Unravelling tectonic coupling and loading along the Sunda margin through 3-D regional numerical modelling

[gthyagi]

-> submitter ORCID (or name)

0000-0001-9394-4104

-> slug

gollapalli-2022-sunda-subduction

-> license

CC-BY-4.0

-> alternative license URL

No response

-> model category

model published in study, forward model

-> model status

completed

-> associated publication DOI

https://doi.org/10.26180/21664034.v1

-> model creators

0000-0001-9394-4104

-> title

Subduction dynamics and plate coupling along seismically active margin: the role of slab steps

-> description

The negative buoyancy of the slab drives subducting plate and trench motions, influencing tectonic stresses at convergent margins. Variations in slab depth along the trench affect plate coupling and seismicity. We investigated these effects using 3-D subduction models, focusing on slab depth variations and their impact on force balance. Results show convergence velocity is primarily controlled by slab mass and subducting plate rheology, while trench movement is sensitive to slab depth heterogeneity. The highest stress occurs around slab steps, aligning with deformation patterns observed along the Sunda margin. This study highlights the crucial role of trench-parallel forces in plate dynamics.

-> abstract

The negative buoyancy of the slab primarily controls the subducting plate and trench motions, and tectonic stresses around the convergent margins. Lateral variations in negative buoyancy associated with varying slab depth along strike must affect plate and margin motions, and, most importantly, have an impact on the stress acting across the margin, thereby setting the context for plate coupling, tectonics and present-day seismicity. Here, we investigated these interactions in 3-D subduction numerical models, focusing on along-trench variations in the subduction depth and the resulting perturbations to the force balance. While we focus on the steps in the slab depth, we additionally test the role of subducting plate, i.e., cohesion and viscosity, and upper plate properties, i.e., thickness, viscosity, and cohesion. The results show that the magnitude of convergence velocity only depends on the integrated slab mass and rheology of the subducting plate when the upper plate is thin. Instead, the trench retreat/advance is sensitive to the heterogeneity in the slab depth, and a complex pattern arises atop the slab step, with a characteristic length of ~500 km from the slab depth perturbation. The remaining parameters of the subducting and upper plate mainly affect the magnitude of the trench velocities with minor influence on the pattern. The highest deformation/stress in the upper plate is observed around the slab step due to the rigidity of the plate, causing mutual perturbation between the deep and shallow slab portions, and the lateral flow around the step. These results are compared with the observations along the Sunda margin, where similar slab depth variations are found. The upper plate deformation in the model shows remarkable compatibility with the observed distributions of compression and extension of the Andaman- Sumatra-Java segments. Our study indicates that trench-parallel forces, arising from the natural variations of slab depth, exert a first-order control on the plate coupling and deformation along convergent margins and should not be neglected.

-> scientific keywords

No response

-> funder

No response

-> model embargo?

No response

-> include model code ?

• yes

-> model code/inputs DOI

https://doi.org/10.5281/zenodo.7022845

-> model code/inputs notes

Underworld2 input files of Sunda Subduction Zone (3D cartesian models).

-> include model output data?

• yes

-> data creators

No response

-> model output data DOI

No response

-> model output data notes

Output data mainly contains *.h5 and *.xdmf files.

-> model output data size

3 TB

-> software framework DOI/URI

https://doi.org/10.5281/zenodo.3975252

-> software framework source repository

No response

-> name of primary software framework (e.g. Underworld, ASPECT, Badlands, OpenFOAM)

No response

-> software framework authors

No response

-> software & algorithm keywords

No response

-> computer URI/DOI

https://dx.doi.org/10.25914/608bfd1838db2

-> add landing page image and caption

Mantle flow and upper plate deformation due to slab step

-> add an animation (if relevant)

Mantle flow and upper plate deformation due to slab step

-> add a graphic abstract figure (if relevant)

Sketch of the tectonic forces acting at the Sunda margin and interface stress along Andaman (DD’), Sumatra (FF’), and Java (MM’). At the Sumatra margin, an additional transferred force ($F^*_{SP}$) from Java is acting that contributes to crustal thickening/compression in the upper plate. The blue stars represent the interplate earthquakes, and black dots are intraplate seismicity. The sketch neglects the curvature of the trench and the obliquity of convergence.

-> add a model setup figure (if relevant)

Numerical model setup. The parameter d denotes the depth of the long slab (i.e., 660 km, green plane), and Δ𝑑 represents step length (i.e., the difference between the long and short slab). The long and short slabs extend from 0-2000 and 2000-4000 km in the Y-direction. The trench is located at X = 2000 km.

-> add a description of your model setup

The model setup consists of the subducting plate with attached slab and upper plate inserted in the 660 km upper mantle lying over 340 km lower mantle. The model extends 4000 km in each x, y, and 1000 km in the z-axis with a numerical resolution of 512×512×128, respectively. This resolution results in an element size of 7.8 km in all three directions. Each element is populated with 20 Lagrangian particles to store material properties. All boundaries in the model are under free slip conditions. All models include a 100 km thick subducting plate and slab. The rheology in the top 30 km (crust) is viscoplastic, and the rest (70 km lithospheric mantle) is viscous. Oceanic lithosphere has a density contrast of 50 $kg/m^3$ with respect to the underlying sublithospheric mantle. The entire slab has a uniform initial dip angle of 45°. The upper plate consists of crust 30 km thick, and its lithospheric mantle thickness is varied between 20 km, 40 km, and 60 km. The trailing end of the subducting plate is free and upper plate end is fixed. The density contrast between the upper plate and mantle is set to zero. This avoids lithostatic pressure gradients, and the stress distribution in the upper plate is only influenced by the dynamics driven by lateral slab buoyancy variations. Therefore, the stress distribution in the upper plate can be used as a proxy for tectonic coupling at the interface.

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Section 1: Summary of your model

Model Submitter:

Thyagarajulu Gollapalli (0000-0001-9394-4104)

Model Creator(s):

• Thyagarajulu Gollapalli (0000-0001-9394-4104)

Model slug:

gollapalli-2022-sunda-subduction

(this will be the name of the model repository when created)

Model name:

Subduction dynamics and plate coupling along seismically active margin: the role of slab steps

License:

Creative Commons Attribution 4.0 International

Model Category:

• model published in study
• forward model

Model Status:

• completed

Short description:

The negative buoyancy of the slab drives subducting plate and trench motions, influencing tectonic stresses at convergent margins. Variations in slab depth along the trench affect plate coupling and seismicity. We investigated these effects using 3-D subduction models, focusing on slab depth variations and their impact on force balance. Results show convergence velocity is primarily controlled by slab mass and subducting plate rheology, while trench movement is sensitive to slab depth heterogeneity. The highest stress occurs around slab steps, aligning with deformation patterns observed along the Sunda margin. This study highlights the crucial role of trench-parallel forces in plate dynamics.

Abstract:

The negative buoyancy of the slab primarily controls the subducting plate and trench motions, and tectonic stresses around the convergent margins. Lateral variations in negative buoyancy associated with varying slab depth along strike must affect plate and margin motions, and, most importantly, have an impact on the stress acting across the margin, thereby setting the context for plate coupling, tectonics and present-day seismicity. Here, we investigated these interactions in 3-D subduction numerical models, focusing on along-trench variations in the subduction depth and the resulting perturbations to the force balance. While we focus on the steps in the slab depth, we additionally test the role of subducting plate, i.e., cohesion and viscosity, and upper plate properties, i.e., thickness, viscosity, and cohesion. The results show that the magnitude of convergence velocity only depends on the integrated slab mass and rheology of the subducting plate when the upper plate is thin. Instead, the trench retreat/advance is sensitive to the heterogeneity in the slab depth, and a complex pattern arises atop the slab step, with a characteristic length of ~500 km from the slab depth perturbation. The remaining parameters of the subducting and upper plate mainly affect the magnitude of the trench velocities with minor influence on the pattern. The highest deformation/stress in the upper plate is observed around the slab step due to the rigidity of the plate, causing mutual perturbation between the deep and shallow slab portions, and the lateral flow around the step. These results are compared with the observations along the Sunda margin, where similar slab depth variations are found. The upper plate deformation in the model shows remarkable compatibility with the observed distributions of compression and extension of the Andaman- Sumatra-Java segments. Our study indicates that trench-parallel forces, arising from the natural variations of slab depth, exert a first-order control on the plate coupling and deformation along convergent margins and should not be neglected.

Funder(s):

• No response

Section 2: your model code, output data

No embargo on model contents requested

Include model code:

True

Model code existing URL/DOI:

https://doi.org/10.5281/zenodo.7022845

Model code notes:

Underworld2 input files of Sunda Subduction Zone (3D cartesian models).

Include model output data:

True

Model output data notes:

Output data mainly contains *.h5 and *.xdmf files.

Section 3: software framework and compute details

Software Framework DOI/URL:

Found software: Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud

Name of primary software framework:

Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud

Section 4: web material (for mate.science)

Landing page image:

Filename: vel_sr_inv_landing_page.png
Caption:
Mantle flow and upper plate deformation due to slab step

Animation:

Filename: side_view_snapshot.png
Caption:
Mantle flow and upper plate deformation due to slab step

Graphic abstract:

Filename: sketch.png
Caption:
Sketch of the tectonic forces acting at the Sunda margin and interface stress along Andaman (DD’), Sumatra (FF’), and Java (MM’). At the Sumatra margin, an additional transferred force ($F^*_{SP}$) from Java is acting that contributes to crustal thickening/compression in the upper plate. The blue stars represent the interplate earthquakes, and black dots are intraplate seismicity. The sketch neglects the curvature of the trench and the obliquity of convergence.

Model setup figure:

Filename: model_matvar_edit_model_setup.png
Caption:
Numerical model setup. The parameter d denotes the depth of the long slab (i.e., 660 km, green plane), and Δ𝑑 represents step length (i.e., the difference between the long and short slab). The long and short slabs extend from 0-2000 and 2000-4000 km in the Y-direction. The trench is located at X = 2000 km.
Description: The model setup consists of the subducting plate with attached slab and upper plate inserted in the 660 km upper mantle lying over 340 km lower mantle. The model extends 4000 km in each x, y, and 1000 km in the z-axis with a numerical resolution of 512×512×128, respectively. This resolution results in an element size of 7.8 km in all three directions. Each element is populated with 20 Lagrangian particles to store material properties. All boundaries in the model are under free slip conditions. All models include a 100 km thick subducting plate and slab. The rheology in the top 30 km (crust) is viscoplastic, and the rest (70 km lithospheric mantle) is viscous. Oceanic lithosphere has a density contrast of 50 $kg/m^3$ with respect to the underlying sublithospheric mantle. The entire slab has a uniform initial dip angle of 45°. The upper plate consists of crust 30 km thick, and its lithospheric mantle thickness is varied between 20 km, 40 km, and 60 km. The trailing end of the subducting plate is free and upper plate end is fixed. The density contrast between the upper plate and mantle is set to zero. This avoids lithostatic pressure gradients, and the stress distribution in the upper plate is only influenced by the dynamics driven by lateral slab buoyancy variations. Therefore, the stress distribution in the upper plate can be used as a proxy for tectonic coupling at the interface.

Errors and Warnings

Associated Publication
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Submitter
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Model creators
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Model Repository Slug
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Model output DOI
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Model repository created at https://github.com/ModelAtlasofTheEarth/gollapalli-2022-sunda-subduction