracks propagation. When initial lateral pressure is invariable, with initial vertical pressure rising, radial cracks along the acting direction of vertical pressure will be promoted, and radial cracks in other directions will be prevented. Heterogeneous characteristics of material have an obvious influence on the shear failure zones around the borehole.

Spectral modelling of mantle convection in a non orthogonal geometry: application to subduction zones

2000 ◽  
Vol 26 (7) ◽  
pp. 763-777
Author(s):  
D. Insergueix-Filippi ◽  
E. Tric ◽  
A. Batoul ◽  
G. Labrosse
Keyword(s):  
Mantle Convection ◽  
Subduction Zones ◽  
Orthogonal Geometry

The interplay between recycled and primordial heterogeneities: predicting Earth's mantle dynamics via numerical modeling

2021 ◽  
Author(s):  
Matteo Desiderio ◽  
Anna J. P. Gülcher ◽  
Maxim D. Ballmer
Keyword(s):  
Lower Mantle ◽  
Mantle Convection ◽  
Large Scale ◽  
Numerical Models ◽  
Bulk Composition ◽  
Oceanic Lithosphere ◽  
Mantle Dynamics ◽  
Density Anomaly ◽  
Mantle Mineral ◽  
Intrinsic Strength

<p>According to geochemical and geophysical observations, Earth's lower mantle appears to be strikingly heterogeneous in composition. An accurate interpretation of these findings is critical to constrain Earth's bulk composition and long-term evolution. To this end, two main models have gained traction, each reflecting a different style of chemical heterogeneity preservation: the 'marble cake' and 'plum pudding' mantle. In the former, heterogeneity is preserved in the form of narrow streaks of recycled oceanic lithosphere, stretched and stirred throughout the mantle by convection. In the latter, domains of intrinsically strong, primordial material (enriched in the lower-mantle mineral bridgmanite) may resist convective entrainment and survive as coherent blobs in the mid mantle. Microscopic scale processes certainly affect macroscopic properties of mantle materials and thus reverberate on large-scale mantle dynamics. A cross-disciplinary effort is therefore needed to constrain present-day Earth structure, yet countless variables remain to be explored. Among previous geodynamic studies, for instance, only few have attempted to address how the viscosity and density of recycled and primordial materials affect their mutual mixing and interaction in the mantle.</p><p>Here, we apply the finite-volume code <strong>STAGYY</strong> to model thermochemical convection of the mantle in a 2D spherical-annulus geometry. All models are initialized with a lower, primordial layer and an upper, pyrolitic layer (i.e., a mechanical mixture of basalt and harzburgite), as is motivated by magma-ocean solidification studies. We explore the effects of material properties on the style of mantle convection and heterogeneity preservation. These parameters include (i) the intrinsic strength of basalt (viscosity), (ii) the intrinsic density of basalt, and (iii) the intrinsic strength of the primordial material.</p><p>Our preliminary models predict a range of different mantle mixing styles. A 'marble cake'-like regime is observed for low-viscosity primordial material (~30 times weaker than the ambient mantle), with recycled oceanic lithosphere preserved as streaks and thermochemical piles accumulating near the core-mantle boundary. Conversely, 'plum pudding' primordial blobs are also preserved when the primordial material is relatively strong, in addition to the 'marble cake' heterogeneities mentioned above. Most notably, however, the rheology and the density anomaly of basalt affect the appearance of both recycled and primordial heterogeneities. In particular, they control the stability, size and geometry of thermochemical piles, the enhancement of basaltic streaks in the mantle transition zone, and they influence the style of primordial material preservation. These results indicate the important control that the physical properties of mantle constituents exert on the style of mantle convection and mixing over geologic time. Our numerical models offer fresh insights into these processes and may advance our understanding of the composition and structure of Earth's lower mantle.</p>

The importance of phase morphology for rheology of ferropericlase-bridgmanite mixtures

2021 ◽  
Author(s):  
Marcel Thielmann ◽  
Gregor Golabek ◽  
Hauke Marquardt
Keyword(s):  
Lower Mantle ◽  
Mantle Convection ◽  
Effective Viscosity ◽  
Large Scale ◽  
Numerical Models ◽  
Phase Morphology ◽  
Strong Impact ◽  
Analytical Approximations ◽  
The Impact ◽  
Strong Control

<p>The rheology of the Earth’s lower mantle is poorly constrained due to a lack of knowledge of the rheological behaviour of its constituent minerals. In addition, the lower mantle does not consist of only a single, but of multiple mineral phases with differing deformation behaviour. The rheology of Earth’s lower mantle is thus not only controlled by the rheology of its individual constituents (bridgmanite and ferropericlase), but also by their interplay during deformation. This is particularly important when the viscosity contrast between the different minerals is large. Experimental studies have shown that ferropericlase may be significantly weaker than bridgmanite and may thus exert a strong control on lower mantle rheology.</p><p>Here, we thus explore the impact of phase morphology on the rheology of a ferropericlase-bridgmanite mixture using numerical models. We find that elongated ferropericlase structures within the bridgmanite matrix significantly lower the effective viscosity, even in cases where no interconnected network of weak ferropericlase layers has been formed. In addition to the weakening, elongated ferropericlase layers result in a strong viscous anisotropy. Both of these effects may have a strong impact on lower mantle dynamics, which makes is necessary to develop upscaling methods to include them in large-scale mantle convection models. We develop a numerical-statistial approach to link the statistical properties of a ferropericlase-bridgmanite mixture to its effective viscosity tensor. With this approach, both effects are captured by analytical approximations that have been derived to describe the evolution of the effective viscosity (and its anisotropy) of a two-phase medium with aligned elliptical inclusions, thus allowing to include these microscale processes in large-scale mantle convection models.</p>

Geological signatures of slab shear-off during ongoing India-Asia convergence

2021 ◽  
Author(s):  
Abdul Qayyum ◽  
Nalan Lom ◽  
Eldert L Advokaat ◽  
Wim Spakman ◽  
Douwe J.J van Hinsbergen
Keyword(s):  
Numerical Models ◽  
Leading Edge ◽  
Plate Motion ◽  
Indian Plate ◽  
Mantle Structure ◽  
Continental Lithosphere ◽  
Common View ◽  
Plate Convergence ◽  
Collision Zone ◽  
The Himalaya

<p>Much of our understanding of the dynamics of slab break-off and its geological signatures rely on numerical models with a simplified set-up, in which slab break-off follows arrival of a continent in a mantle-stationary trench, the subsequent arrest of plate convergence, and after a delay time of 10 Ma or more, slab break off under the influence of slab pull. However, geological reconstructions show that plate tectonic reality deviates from this setup: post-collisional convergence is common, trenches are generally not stationary relative to mantle, neither before nor after collision, and there are many examples in which the mantle structure below collision zones is characterized by more, or fewer slabs than collisions.</p><p>A key example of the former is the India-Asia collision zone, where the mantle below India hosts two major, despite the common view of a single collision. Kinematic reconstructions reveal that post-collisional convergence amounted 1000s of kms, and was associated with ~1000 km of trench/collision zone advance. Collision between India-Asia collision zone may provide a good case study to determine the result of post-collisional convergence and absolute lower and upper plate motion on mantle structure, and to evaluate to what extent commonly assumed diagnostic geological phenomena of slab break-off apply.</p><p>In addition to the previously identified major India, Himalaya, and Burma slabs, we here map smaller slabs below Afghanistan and the Himalaya that reveal the latest phases of break-off. We show that west-dipping and east-dipping slabs west and east of India, respectively, are dragged northward parallel to the slab, slabs subducting north of India are overturned, and that the shallowest slab fragments are found in the location where the horizontally underthrust Indian lithosphere below Tibet is narrowest. Our results confirm that northward Indian absolute plate motion continued during two episodes of break-off of large (>1000 km wide) slabs, and decoupling of several smaller fragments. These slabs are currently found south of the present day trench locations. The slabs are located even farther south (>1000 km) of the leading edge of the Indian continental lithosphere, currently underthrust below Tibet, from which the slabs detached, signalling ongoing absolute Indian plate motion. We conclude that the multiple slab break-off events in this setting of ongoing plate convergence and trench advance is better explained by shearing off of slabs from the downgoing plate, possibly at a depth corresponding to the base of the Indian continental lithosphere, are not (necessarily) related to the timing of collision. A recently proposed, detailed diachronous record of deformation, uplift, and oroclinal bending in the Himalaya that was liked to slab break-off fits well with our kinematically reconstructed timing of the last slab shear-off, and may provide an important reference geological record for this process. We find that the commonly applied conceptual geological signatures of slab break-off do not apply to the India-Asia collision zone, or to similar settings and histories such as the Arabia-Eurasia collision zone. Our study provides more realistic boundary conditions for future numerical models that aim to assess the dynamics of subduction termination and its geological signatures.</p>

How HY-2A/GM altimeter performs in marine gravity derivation: assessment in the South China Sea

2019 ◽  
Vol 219 (2) ◽  
pp. 1056-1064 ◽  
Author(s):  
Chengcheng Zhu ◽  
Jinyun Guo ◽  
Cheinway Hwang ◽  
Jinyao Gao ◽  
Jiajia Yuan ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Gravity Anomalies ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Open Sea ◽  
Marine Gravity ◽  
Sea Surface Heights ◽  
The Difference

SUMMARY HY-2A is China's first satellite altimeter mission, launched in Aug. 2011. Its geodetic mission (GM) started from 2016 March 30 till present, collecting sea surface heights for about five 168-d cycles. To test how the HY-2A altimeter performs in marine gravity derivation, we use the least-squares collocation method to determine marine gravity anomalies on 1′ × 1′ grids around the South China Sea (covering 0°–30°N, 105°E–125°E) from the HY-2A/GM-measured geoid gradients. We assess the qualities of the HY-2A/GM-derived gravity over different depths and areas using the bias and tilt-adjusted ship-borne gravity anomalies from the U.S. National Centers for Environmental Information (NCEI) and the Second Institute of Oceanography, Ministry of Natural Resources (MNR) of P. R. China. The RMS difference between the HY-2A/GM-derived and the NCEI ship-borne gravity is 5.91 mGal, and is 5.33 mGal when replacing the HY-2A value from the Scripps Institution of Oceanography (SIO) V23.1 value. The RMS difference between the HY-2A/GM-derived and the MNR ship-borne gravity is 2.90 mGal, and is 2.76 mGal when replacing the HY-2A value from the SIO V23.1 value. The RMS difference between the HY-2A and SIO V23.1 value is 3.57 mGal in open sea areas at least 20 km far away from the coast. In general, the difference between the HY-2A/GM-derived gravity and ship-borne gravity decreases with decreasing gravity field roughness and increasing depth. HY-2A results in the lowest gravity accuracy in areas with islands or reefs. Our assessment result suggests that HY-2A can compete with other Ku-band altimeter missions in marine gravity derivation.

scholarly journals Illuminating subduction zone rheological properties in the wake of a giant earthquake

2019 ◽  
Vol 5 (12) ◽  
pp. eaax6720 ◽  
Author(s):  
Jonathan R. Weiss ◽  
Qiang Qiu ◽  
Sylvain Barbot ◽  
Tim J. Wright ◽  
James H. Foster ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Three Dimensional ◽  
Surface Strain ◽  
Postseismic Deformation ◽  
Crust And Upper Mantle ◽  
Plate Convergence ◽  
Maule Earthquake ◽  
History Of ◽  
Dependent Viscosity

Deformation associated with plate convergence at subduction zones is accommodated by a complex system involving fault slip and viscoelastic flow. These processes have proven difficult to disentangle. The 2010 Mw 8.8 Maule earthquake occurred close to the Chilean coast within a dense network of continuously recording Global Positioning System stations, which provide a comprehensive history of surface strain. We use these data to assemble a detailed picture of a structurally controlled megathrust fault frictional patchwork and the three-dimensional rheological and time-dependent viscosity structure of the lower crust and upper mantle, all of which control the relative importance of afterslip and viscoelastic relaxation during postseismic deformation. These results enhance our understanding of subduction dynamics including the interplay of localized and distributed deformation during the subduction zone earthquake cycle.

Curvature, a mechanical link between the geometrical complexities of a fault: application to bends, kinks and rough faults

2020 ◽  
Vol 223 (1) ◽  
pp. 211-232
Author(s):  
Pierre Romanet ◽  
Dye SK Sato ◽  
Ryosuke Ando
Keyword(s):  
Numerical Models ◽  
Slip Distribution ◽  
Unified Framework ◽  
New Approach ◽  
Fault Surface ◽  
Earthquake Mechanics ◽  
Analytical Perspective ◽  
The Difference ◽  
Field Lines ◽  
New Interpretation

SUMMARY Many recent studies have tried to determine the influence of geometry of faults in earthquake mechanics. However, it still remains largely unknown, and it is explored mainly with numerical models. In this paper, we will try to understand how exactly does the geometry come into play in the mechanics of an earthquake from analytical perspective. We suggest a new interpretation of the effect of geometry on the stress on a fault, where the curvatures of the fault that multiply the slip play a major role. Starting from the representation theorem, which links the displacement in a medium to the slip distribution on its boundary, and assuming a 3-D, homogeneous, infinite medium, a regularized boundary-element equation can be obtained. Using this equation, it is possible to separate the influence of geometry, as expressed by the curvatures and torsions of the field lines of slip on the fault surface, which multiply the slip, from the effect of the gradient of slip. This allows us to shed new light on the mechanical effects of geometrical complexities on the fault surface, with the key parameters being the curvatures and torsions of the slip field lines. We have used this new approach to show that, in 2-D static in-plane problems, the shear traction along the fault is mainly controlled by the gradient of slip along the fault, while the normal traction is mainly controlled by the slip that multiplies the curvature along the fault. Finally, we applied this new approach to re-interpret the effect of roughness (why there is a need for a minimum lengthscale in linear elasticity, how to study mechanically the difference of roughness measurements with the direction of slip, scaling of slip distribution versus geometry), bends and kinks (what is the difference between the two, are they sometimes equivalent), as well as to explain further the false paradox between smooth-and-abrupt-bends. This unified framework allows us to improve greatly our understanding of the effect of fault geometry on the mechanics of earthquakes.

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