Improving subduction interface implementation in dynamic numerical models

Abstract. Numerical subduction models often implement an entrained weak layer (WL) to facilitate decoupling of the slab and upper plate. This approach is attractive in its simplicity, and can provide stable, asymmetric subduction systems that persist for many tens of millions of years. In this study we undertake a methodological analysis of the WL approach, and use these insights to guide improvements to the implementation. The issue that primarily motivates the study is the emergence of significant spatial and temporal thickness variations within the WL. We show that these variations are mainly the response to volumetric flux gradients, caused by the change in boundary conditions as the WL material enters and exits the zone of decoupling. The time taken to reach a quasi-equilibrium thickness profile will depend on the total plate convergence, and is around 7 Myr for the models presented here. During the transient stage, width variations along the WL can exceed 4×, which may impact the effective strength of the interface, through physical effects if the rheology is linear, or simply if the interface becomes inadequately numerically resolved. The transient stage also induces strong sensitivity to model resolution. By prescribing a variable-thickness WL at the outset of the model, and by controlling the limits of the layer thickness during the model evolution, we find improved stability and resolution convergence of the models.

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Improving subduction interface implementation in dynamic numerical models

10.5194/se-2019-11 ◽

2019 ◽

Author(s):

Dan Sandiford ◽

Louis Moresi

Keyword(s):

Subduction Zone ◽

Dynamic Models ◽

Numerical Models ◽

Methodological Issues ◽

Weak Layer ◽

Simple Strategy ◽

Subduction Zone Processes ◽

Improved Stability ◽

Physical Effects ◽

Interface Profile

Abstract. This study focuses on methodological issues related to dynamic subduction zone modelling. Numerical models often employ an entrained weak layer (WL approach) to facilitate decoupling between the subducting and overriding plates. In such a setup, the kinematics of the flow lead to width variations in the subduction interface. When a uniform-width interface is prescribed, a transient evolution of the interface thickness occurs, during which the volmetric flux along the interface profile establishes equilibrium. Width variations can exceed 4× during this stage, which may impact the effective strength of the interface, both through physical effects if the rheology is linear, and numerical effects if the fault becomes poorly resolved. This transient process induces strong sensitivity to model resolution, and may present a significant challenge to reproducibility. Developing more robust ways to model the subduction interface will enable fully dynamic models to address sensitive subduction-zone processes, such as metamorphism near the slab top. In this study we discuss a simple strategy aimed at improving the standard WL approach. By prescribing a variable thickness weak layer at the outset of the model, and by controlling the limits of the layer thickness during the model evolution, we find improved stability and resolution convergence of the models.

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

10.5194/egusphere-egu21-13160 ◽

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

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.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.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.

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Surface processes control on orogenic evolution: inferences from 3D coupled numerical models and observations from the India-Eurasia collision zone

10.5194/egusphere-egu21-8243 ◽

2021 ◽

Author(s):

Luuk van Agtmaal ◽

Attila Balazs ◽

Dave May ◽

Taras Gerya

Keyword(s):

Numerical Models ◽

Surface Processes ◽

Climatic Forcing ◽

Plate Convergence ◽

Thermal Fields ◽

Denudation Rates ◽

Collision Zone ◽

Sediment Transportation ◽

Modelling Techniques ◽

Evolution Modeling

The inherent links between tectonics, surface processes and climatic variations have long since been recognised as the main drivers for the evolution of orogens. Oceanic and continental subduction and collision processes lead to distinct topographic signals. Simultaneously, different climatic forcing factors and denudation rates substantially modify the style of deformation leading to different stress and thermal fields, strain localisation and even deep mantle evolution. An ideal area where the above-mentioned processes and their connections can be studied is the India-Eurasia collision zone.Understanding&#160;the complex interplay between tectonics, erosion, sediment transportation and deposition requires the coupled application of thermo-mechanical and surface processes modelling techniques. To this aim, we used a 3D coupled numerical modelling approach. The influence&#160;of different plate convergence, erosion and sedimentation rates has been tested by the thermo-mechanical code I3ELVIS (Gerya and Yuen, 2007) coupled to the diffusion-advection based (FDSPM) surface processes model.We show preliminary results to demonstrate&#160; that the diffusion-advection erosion implementation has significant effects on local and regional mass redistribution and topographic evolution within narrow, curved, high orogens such as the Himalayas and their syntaxes,&#160;where erosion is a dominant forcing factor. We also discuss possible implications from different erosion/sedimentation implementations such as DAC (Ueda et al., 2015; Goren et al., 2014) in combination with the reference thermo-mechanical model to analyse&#160;changes in orogenic development as a consequence of different erosional processes in more detail.References:Gerya, T. V., & Yuen, D. A. (2007). Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Physics of the Earth and Planetary Interiors, 163(1-4), 83-105. Ueda, K., Willett, S. D., Gerya, T., & Ruh, J. (2015). Geomorphological&#8211;thermo-mechanical modeling: Application to orogenic wedge dynamics. Tectonophysics, 659, 12-30. Goren, L., Willett, S. D., Herman, F., & Braun, J. (2014). Coupled numerical&#8211;analytical approach to landscape evolution modeling. Earth Surface Processes and Landforms, 39(4), 522-545.

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Resolution Dependence of Initiation and Upscale Growth of Deep Convection in Convection-Allowing Forecasts of the 31 May–1 June 2013 Supercell and MCS

Monthly Weather Review ◽

10.1175/mwr-d-15-0179.1 ◽

2015 ◽

Vol 143 (11) ◽

pp. 4331-4354 ◽

Cited By ~ 13

Author(s):

Russ S. Schumacher

Keyword(s):

Boundary Layer ◽

Numerical Models ◽

Deep Convection ◽

Squall Line ◽

Cold Pool ◽

Model Resolution ◽

Grid Spacing ◽

Boundary Layer Processes ◽

High Impact Weather ◽

Supercell Thunderstorm

Abstract On 31 May 2013, a supercell thunderstorm initiated in west-central Oklahoma and produced a deadly tornado. This convection then grew upscale, with a nearly stationary line developing early on 1 June that produced very heavy rainfall and caused deadly flash flooding in the Oklahoma City area. Real-time convection-allowing (Δx = 4 km) model forecasts used during the Mesoscale Predictability Experiment (MPEX) provided accurate guidance regarding the timing, location, and evolution of convection in this case. However, attempts to simulate this event at higher resolution degraded the forecast, with the primary supercell failing to initiate and the evolution of the overnight MCS not resembling the observed system. Experiments to test the dependence of forecasts of this event on model resolution show that with grid spacing smaller than 4 km, mixing along the dryline in northwest Texas was more vigorous, causing low-level dry air to move more quickly eastward into Oklahoma. This drying prevented the supercell from initiating near the triple point in the higher-resolution simulations. Then, the lack of supercellular convection and its associated cold pool altered the evolution of subsequent convection. Whereas in observations and the 4-km forecast, a nearly stationary MCS developed parallel to, but displaced from, the supercell’s cold pool, the higher-resolution simulations instead had a faster-moving squall line that produced less rainfall. Although the degradation of convective forecasts at higher resolution is probably unusual and appears sensitive to the choice of boundary layer parameterization, these findings demonstrate that how numerical models treat boundary layer processes at different grid spacings can, in some cases, have profound influences on predictions of high-impact weather.

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Coupled Sea Ice–Ocean-State Estimation in the Labrador Sea and Baffin Bay

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-065.1 ◽

2013 ◽

Vol 43 (5) ◽

pp. 884-904 ◽

Cited By ~ 34

Author(s):

Ian Fenty ◽

Patrick Heimbach

Keyword(s):

Sea Ice ◽

North Atlantic ◽

Numerical Models ◽

Labrador Sea ◽

In Situ Observation ◽

Quasi Equilibrium ◽

Ocean Variability ◽

The Relationship ◽

Ice Model

Abstract Sea ice variability in the Labrador Sea is of climatic interest because of its relationship to deep convection, mode-water formation, and the North Atlantic atmospheric circulation. Historically, quantifying the relationship between sea ice and ocean variability has been difficult because of in situ observation paucity and technical challenges associated with synthesizing observations with numerical models. Here the relationship between ice and ocean variability is explored by analyzing new estimates of the ocean–ice state in the northwest North Atlantic. The estimates are syntheses of in situ and satellite hydrographic and ice data with a regional ⅓° coupled ocean–sea ice model. The synthesis of sea ice data is achieved with an improved adjoint of a thermodynamic ice model. Model and data are made consistent, in a least squares sense, by iteratively adjusting control variables, including ocean initial and lateral boundary conditions and the atmospheric state, to minimize an uncertainty-weighted model–data misfit cost function. The utility of the state estimate is demonstrated in an analysis of energy and buoyancy budgets in the marginal ice zone (MIZ). In mid-March the system achieves a state of quasi-equilibrium during which net ice growth and melt approaches zero; newly formed ice diverges from coastal areas and converges via wind and ocean forcing in the MIZ. The convergence of ice mass in the MIZ is ablated primarily by turbulent ocean–ice enthalpy fluxes. The primary source of the enthalpy required for sustained MIZ ice ablation is the sensible heat reservoir of the subtropical-origin subsurface waters.

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Interactions between Shallow and Deep Convection under a Finite Departure from Convective Quasi Equilibrium

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0108.1 ◽

2012 ◽

Vol 69 (12) ◽

pp. 3463-3470 ◽

Cited By ~ 19

Author(s):

Jun-Ichi Yano ◽

Robert Plant

Keyword(s):

Large Scale ◽

Numerical Models ◽

Deep Convection ◽

Present Theory ◽

Convective System ◽

Quasi Equilibrium ◽

Shallow Convection ◽

Convective Clouds ◽

Flux Parameterization ◽

Stable Periodic

Abstract The present paper presents a simple theory for the transformation of nonprecipitating, shallow convection into precipitating, deep convective clouds. To make the pertinent point a much idealized system is considered, consisting only of shallow and deep convection without large-scale forcing. The transformation is described by an explicit coupling between these two types of convection. Shallow convection moistens and cools the atmosphere, whereas deep convection dries and warms the atmosphere, leading to destabilization and stabilization, respectively. Consequently, in their own stand-alone modes, shallow convection perpetually grows, whereas deep convection simply damps: the former never reaches equilibrium, and the latter is never spontaneously generated. Coupling the modes together is the only way to reconcile these undesirable separate tendencies, so that the convective system as a whole can remain in a stable periodic state under this idealized setting. Such coupling is a key missing element in current global atmospheric models. The energy cycle description used herein is fully consistent with the original formulation by Arakawa and Schubert, and is suitable for direct implementation into models using a mass flux parameterization. The coupling would alleviate current problems with the representation of these two types of convection in numerical models. The present theory also provides a pertinent framework for analyzing large-eddy simulations and cloud-resolving modeling.

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Numerical Models of Ice-Shelf Flow: Ideal/Real

Annals of Glaciology ◽

10.1017/s0260305500007035 ◽

1989 ◽

Vol 12 ◽

pp. 97-103 ◽

Cited By ~ 5

Author(s):

M.A. Lange ◽

D.R. MacAyeal

Keyword(s):

Numerical Models ◽

Field Measurements ◽

Ice Thickness ◽

Ice Shelf ◽

Model Calculations ◽

Ice Shelves ◽

Ice Stream ◽

Simple Geometry ◽

Thickness Variations ◽

Transient Variations

We present model calculations that describe the flow of ice shelves of different configurations. We consider “ideal” models with well-defined boundary conditions and simple geometry in order to explore the response of an ice shelf to transient variations in ice-stream input. Gradually increasing the complexity of these simple models allows a better understanding of ice-shelf behavior without the complications that would arise in considering natural ice shelves. We find that the dissipation of ice-thickness variations caused by ice-stream transience is strongly influenced by ice rheology. The presence of an ice rise significantly alters the velocity field of the adjacent ice, when changes in ice-stream input occur. With models of “real” ice shelves, we demonstrate the ability of numerical models to test successfully working hypotheses on ice-shelf thickness distributions. Ice velocities, obtained by diagnostic models of Filchner–Ronne Ice Shelf that use different ice-thickness distributions, are compared with measured ice velocities. This comparison demonstrates that the model employing regions of thin ice in the central part of the ice shelf yields velocities significantly different from the field data. We therefore conclude that zones of thin ice on Filchner–Ronne ice Shelf are unlikely. This conclusion has recently been confirmed by field measurements.

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Predictions of Residual Stresses and Deformations in Pipe Bends Produced Using Cold, Warm and Induction Bending Processes

Volume 2: Computer Technology and Bolted Joints ◽

10.1115/pvp2014-28774 ◽

2014 ◽

Cited By ~ 2

Author(s):

Y. Ding ◽

M. Yetisir ◽

S. Khajehpour

Keyword(s):

Residual Stress ◽

Residual Stresses ◽

Numerical Models ◽

Local Heating ◽

Safety Evaluation ◽

Stress Distributions ◽

Advantages And Disadvantages ◽

Cold Bending ◽

Bending Process ◽

Thickness Variations

Cold bending, warm bending (bending with local heating) and induction bending are three manufacturing processes widely used to produce pipe bends. The cold and warm bending processes have been used for the fabrication of carbon steel feeder bends for CANDU® reactors, and the induction bending process was considered for the fabrication of stainless steel feeder pipes for an advanced CANDU reactor. Bending processes result in plastic deformation, and inevitably, introduce residual stresses in the deformed pipes. Residual stresses in feeder bends are believed to be a very important contributing factor in feeder cracking. Different bending processes result in widely different residual stress patterns and magnitudes in pipe bends. Hence, it is important to understand the effect of bending processes and the process parameters used on the residual stress distribution in the bent pipes. Numerical models have been successfully developed to predict the residual stresses and the deformed shapes induced by cold, warm and induction bending processes. This paper provides a comprehensive review of the predicted residual stress distributions, ovality and wall-thickness variations of the cold, warm and induction bends. The predicted results were compared to earlier measurements of spare CANDU feeder bends and test bends. Advantages and disadvantages of the three bending processes are summarized. Numerical approaches for the modeling of residual stresses could be of benefit to engineering estimates of residual stresses in feeder pipes for safety evaluation of nuclear reactors.

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The Dynamics of Mixed Layer Deepening during Open-Ocean Convection

Journal of Physical Oceanography ◽

10.1175/jpo-d-19-0264.1 ◽

2020 ◽

Vol 50 (6) ◽

pp. 1625-1641

Author(s):

Taimoor Sohail ◽

Bishakhdatta Gayen ◽

Andrew McC. Hogg

Keyword(s):

Mixed Layer ◽

Large Scale ◽

Numerical Models ◽

Mixed Layer Depth ◽

Baroclinic Instability ◽

Open Ocean ◽

Scale Model ◽

Quasi Equilibrium ◽

Layer Depth ◽

Ocean Convection

AbstractOpen-ocean convection is a common phenomenon that regulates mixed layer depth and ocean ventilation in the high-latitude oceans. However, many climate model simulations overestimate mixed layer depth during open-ocean convection, resulting in excessive formation of dense water in some regions. The physical processes controlling transient mixed layer depth during open-ocean convection are examined using two different numerical models: a high-resolution, turbulence-resolving nonhydrostatic model and a large-scale hydrostatic ocean model. An isolated destabilizing buoyancy flux is imposed at the surface of both models and a quasi-equilibrium flow is allowed to develop. Mixed layer depth in the turbulence-resolving and large-scale models closely aligns with existing scaling theories. However, the large-scale model has an anomalously deep mixed layer prior to quasi-equilibrium. This transient mixed layer depth bias is a consequence of the lack of resolved turbulent convection in the model, which delays the onset of baroclinic instability. These findings suggest that in order to reduce mixed layer biases in ocean simulations, parameterizations of the connection between baroclinic instability and convection need to be addressed.

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

10.5194/egusphere-egu21-2441 ◽

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

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 km3/yr and ~88 km3/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,&#160;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 d&#233;collement 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 &#8220;westward&#8221;-directed slabs, whereas H-convergent are compatible with those that have &#8220;eastward-to-northeastward&#8221;-directed slabs. On the basis of this geographical polarity of subducting slabs, the obtained lithospheric volume estimation gives ~214 km3/yr and ~88 km3/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 km3/yr of mantle material from the west to the east, providing a constrain for a global asymmetric mantle convection.

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