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Abstract The determination of the temperature in and above the slab in subduction zones, using models where the top of the slab is precisely known, is important to test hypotheses regarding the causes of arc volcanism and intermediate-depth seismicity. While 2D and 3D models can predict the thermal structure with high precision for fixed slab geometries, a number of regions are characterized by relatively large geometrical changes over time. Examples include the flat slab segments in South America that evolved from more steeply dipping geometries to the present day flat slab geometry. We devise, implement, and test a numerical approach to model the thermal evolution of a subduction zone with prescribed changes in slab geometry over time. Our numerical model approximates the subduction zone geometry by employing time dependent deformation of a Bézier spline that is used as the slab interface in a finite element discretization of the Stokes and heat equations. We implement the numerical model using the FEniCS open source finite element suite and describe the means by which we compute approximations of the subduction zone velocity, temperature, and pressure fields. We compute and compare the 3D time evolving numerical model with its 2D analogy at cross-sections for slabs that evolve to the present-day structure of a flat segment of the subducting Nazca plate.
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Linking Visco‐Elasto‐Plastic Modeling of Recent Slab Deformation to Present‐Day Deep Earthquakes
Abstract Deep earthquakes require the cold temperatures found in sinking lithosphere to store elastic strain. It has also been proposed that sufficiently high rates of deformation are also required, regardless of the failure mechanism. However, this strain‐rate hypothesis is based on generic time‐dependent and visco‐plastic subduction models, positing a challenge for direct comparisons to present‐day earthquake observations. Here, we present a new numerical modeling approach incorporating location‐specific visco‐elasto‐plastic models to facilitate direct comparison with deep earthquake observations. We present a Proof‐of‐Concept Model using a 2D synthetic slab to demonstrate that this novel approach can reproduce stress and strain‐rate patterns and the stress orientations from a fully time‐dependent model. Applying this method to a 2D profile through the Tonga‐Kermadec subduction zone we find that variations in strain‐rate correlate with seismicity rate and regions of stress in the slab exceeding 500 MPa. Elasticity in the slab leads to formation of a clearly defined neutral plane extending into the transition zone and creating a narrow region of down‐dip compression along the top portion of the slab which broadens across the full width of the slab only within the deep transition zone. In addition, assuming that the strain‐rate hypothesis is correct, we show that peaks in strain‐rate, which are associated with bends in the slab, could be used to constrain the slab shape beyond the envelope of seismicity.
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- Award ID(s):
- 2121800
- PAR ID:
- 10577109
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 130
- Issue:
- 3
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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